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Mac OS X 10.6 Snow Leopard: the Ars Technica review | killexams.com real questions and Pass4sure dumps

Mac OS X 10.6 Snow Leopard: the Ars Technica review reader comments 454 with 269 posters participating, including narrative author Share this story
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  • Mac OS X 10.4 Tiger: 150+  novel featuresMac OS X 10.4 Tiger: 150+ novel features

    In June of 2004, during the WWDC keynote address, Steve Jobs revealed Mac OS X 10.4 Tiger to developers and the public for the first time. When the finished product arrived in April of 2005, Tiger was the biggest, most important, most feature-packed release in the history of Mac OS X by a wide margin. Apple's marketing drive reflected this, touting "over 150 novel features."

    All those novel features took time. Since its introduction in 2001, there had been at least one major release of Mac OS X each year. Tiger took over a year and a half to arrive. At the time, it definitely seemed worth the wait. Tiger was a hit with users and developers. Apple took the lesson to heart and quickly set expectations for the next major release of Mac OS X, Leopard. Through various channels, Apple communicated its goal to run from a 12-month to an 18-month release cycle for Mac OS X. Leopard was officially scheduled for "spring 2007."

    As the date approached, Apple's marketing machine trod a predictable path.

    Steve Jobs at WWDC 2007, touting 300  novel features in Mac OS X 10.5 LeopardSteve Jobs at WWDC 2007, touting 300 novel features in Mac OS X 10.5 Leopard

    Apple even went so far as to list complete 300 novel features on its website. As it turns out, "spring" was a bit optimistic. Leopard actually shipped at the terminate of October 2007, nearly two and a half years after Tiger. Did Leopard really possess twice as many novel features as Tiger? That's debatable. What's unavoidable is that Leopard included a solid crop of novel features and technologies, many of which they now Take for granted. (For example, possess you had a discussion with a potential Mac user since the release of Leopard without mentioning Time Machine? I certainly haven't.)

    Mac OS X appeared to exist maturing. The progression was clear: longer release cycles, more features. What would Mac OS X 10.6 exist like? Would it arrive three and a half years after Leopard? Would it and involve 500 novel features? A thousand?

    At WWDC 2009, Bertrand Serlet announced a run that he described as "unprecedented" in the PC industry.

    Mac OS X 10.6 - Read Bertrand's lips: No  novel Features!Mac OS X 10.6 - Read Bertrand's lips: No novel Features!

    That's right, the next major release of Mac OS X would possess no novel features. The product cognomen reflected this: "Snow Leopard." Mac OS X 10.6 would merely exist a variant of Leopard. Better, faster, more refined, more... uh... snowy.

    This was a risky strategy for Apple. After the rapid-fire updates of 10.1, 10.2, and 10.3 followed by the riot of novel features and APIs in 10.4 and 10.5, could Apple really acquire away with calling a "time out?" I imagine Bertrand was really sweating this announcement up on the stage at WWDC in front of a live audience of Mac developers. Their reaction? impulsive applause. There were even a few hoots and whistles.

    Many of these selfsame developers applauded the "150+ novel features" in Tiger and the "300 novel features" in Leopard at past WWDCs. Now they were applauding zero novel features for Snow Leopard? What explains this?

    It probably helps to know that the "0 novel Features" skid came at the terminate of an hour-long presentation detailing the major novel APIs and technologies in Snow Leopard. It was also quickly followed by a back-pedaling ("well, there is one novel feature...") skid describing the addition of Microsoft Exchange support. In isolation, "no novel features" may seem to imply stagnation. In context, however, it served as a developer-friendly affirmation.

    The overall message from Apple to developers was something like this: "We're adding a ton of novel things to Mac OS X that will abet you write better applications and accomplish your existing code accelerate faster, and we're going to accomplish positive that complete this novel stuff is rock-solid and as bug-free as possible. We're not going to overextend ourselves adding a raft of novel customer-facing, marketing-friendly features. Instead, we're going to concentrate 100% on the things that strike you, the developers."

    But if Snow Leopard is a value epistle to developers, is it a Dear John epistle to users? You know, those people that the marketing department might so crudely advert to as "customers." What's in it for them? Believe it or not, the sales pitch to users is actually quite similar. As exhausting as it has been for developers to retain up with Apple's seemingly never-ending stream of novel APIs, it can exist just as taxing for customers to stay on top of Mac OS X's features. Exposé, a novel Finder, Spotlight, a novel Dock, Time Machine, a novel Finder again, a novel iLife and iWork almost every year, and on and on. And as much as developers loathe bugs in Apple's APIs, users who experience those bugs as application crashes possess just as much understanding to exist annoyed.

    Enter Snow Leopard: the release where they complete acquire a fracture from the new-features/new-bugs treadmill of Mac OS X development. That's the pitch.

    Uncomfortable realities

    But wait a second, didn't I just mention an "hour-long presentation" about Snow Leopard featuring "major novel APIs and technologies?" When speaking to developers, Apple's message of "no novel features" is another passage of epigram "no novel bugs." Snow Leopard is hypothetical to fix aged bugs without introducing novel ones. But nothing says "new bugs, coming perquisite up" quite like major novel APIs. So which is it?

    Similarly, for users, "no novel features" connotes stability and reliability. But if Snow Leopard includes enough changes to the core OS to fill an hour-long overview session at WWDC more than a year before its release, can Apple really accomplish top-notch on this promise? Or will users terminate up with complete the disadvantages of a feature-packed release like Tiger or Leopard—the inevitable 10.x.0 bugs, the unfamiliar, untried novel functionality—but without any of the actual novel features?

    Yes, it's enough to accomplish one quite cynical about Apple's real motivations. To fling some more fuel on the fire, possess a peek at the Mac OS X release timeline below. Next to each release, I've included a list of its most significant features.

    Mac OS X release timelineMac OS X release timeline

    That curve is taking on a decidedly droopy shape, as if it's being weighed down by the ever-increasing number of novel features. (The releases are distributed uniformly on the Y axis.) Maybe you reflect it's reasonable for the time between releases to stretch out as each one brings a heavier load of goodies than the last, but retain in intellect the logical consequence of such a curve over the longhorn haul.

    And yeah, there's a miniature upwards kick at the terminate for 10.6, but remember, this is hypothetical to exist the "no novel features" release. Version 10.1 had a similar no-frills focus but took a heck of a lot less time to arrive.

    Looking at this graph, it's difficult not to prodigy if there's something siphoning resources from the Mac OS X development effort. Maybe, say, some project that's in the first two or three major releases of its life, soundless in that steep, early section of its own timeline graph. Yes, I'm talking about the iPhone, specifically iPhone OS. The iPhone traffic has exploded onto Apple's equipoise sheets like no other product before, even the iPod. It's also accruing developers at an alarming rate.

    It's not a stretch to imagine that many of the artists and developers who piled on the user-visible features in Mac OS X 10.4 and 10.5 possess been reassigned to iPhone OS (temporarily or otherwise). After all, Mac OS X and iPhone OS participate the selfsame core operating system, the selfsame language for GUI development, and many of the selfsame APIs. Some workforce migration seems inevitable.

    And let's not forget the "Mac OS X" technologies that they later scholarly were developed for the iPhone and just happened to exist announced for the Mac first (because the iPhone was soundless a secret), like Core Animation and code signing. Such collusion theories certainly aren't helped by WWDC keynote snubs and other indignities suffered by Mac OS X and the Mac in common since the iPhone arrived on the scene. And so, on top of everything else, Snow Leopard is tasked with restoring some luster to Mac OS X.

    Got complete that? A nearly two-year development cycle, but no novel features. Major novel frameworks for developers, but few novel bugs. Significant changes to the core OS, but more reliability. And a franchise rejuvenation with few user-visible changes.

    It's enough to turn a leopard white.

    The price of entry

    Snow Leopard's opening overture to consumers is its price: $29 for those upgrading from Leopard. The debut release of Mac OS X 10.0 and the last four major releases possess complete been $129, with no special pricing for upgrades. After eight years of this kindly of fiscal disciplining, Leopard users may well exist tempted to quit reading perquisite now and just proceed pick up a copy. Snow Leopard's upgrade price is well under the impulse purchase threshold for many people. Twenty-nine dollars plus some minimal flush of faith in Apple's skill to better the OS with each release, and boom, instant purchase.

    Still here? Good, because there's something else you need to know about Snow Leopard. It's an overture of a different sort, less of a come-on and more of a spur. Snow Leopard will only accelerate on Macs with Intel CPUs. Sorry (again), PowerPC fans, but this is the terminate of the line for you. The transition to Intel was announced over four years ago, and the last novel PowerPC Mac was released in October 2005. It's time.

    But if Snow Leopard is meant to prod the PowerPC holdouts into the Intel age, its "no novel features" stance (and the accompanying lack of added visual flair) is working against it. For those running Leopard on a PowerPC-based Mac, there's precious miniature in Snow Leopard to abet thrust them over the (likely) four-digit price wall of a novel Mac. For PowerPC Mac owners, the threshold for a novel Mac purchase remains mostly unchanged. When their aged Mac breaks or seems too slow, they'll proceed out and buy a novel one, and it'll approach with Snow Leopard pre-installed.

    If Snow Leopard does terminate up motivating novel Mac purchases by PowerPC owners, it will probably exist the result of resignation rather than inspiration. An Intel-only Snow Leopard is most significant for what it isn't: a further extension of PowerPC life back on the Mac platform.

    The final gripping group is owners of Intel-based Macs that are soundless running Mac OS X 10.4 Tiger. Apple shipped Intel Macs with Tiger installed for a miniature over one year and nine months. Owners of these machines who never upgraded to Leopard are not eligible for the $29 upgrade to Snow Leopard. They're also apparently not eligible to purchase Snow Leopard for the traditional $129 price. Here's what Apple has to philosophize about Snow Leopard's pricing (emphasis added).

    Mac OS X version 10.6 Snow Leopard will exist available as an upgrade to Mac OS X version 10.5 Leopard in September 2009 [...] The Snow Leopard lone user license will exist available for a suggested retail price of $29 (US) and the Snow Leopard Family Pack, a lone household, five-user license, will exist available for a suggested price of $49 (US). For Tiger® users with an Intel-based Mac, the Mac Box Set includes Mac OS X Snow Leopard, iLife® '09 and iWork® '09 and will exist available for a suggested price of $169 (US) and a Family Pack is available for a suggested price of $229 (US).

    Ignoring the family packs for a moment, this means that Snow Leopard will either exist free with your novel Mac, $29 if you're already running Leopard, or $169 if you possess an Intel Mac running Tiger. People upgrading from Tiger will acquire the latest version of iLife and iWork in the covenant (if that's the preempt term), whether they want them or not. It positive seems like there's an obvious position in this lineup for a $129 offering of Snow Leopard on its own. Then again, perhaps it complete comes down to how, exactly, Apple enforces the $29 Snow Leopard upgrade policy.

    (As an aside to non-Mac users, note that the non-server version of Mac OS X has no per-user serial number and no activation scheme of any kind, and never has. "Registration" with Apple during the Mac OS X install process is entirely optional and is only used to collect demographic information. Failing to register (or entering entirely bogus registration information) has no result on your skill to accelerate the OS. This is considered a genuine advantage of Mac OS X, but it also means that Apple has no accountable record of who, exactly, is a "legitimate" owner of Leopard.)

    One possibility was that the $29 Snow Leopard upgrade DVD would only install on top of an existing installation of Leopard. Apple has done this sort of thing before, and it bypasses any proof-of-purchase annoyances. It would, however, interlard a novel problem. In the event of a difficult drive failure or simple decision to reinstall from scratch, owners of the $29 Snow Leopard upgrade would exist forced to first install Leopard and then install Snow Leopard on top of it, perhaps more than doubling the installation time—and quintupling the annoyance.

    Given Apple's history in this area, no one should possess been surprised to find out that Apple chose the much simpler option: the $29 "upgrade" DVD of Snow Leopard will, in fact, install on any supported Mac, whether or not it has Leopard installed. It will even install onto an entirely empty difficult drive.

    To exist clear, installing the $29 upgrade to Snow Leopard on a system not already running a properly licensed copy of Leopard is a violation of the end-user license agreement that comes with the product. But Apple's decision is a refreshing change: rewarding honest people with a hassle-free product rather than trying to castigate dishonest people by treating everyone like a criminal. This "honor system" upgrade enforcement policy partially explains the titanic jump to $169 for the Mac Box Set, which ends up re-framed as an honest person's passage to acquire iLife and iWork at their accustomed prices, plus Snow Leopard for $11 more.

    And yes, speaking of installing, let's finally acquire on with it.


    Apple claims that Snow Leopard's installation process is "up to 45% faster." Installation times vary wildly depending on the speed, contents, and fragmentation of the target disk, the accelerate of the optical drive, and so on. Installation also only happens once, and it's not really an gripping process unless something goes terribly wrong. Still, if Apple's going to accomplish such a claim, it's worth checking out.

    To purge as many variables as possible, I installed both Leopard and Snow Leopard from one difficult disk onto another (empty) one. It should exist celebrated that this change negates some of Snow Leopard's most necessary installation optimizations, which are focused on reducing random data access from the optical disc.

    Even with this disadvantage, the Snow Leopard installation took about 20% less time than the Leopard installation. That's well short of Apple's "up to 45%" claim, but see above (and don't forget the "up to" weasel words). Both versions installed in less than 30 minutes.

    What is striking about Snow Leopard's installation is how quickly the initial Spotlight indexing process completed. Here, Snow Leopard was 74% faster in my testing. Again, the times are tiny (5:49 vs. 3:20) and again, novel installations on empty disks are not the norm. But the shorter wait for Spotlight indexing is worth noting because it's the first indication most users will acquire that Snow Leopard means traffic when it comes to performance.

    Another notable thing about installation is what's not installed by default: Rosetta, the facility that allows PowerPC binaries to accelerate on Intel Macs. Okay Apple, they acquire it. PowerPC is a stiff, bereft of life. It rests in peace. It's rung down the curtain and joined the choir invisible. As far as Apple is concerned, PowerPC is an ex-ISA.

    But not installing Rosetta by default? That seems a miniature harsh, even foolhardy. What's going to betide when complete those users upgrade to Snow Leopard and then double-click what they've probably long since forgotten is a PowerPC application? Perhaps surprisingly, this is what happens:

    Rosetta: auto-installed for your convenienceRosetta: auto-installed for your convenience

    That's what I saw when I tried to launch Disk Inventory X on Snow Leopard, an application that, yes, I had long since forgotten was PowerPC-only. After I clicked the "Install" button, I actually expected to exist prompted to insert the installer DVD. Instead, Snow Leopard reached out over the network, pulled down Rosetta from an Apple server, and installed it.

    Rosetta auto-install

    No reboot was required, and Disk Inventory X launched successfully after the Rosetta installation completed. Mac OS X has not historically made much expend of the install-on-demand approach to system software components, but the facility used to install Rosetta appears quite robust. Upon clicking "Install," an XML property list containing a vast catalog of available Mac OS X packages was downloaded. Snow Leopard uses the selfsame facility to download and install printer drivers on demand, saving another trip to the installer DVD. I hope this technique gains even wider expend in the future.

    Installation footprint

    Rosetta aside, Snow Leopard simply puts fewer bits on your disk. Apple claims it "takes up less than half the disk space of the previous version," and that's no lie. A clean, default install (including fully-generated Spotlight indexes) is 16.8 GB for Leopard and 5.9 GB for Snow Leopard. (Incidentally, these numbers are both powers-of-two measurements; see sidebar.)

    A gigabyte by any other name

    Snow Leopard has another trick up its sleeve when it comes to disk usage. The Snow Leopard Finder considers 1 GB to exist equal to 109 (1,000,000,000) bytes, whereas the Leopard Finder—and, it should exist noted, every version of the Finder before it—equates 1 GB to 230 (1,073,741,824) bytes. This has the result of making your difficult disk suddenly materialize larger after installing Snow Leopard. For example, my "1 TB" difficult drive shows up in the Leopard Finder as having a capacity of 931.19 GB. In Snow Leopard, it's 999.86 GB. As you might possess guessed, difficult disk manufacturers expend the powers-of-ten system. It's complete quite a mess, really. Though I approach down pretty firmly on the powers-of-two side of the fence, I can't blame Apple too much for wanting to match up nicely with the long-established (but soundless dumb, intellect you) difficult disk vendors' capacity measurement standard.

    Snow Leopard has several weight loss secrets. The first is obvious: no PowerPC back means no PowerPC code in executables. Recall the maximum feasible binary payload in a Leopard executable: 32-bit PowerPC, 64-bit PowerPC, x86, and x86_64. Now cross half of those architectures off the list. Granted, very few applications in Leopard included 64-bit code of any kind, but it's a 50% reduction in size for executables no matter how you slice it.

    Of course, not complete the files in the operating system are executables. There are data files, images, audio files, even a miniature video. But most of those non-executable files possess one thing in common: they're usually stored in compressed file formats. Images are PNGs or JPEGs, audio is AAC, video is MPEG-4, even preference files and other property lists now default to a compact binary format rather than XML.

    In Snow Leopard, other kinds of files climb on board the compression bandwagon. To give just one example, ninety-seven percent of the executable files in Snow Leopard are compressed. How compressed? Let's look:

    % cd Applications/Mail.app/Contents/MacOS % ls -l Mail -rwxr-xr-x@ 1 root wheel 0 Jun 18 19:35 Mail

    Boy, that's, uh, pretty small, huh? Is this really an executable or what? Let's check their assumptions.

    % file Applications/Mail.app/Contents/MacOS/Mail Applications/Mail.app/Contents/MacOS/Mail: empty

    Yikes! What's going on here? Well, what I didn't divulge you is that the commands shown above were accelerate from a Leopard system looking at a Snow Leopard disk. In fact, complete compressed Snow Leopard files materialize to contain zero bytes when viewed from a pre-Snow Leopard version of Mac OS X. (They peek and act perfectly household when booted into Snow Leopard, of course.)

    So, where's the data? The miniature "@" at the terminate of the permissions string in the ls output above (a feature introduced in Leopard) provides a clue. Though the Mail executable has a zero file size, it does possess some extended attributes:

    % xattr -l Applications/Mail.app/Contents/MacOS/Mail com.apple.ResourceFork: 0000 00 00 01 00 00 2C F5 F2 00 2C F4 F2 00 00 00 32 .....,...,.....2 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ (184,159 lines snipped) 2CF610 63 6D 70 66 00 00 00 0A 00 01 FF FF 00 00 00 00 cmpf............ 2CF620 00 00 00 00 .... com.apple.decmpfs: 0000 66 70 6D 63 04 00 00 00 A0 82 72 00 00 00 00 00 fpmc......r.....

    Ah, there's complete the data. But wait, it's in the resource fork? Weren't those deprecated about eight years ago? Indeed they were. What you're witnessing here is yet another addition to Apple's favorite file system hobbyhorse, HFS+.

    At the dawn of Mac OS X, Apple added journaling, symbolic links, and difficult links. In Tiger, extended attributes and access control lists were incorporated. In Leopard, HFS+ gained back for difficult links to directories. In Snow Leopard, HFS+ learns another novel trick: per-file compression.

    The presence of the com.apple.decmpfs ascribe is the first hint that this file is compressed. This ascribe is actually hidden from the xattr command when booted into Snow Leopard. But from a Leopard system, which has no scholarship of its special significance, it shows up as unostentatious as day.

    Even more information is revealed with the abet of Mac OS X Internals guru Amit Singh's hfsdebug program, which has quietly been updated for Snow Leopard.

    % hfsdebug /Applications/Mail.app/Contents/MacOS/Mail ... compression magic = cmpf compression sort = 4 (resource fork has compressed data) uncompressed size = 7500336 bytes

    And positive enough, as they saw, the resource fork does indeed contain the compressed data. Still, why the resource fork? It's complete section of Apple's usual, clever backward-compatibility gymnastics. A recent sample is the passage that difficult links to directories define up—and function—as aliases when viewed from a pre-Leopard version of Mac OS X.

    In the case of a HFS+ compression, Apple was (understandably) unable to accomplish pre-Snow Leopard systems read and interpret the compressed data, which is stored in ways that did not exist at the time those earlier operating systems were written. But rather than letting applications (and users) running on pre-10.6 systems choke on—or worse, debase through modification—the unexpectedly compressed file contents, Apple has chosen to cloak the compressed data instead.

    And where can the complete contents of a potentially large file exist hidden in such a passage that pre-Snow Leopard systems can soundless copy that file without the loss of data? Why, in the resource fork, of course. The Finder has always correctly preserved Mac-specific metadata and both the resource and data forks when affecting or duplicating files. In Leopard, even the lowly cp and rsync commands will achieve the same. So while it may exist a miniature bit spooky to see complete those "empty" 0 KB files when looking at a Snow Leopard disk from a pre-Snow Leopard OS, the haphazard of data loss is small, even if you run or copy one of the files.

    The resource fork isn't the only position where Apple has decided to smuggle compressed data. For smaller files, hfsdebug shows the following:

    % hfsdebug /etc/asl.conf ... compression magic = cmpf compression sort = 3 (xattr has compressed data) uncompressed size = 860 bytes

    Here, the data is tiny enough to exist stored entirely within an extended attribute, albeit in compressed form. And then, the final frontier:

    % hfsdebug /Volumes/Snow Time/Applications/Mail.app/Contents/PkgInfo ... compression magic = cmpf compression sort = 3 (xattr has inline data) uncompressed size = 8 bytes

    That's right, an entire file's contents stored uncompressed in an extended attribute. In the case of a gauge PkgInfo file like this one, those contents are the four-byte classic Mac OS sort and creator codes.

    % xattr -l Applications/Mail.app/Contents/PkgInfo com.apple.decmpfs: 0000 66 70 6D 63 03 00 00 00 08 00 00 00 00 00 00 00 fpmc............ 0010 FF 41 50 50 4C 65 6D 61 6C .APPLemal

    There's soundless the selfsame "fpmc..." preamble seen in complete the earlier examples of the com.apple.decmpfs attribute, but at the terminate of the value, the expected data appears as unostentatious as day: sort code "APPL" (application) and creator code "emal" (for the Mail application—cute, as per classic Mac OS tradition).

    You may exist wondering, if this is complete about data compression, how does storing eight uncompressed bytes plus a 17-byte preamble in an extended ascribe save any disk space? The retort to that lies in how HFS+ allocates disk space. When storing information in a data or resource fork, HFS+ allocates space in multiples of the file system's allocation block size (4 KB, by default). So those eight bytes will Take up a minimum of 4,096 bytes if stored in the traditional way. When allocating disk space for extended attributes, however, the allocation block size is not a factor; the data is packed in much more tightly. In the end, the actual space saved by storing those 25 bytes of data in an extended ascribe is over 4,000 bytes.

    But compression isn't just about saving disk space. It's also a classic sample of trading CPU cycles for decreased I/O latency and bandwidth. Over the past few decades, CPU performance has gotten better (and computing resources more plentiful—more on that later) at a much faster rate than disk performance has increased. Modern difficult disk search times and rotational delays are soundless measured in milliseconds. In one millisecond, a 2 GHz CPU goes through two million cycles. And then, of course, there's soundless the actual data transfer time to consider.

    Granted, several levels of caching throughout the OS and hardware labor mightily to cloak these delays. But those bits possess to approach off the disk at some point to fill those caches. Compression means that fewer bits possess to exist transferred. Given the almost comical glut of CPU resources on a modern multi-core Mac under household use, the total time needed to transfer a compressed payload from the disk and expend the CPU to decompress its contents into reminiscence will soundless usually exist far less than the time it'd Take to transfer the data in uncompressed form.

    That explains the potential performance benefits of transferring less data, but the expend of extended attributes to store file contents can actually accomplish things faster, as well. It complete has to achieve with data locality.

    If there's one thing that slows down a difficult disk more than transferring a large amount of data, it's affecting its heads from one section of the disk to another. Every run means time for the head to start moving, then stop, then ensure that it's correctly positioned over the desired location, then wait for the spinning disk to set the desired bits beneath it. These are complete real, physical, affecting parts, and it's fabulous that they achieve their dance as quickly and efficiently as they do, but physics has its limits. These motions are the real performance killers for rotational storage like difficult disks.

    The HFS+ volume format stores complete its information about files—metadata—in two primary locations on disk: the Catalog File, which stores file dates, permissions, ownership, and a host of other things, and the Attributes File, which stores "named forks."

    Extended attributes in HFS+ are implemented as named forks in the Attributes File. But unlike resource forks, which can exist very large (up to the maximum file size supported by the file system), extended attributes in HFS+ are stored "inline" in the Attributes File. In practice, this means a restrict of about 128 bytes per attribute. But it also means that the disk head doesn't need to Take a trip to another section of the disk to acquire the actual data.

    As you can imagine, the disk blocks that accomplish up the Catalog and Attributes files are frequently accessed, and therefore more likely than most to exist in a cache somewhere. complete of this conspires to accomplish the complete storage of a file, including both its metadata in its data, within the B-tree-structured Catalog and Attributes files an overall performance win. Even an eight-byte payload that balloons to 25 bytes is not a concern, as long as it's soundless less than the allocation block size for household data storage, and as long as it complete fits within a B-tree node in the Attributes File that the OS has to read in its entirety anyway.

    There are other significant contributions to Snow Leopard's reduced disk footprint (e.g., the removal of unnecessary localizations and "designable.nib" files) but HFS+ compression is by far the most technically interesting.

    Installer intelligence

    Apple makes two other gripping promises about the installation process:

    Snow Leopard checks your applications to accomplish positive they're compatible and sets aside any programs known to exist incompatible. In case a power outage interrupts your installation, it can start again without losing any data.

    The setting aside of "known incompatible" applications is undoubtedly a response to the "blue screen" problems some users encountered when upgrading from Tiger to Leopard two years ago, which was caused by the presence of incompatible—and some would philosophize "illicit"—third-party system extensions. I possess a decidedly pragmatic view of such software, and I'm joyous to see Apple taking a similarly practical approach to minimizing its repercussion on users.

    Apple can't exist expected to detect and disable complete potentially incompatible software, of course. I suspect only the most approved or highest profile risky software is detected. If you're a developer, this installer feature may exist a top-notch passage to find out if you're on Apple's sh*t list.

    As for continuing an installation after a power failure, I didn't possess the guts to test this feature. (I also possess a UPS.) For long-running processes like installation, this kindly of added robustness is welcome, especially on battery-powered devices like laptops.

    I mention these two details of the installation process mostly because they highlight the kinds of things that are feasible when developers at Apple are given time to polish their respective components of the OS. You might reflect that the installer team would exist hard-pressed to approach up with enough to achieve during a nearly two-year development cycle. That's clearly not the case, and customers will gleam the benefits.

    Snow Leopard's novel looks

    I've long yearned for Apple to accomplish a cleanly break, at least visually, from Mac OS X's Aqua past. Alas, I will exist waiting a bit longer, because Snow Leopard ushers in no such revolution. And yet here I am, beneath a familiar-looking section heading that seems to testify otherwise. The veracity is, Snow Leopard actually changes the appearance of nearly every pixel on your screen—but not in the passage you might imagine.

    Since the dawn of color on the Macintosh, the operating system has used a default output gamma correction value of 1.8. Meanwhile, Windows—aka the repose of the world—has used a value of 2.2. Though this may not seem significant to anyone but professional graphics artists, the variation is usually unostentatious to even a casual observer when viewing the selfsame image on both kinds of displays side by side.

    Though Mac users will probably instinctively prefer the 1.8 gamma image that they're used to, Apple has decided that this historical variation is more cataclysm than it's worth. The default output gamma correction value in Snow Leopard is now 2.2, just like everyone else. Done and done.

    If they notice at all, users will likely experience this change as a emotion that the Snow Leopard user interface has a bit more contrast than Leopard's. This is reinforced by the novel default desktop background, a re-drawn, more saturated version of Leopard's default desktop. (Note that these are two entirely different images and not an attempt to demonstrate the effects of different gamma correction settings.)

    LeopardLeopard Snow LeopardSnow Leopard Dock Exposé spotlight effectDock Exposé spotlight effect

    But even beyond color correction, exact to form, Apple could not resist adding a few graphical tweaks to the Snow Leopard interface. The most unostentatious changes are related to the Dock. First, there's the novel "spotlight" peek triggered by a click-and-hold on an application icon in the Dock. (This activates Exposé, but only for the windows belonging to the application that was clicked. More later.)

    Furthermore, any and complete pop-up menus on the Dock—and only on the Dock—have a unique peek in Snow Leopard, complete with a custom selection appearance (which, for a change, does a passable job of matching the system-wide selection appearance setting).

    New Dock menu appearance. Mmmm… arbitrary.New Dock menu appearance. Mmmm… arbitrary.

    For Mac users of a unavoidable age, these menus may bring to intellect Apple's Hi-Tech appearance theme from the bad-old days of Copland. They're actually considerably more subtle, however. Note the translucent edges which accentuate the rounded corners. The gradient on the selection highlight is also admirably restrained.

    Nevertheless, this is an entirely novel peek for a lone (albeit commonly used) application, and it does clash a bit with the default "slanty, shiny shelf" appearance of the Dock. But I've already had my philosophize about that, and more. If the oath of Snow Leopard's appearance was to "first, achieve no harm," then I reflect I'm inclined to give it a passing grade—almost.

    If I had to characterize what's wrong with Snow Leopard's visual additions with just two words, it'd exist these: everything fades. Apple has sprinkled Core Animation fairy dust over seemingly every application in Snow Leopard. If any section of the user interface appears, disappears, or changes in any significant way, it's accompanied by an animation and one or more fades.

    In moderation, such effects are fine. But in several instances, Snow Leopard crosses the line. Or rather, it crosses my line, which, it should exist noted, is located far inside the territories of Candy Land. Others with a much lower tolerance for animations who are already galled by the frippery in Leopard and earlier releases will find miniature to value in Snow Leopard's visual changes.

    The one that really drove me over the edge is the fussy miniature dance of the filename district that occurs in the Finder (surprise!) when renaming a file on the desktop. There's just something about so many cross-fades, color changes, and text offsets occurring so rapidly and concentrated into such a tiny district that makes me want to scream. And whether or not I'm actually waiting for these animations to finish before I can continue to expend my computer, it certainly feels that passage sometimes.

    Still, I must unenthusiastically predict that most household people (i.e., the ones who will not read this entire article) will either find these added visual touches delightful, or (much more likely) not notice them at all.


    Animation aside, the visual sameness of Snow Leopard presents a bit of a marketing challenge for Apple. Even beyond the obvious problem of how to promote an operating system upgrade with "no novel features" to consumers, there's the issue of how to acquire people to notice that this novel product exists at all.

    In the run-up to Snow Leopard's release, Apple stuck to a modified version of Leopard's outer space theme. It was in the keynote slideshows, on the WWDC banners, on the developer release DVDs, and complete over the Mac OS X section of Apple's website. The header image from Apple's Mac OS X webpage as of a week before Snow Leopard's release appears below. It's pretty nick and dried: outer space, stars, affluent purple nebula, lens flare.

    Snow. The final frontier.Snow. The final frontier.

    Then came the golden master of Snow Leopard, which, in a pleasant change from past releases, was distributed to developers a few weeks before Snow Leopard hit the shelves. Its installer introduced an entirely different peek which, as it turns out, was carried over to the retail packaging. For a change, let's line up the discs instead of the packaging (which is rapidly shrinking to barely pen the disc anyway). Here's Mac OS X 10.0 through 10.6, top to bottom and left to right. (The 10.0 and 10.1 discs looked essentially identical and possess been coalesced.)

    One of these things is not like the others…One of these things is not like the others…

    Yep, it's a snow leopard. With actual snow on it. It's a bit on the nose for my taste, but it's not without its charms. And it does possess one titanic thing going for it: it's immediately recognizable as something novel and different. "Unmistakable" is how I'd sum up the packaging. Eight years of the giant, centered, variously adorned "X" and then boom: a cat. There's miniature haphazard that anyone who's seen Leopard sitting on the shelf of their local Apple store for the past two years will fail to notice that this is a novel product.

    (If you'd like your own picture of Snowy the snow leopard (that's right, I've named him), Apple was kindly enough to involve a desktop background image with the OS. Self-loathing Windows users may download it directly.)

    Warning: internals ahead

    We've arrived at the start of the customary "internals" section. Snow Leopard is complete about internal changes, and this is reflected in the content of this review. If you're only interested in the user-visible changes, you can skip ahead, but you'll exist missing out on the meat of this review and the heart of Apple's novel OS.

    64-bit: the road leads ever on

    Mac OS X started its journey to 64-bit back in 2003 with the release of Panther, which included the bare minimum back for the then-new PowerPC G5 64-bit CPU. In 2005, Tiger brought with it the skill to create exact 64-bit processes—as long as they didn't link with any of the GUI libraries. Finally, Leopard in 2007 included back for 64-bit GUI applications. But again, there was a caveat: 64-bit back extended to Cocoa applications only. It was, effectively, the terminate of the road for Carbon.

    Despite Leopard's seemingly impressive 64-bit bona fides, there are a few more steps before Mac OS X can gain complete 64-bit nirvana. The diagrams below illustrate.

    64-bit in Mac OS X 10.4 Tiger 64-bit in Mac OS X 10.5 Leopard 64-bit in Mac OS X 10.6 Snow Leopard Mac OS X 10.4 Tiger Mac OS X 10.5 Leopard Mac OS X 10.6 Snow Leopard

    As we'll see, complete that yellow in the Snow Leopard diagram represents its capability, not necessarily its default mode of operation.


    Snow Leopard is the first version of Mac OS X to ship with a 64-bit kernel ("K64" in Apple's parlance), but it's not enabled by default on most systems. The understanding for this this is simple. Recall that there's no "mixed mode" in Mac OS X. At runtime, a process is either 32-bit or 64-bit, and can only load other code—libraries, plug-ins, etc.—of the selfsame kind.

    An necessary class of plug-ins loaded by the kernel is device drivers. Were Snow Leopard to default to the 64-bit kernel, only 64-bit device drivers would load. And seeing as Snow Leopard is the first version of Mac OS X to involve a 64-bit kernel, there'd exist precious few of those on customers' systems on launch day.

    And so, by default, Snow Leopard boots with a 64-bit kernel only on Xserves from 2008 or later. I guess the assumption is that complete of the devices commonly attached to an Xserve will exist supported by 64-bit drivers supplied by Apple in Snow Leopard itself.

    Perhaps surprisingly, not complete Macs with 64-bit processors are even able to boot into the 64-bit kernel. Though this may change in subsequent point releases of Snow Leopard, the table below lists complete the Macs that are either capable of or default to booting K64. (To find the "Model name" of your Mac, select "About This Mac" from the Apple menu, then click the "More info…" button and read the "Model Identifier" line in the window that appears.)

    Product Model name K64 status Early 2008 Mac Pro MacPro3,1 Capable Early 2008 Xserve Xserve2,1 Default MacBook Pro 15"/17" MacBookPro4,1 Capable iMac iMac8,1 Capable UniBody MacBook Pro 15" MacBookPro5,1 Capable UniBody MacBook Pro 17" MacBookPro5,2 Capable Mac Pro MacPro4,1 Capable iMac iMac9,1 Capable Early 2009 Xserve Xserve3,1 Default

    For complete K64-capable Macs, boot while holding down "6" and "4" keys simultaneously to select the 64-bit kernel. For a more permanent solution, expend the nvram command to add arch=x86_64 to your boot-args string, or edit the file /Library/Preferences/SystemConfiguration/com.apple.Boot.plist and add arch=x86_64 to the Kernel Flags string:

    ... <key>Kernel</key> <string>mach_kernel</string> <key>Kernel Flags</key> <string>arch=x86_64</string> ...

    To switch back to the 32-bit kernel, hold down the "3" and "2" keys during boot, or expend one of the techniques above, replacing "x86_64" with "i386".

    We've already discussed why, at least initially, you probably won't want to boot into K64. But as Snow Leopard adoption ramps up and 64-bit updates of existing kernel extensions become available, why might you actually want to expend the 64-bit kernel?

    The first understanding has to achieve with RAM, and not in the passage you might think. Though Leopard uses a 32-bit kernel, Macs running Leopard can contain and expend far more RAM than the 4 GB restrict the "32-bit" qualifier might seem to imply. But as RAM sizes increase, there's another concern: address space depletion—not for applications, but for the kernel itself.

    As a 32-bit process, the kernel itself is limited to a 32-bit (i.e., 4GB) address space. That may not seem like a problem; after all, should the kernel really need more than 4GB of reminiscence to achieve its job? But recollect that section of the kernel's job is to track and manage system memory. The kernel uses a 64-byte structure to track the status of each 4KB page of RAM used on the system.

    That's 64 bytes, not kilobytes. It hardly seems like a lot. But now admiration a Mac in the not-too-distant future containing 96GB of RAM. (If this sounds ridiculous to you, reflect of how ridiculous the 8GB of RAM in the Mac I'm typing on perquisite now would possess sounded to you five years ago.) Tracking 96GB of RAM requires 1.5GB of kernel address space. Using more than a third of the kernel's address space just to track reminiscence is a pretty uncomfortable situation.

    A 64-bit kernel, on the other hand, has a virtually unlimited kernel address space (16 exabytes). K64 is an inevitable necessity, given the rapidly increasing size of system memory. Though you may not need it today on the desktop, it's already common for servers to possess double-digit gigabytes of RAM installed.

    The other thing K64 has going for it is speed. The x86 instruction set architecture has had a bit of a tortured history. When designing the x86-64 64-bit extension of the x86 architecture, AMD took the occasion to leave behind some of the ugliness of the past and involve more modern features: more registers, novel addressing modes, non-stack-based floating point capabilities, etc. K64 reaps these benefits. Apple makes the following claims about its performance:

  • 250% faster system convoke entry point
  • 70% faster user/kernel reminiscence copy
  • Focused benchmarking would endure these out, I'm sure. But in daily use, you're unlikely to exist able to ascribe any particular performance boost to the kernel. reflect of K64 as removing bottlenecks from the few (usually server-based) applications that actually achieve exercise these aspects of the kernel heavily.

    If it makes you feel better to know that your kernel is operating more efficiently, and that, were you to actually possess 96GB of RAM installed, you would not risk starving the kernel of address space, and if you don't possess any 32-bit drivers that you absolutely need to use, then by complete means, boot into the 64-bit kernel.

    For everyone else, my advice is to exist joyous that K64 will exist ready and waiting for you when you eventually achieve need it—and gratify achieve embolden complete the vendors that accomplish kernel extensions that you custody about to add K64 back as soon as possible.

    Finally, this is worth repeating: gratify retain in intellect that you achieve not need to accelerate the 64-bit kernel in order to accelerate 64-bit applications or install more than 4GB of RAM in your Mac. Applications accelerate just fine in 64-bit mode on top of the 32-bit kernel, and even in earlier versions of Mac OS X it's been feasible to install and Take advantage of much more than 4GB of RAM.

    64-bit applications

    While Leopard may possess brought with it back for 64-bit GUI applications, it actually included very few of them. In fact, by my count, only two 64-bit GUI applications shipped with Leopard: Xcode (an optional install) and Chess. And though Leopard made it feasible for third-party developers to capitulate 64-bit (albeit Leopard-only) GUI applications, very few have—sometimes due to luckless realities, but most often because there's been no top-notch understanding to achieve so, abandoning users of Mac OS X 10.4 or earlier in the process.

    Apple is now pushing the 64-bit transition much harder. This starts with leading by example. Snow Leopard ships with four end-user GUI applications that are not 64-bit: iTunes, Grapher, Front Row, and DVD Player. Everything else is 64-bit. The Finder, the Dock, Mail, TextEdit, Safari, iChat, Address Book, Dashboard, abet Viewer, Installer, Terminal, Calculator—you cognomen it, it's 64-bit.

    The second titanic carrot (or stick, depending on how you peek at it) is the continued lack of 32-bit back for novel APIs and technologies. Leopard started the trend, leaving deprecated APIs behind and only porting the novel ones to 64-bit. The improved Objective-C 2.0 runtime introduced in Leopard was also 64-bit-only.

    Snow Leopard continues along similar lines. The Objective-C 2.1 runtime's non-fragile instance variables, exception model unified with C++, and faster vtable dispatch remain available only to 64-bit applications. But the most significant novel 64-bit-only API is QuickTime X—significant enough to exist addressed separately, so stay tuned.

    64-bits or bust

    All of this is Apple's not-so-subtle passage of telling developers that the time to run to 64-bit is now, and that 64-bit should exist the default for complete novel applications, whether a developer thinks it's "needed" or not. In most cases, these novel APIs possess no intrinsic connection to 64-bit. Apple has simply chosen to expend them as additional forms of persuasion.

    Despite complete of the above, I'd soundless convoke Snow Leopard merely the penultimate step in Mac OS X's journey to exist 64-bit from top to bottom. I fully anticipate Mac OS X 10.7 to boot into the 64-bit kernel by default, to ship with 64-bit versions of complete applications, plug-ins, and kernel extensions, and to leave even more legacy and deprecated APIs to fade away in the land of 32-bit.

    QuickTime X

    Apple did something a bit odd in Leopard when it neglected to port the C-based QuickTime API to 64-bit. At the time, it didn't seem like such a titanic deal. Mac OS X's transition to 64-bit had already spanned many years and several major versions. One could imagine that it just wasn't yet QuickTime's turn to proceed 64-bit.

    As it turns out, my terse but pessimistic assessment of the situation at the time was accurate: QuickTime got the "Carbon treatment". like Carbon, the venerable QuickTime API that they know and value will not exist making the transition to 64-bit—ever.

    To exist clear, QuickTime the technology and QuickTime the brand will most definitely exist coming to 64-bit. What's being left behind in 32-bit-only profile is the C-based API introduced in 1991 and built upon for 18 years thereafter. Its replacement in the world of 64-bit in Snow Leopard is the aptly named QuickTime X.

    The "X" in QuickTime X, like the one in in Mac OS X, is pronounced "ten." This is but the first of many eerie parallels. like Mac OS X before it, QuickTime X:

  • aims to accomplish a cleanly fracture from its predecessor
  • is based on technology originally developed for another platform
  • includes transparent compatibility with its earlier incarnation
  • promises better performance and a more modern architecture
  • lacks many necessary features in its initial release
  • Maximum available Mac CPU  accelerate (MHz)Maximum available Mac CPU accelerate (MHz)

    Let's Take these one at a time. First, why is a cleanly fracture needed? set simply, QuickTime is old—really old. The horribly blocky, postage-stamp-size video displayed by its initial release in 1991 was considered a technological tour de force.

    At the time, the fastest Macintosh money could buy contained a 25 MHz CPU. The ridiculous chart to the perquisite is meant to hammer home this point. Forward-thinking design can only acquire you so far. The shape of the world a technology is born into eventually, inevitably dictates its fate. This is especially exact for long-lived APIs like QuickTime with a tough bent towards backward compatibility.

    As the first successful implementation of video on a personal computer, it's frankly fabulous that the QuickTime API has lasted as long as it has. But the world has moved on. Just as Mac OS establish itself mired in a ghetto of cooperative multitasking and unprotected memory, QuickTime limps into 2009 with antiquated notions of concurrency and subsystem layering baked into its design.

    When it came time to write the video-handling code for the iPhone, the latest version of QuickTime, QuickTime 7, simply wasn't up to the task. It had grown too bloated and inefficient during its life on the desktop, and it lacked top-notch back for the GPU-accelerated video playback necessary to wield modern video codecs on a handheld (even with a CPU sixteen times the clock accelerate of any available in a Mac when QuickTime 1.0 was released). And so, Apple created a tight, modern, GPU-friendly video playback engine that could appropriate comfortably within the RAM and CPU constraints of the iPhone.

    Hmm. An aging desktop video API in need of a replacement. A fresh, novel video library with top-notch performance even on (comparatively) anemic hardware. Apple connected the dots. But the trick is always in the transition. Happily, this is Apple's forte. QuickTime itself has already lived on three different CPU architectures and three entirely different operating systems.

    The switch to 64-bit is yet another (albeit less dramatic) inflection point, and Apple has chosen it to stamp the boundary between the aged QuickTime 7 and the novel QuickTime X. It's done this in Snow Leopard by limiting complete expend of QuickTime by 64-bit applications to the QTKit Objective-C framework.

    QTKit's novel world order

    QTKit is not new; it began its life in 2005 as a more native-feeling interface to QuickTime 7 for Cocoa applications. This extra layer of abstraction is the key to the QuickTime X transition. QTKit now hides within its object-oriented walls both QuickTime 7 and QuickTime X. Applications expend QTKit as before, and behind the scenes QTKit will elect whether to expend QuickTime 7 or QuickTime X to fulfill each request.

    If QuickTime X is so much better, why doesn't QTKit expend it for everything? The retort is that QuickTime X, like its Mac OS X namesake, has very limited capabilities in its initial release. While QuickTime X supports playback, capture, and exporting, it does not back general-purpose video editing. It also supports only "modern" video formats—basically, anything that can exist played by an iPod, iPhone, or Apple TV. As for other video codecs, well, you can forget about handling them with plug-ins because QuickTime X doesn't back those either.

    For every one of the cases where QuickTime X is not up to the job, QuickTime 7 will fill in. Cutting, copying, and pasting portions of a video? QuickTime 7. Extracting individual tracks from a movie? QuickTime 7. Playing any movie not natively supported by an existing Apple handheld device? QuickTime 7. Augmenting QuickTime's codec back using a plug-in of any kind? You guessed it: QuickTime 7.

    But wait a second. If QTKit is the only passage for a 64-bit application to expend QuickTime, and QTKit multiplexes between QuickTime 7 and QuickTime X behind the scenes, and QuickTime 7 is 32-bit-only, and Mac OS X does not back "mixed mode" processes that can execute both 32-bit and 64-bit code, then how the heck does a 64-bit process achieve anything that requires the QuickTime 7 back-end?

    To find out, fire up the novel 64-bit QuickTime Player application (which will exist addressed separately later) and open a movie that requires QuickTime 7. Let's say, one that uses the Sorenson video codec. (Remember that? top-notch times.) positive enough, it plays just fine. But search for "QuickTime" in the Activity Monitor application and you'll see this:

    Pretty sneaky, sis: 32-bit QTKitServer processPretty sneaky, sis: 32-bit QTKitServer process

    And the retort is revealed. When a 64-bit application using QTKit requires the services of the 32-bit-only QuickTime 7 back-end, QTKit spawns a divorce 32-bit QTKitServer process to achieve the labor and communicate the results back to the originating 64-bit process. If you leave Activity Monitor open while using the novel QuickTime Player application, you can watch the QTKitServer processes approach and proceed as needed. This is complete handled transparently by the QTKit framework; the application itself need not exist aware of these machinations.

    Yes, it's going to exist a long, long time before QuickTime 7 disappears completely from Mac OS X (at least Apple was kindly enough not to convoke it "QuickTime Classic"), but the path forward is clear. With each novel release of Mac OS X, anticipate the capabilities of QuickTime X to expand, and the number of things that soundless require QuickTime 7 to decrease. In Mac OS X 10.7, for example, I imagine that QuickTime X will gain back for plug-ins. And surely by Mac OS X 10.8, QuickTime X will possess complete video editing support. complete this will exist happening beneath the unifying facade of QTKit until, eventually, the QuickTime 7 back-end is no longer needed at all.

    Say what you mean

    In the meantime, perhaps surprisingly, many of the current limitations of QuickTime X actually highlight its unique advantages and inform the evolving QTKit API. Though there is no direct passage for a developer to request that QTKit expend the QuickTime X back-end, there are several roundabout means to influence the decision. The key is the QTKit API, which relies heavily on the concept of intent.

    QuickTime versions 1 through 7 expend a lone representation of complete media resources internally: a Movie object. This representation includes information about the individual tracks that accomplish up the movie, the sample tables for each track, and so on—all the information QuickTime needs to understand and maneuver the media.

    This sounds much until you realize that to achieve anything with a media resource in QuickTime requires the construction of this comprehensive Movie object. admiration playing an MP3 file with QuickTime, for example. QuickTime must create its internal Movie protest representation of the MP3 file before it can start playback. Unfortunately, the MP3 container format seldom contains comprehensive information about the structure of the audio. It's usually just a stream of packets. QuickTime must laboriously scan and parse the entire audio stream in order to complete the Movie object.

    QuickTime 7 and earlier versions accomplish this process less painful by doing the scanning and parsing incrementally in the background. You can see this in many QuickTime-based player applications in the profile of a progress bar overlaid on the movie controller. The image below shows a 63MB MP3 podcast loading in the Leopard version of QuickTime Player. The shaded portion of the movie timeline slowly fills the dotted district from left to right.

    QuickTime 7 doing more  labor than necessary

    QuickTime 7 doing more labor than necessary

    Though playback can start almost immediately (provided you play from the beginning, that is) it's worthwhile to Take a step back and admiration what's going on here. QuickTime is creating a Movie protest suitable for any operation that QuickTime can perform: editing, track extraction or addition, exporting, you cognomen it. But what if complete I want to achieve is play the file?

    The cataclysm is, the QuickTime 7 API lacks a passage to express this kindly of intent. There is no passage to philosophize to QuickTime 7, "Just open this file as quickly as feasible so that I can play it. Don't bother reading every lone byte of the file from the disk and parsing it to determine its structure just in case I resolve to edit or export the content. That is not my intent. Please, just open it for playback."

    The QTKit API in Snow Leopard provides exactly this capability. In fact, the only passage to exist eligible for the QuickTime X back-end at complete is to explicitly express your intent not to achieve anything QuickTime X cannot handle. Furthermore, any attempt to perform an operation that lies outside your previously expressed intent will understanding QTKit to raise an exception.

    The intent mechanism is also the passage that the novel features of QuickTime X are exposed, such as the skill to asynchronously load large or distantly located (e.g., over a unhurried network link) movie files without blocking the UI running on the main thread of the application.

    Indeed, there are many reasons to achieve what it takes to acquire on board the QuickTime X train. For the media formats it supports, QuickTime X is less taxing on the CPU during playback than QuickTime 7. (This is beyond the fact that QuickTime X does not blow time preparing its internal representation of the movie for editing and export when playback is complete that's desired.) QuickTime X also supports GPU-accelerated playback of H.264, but, in this initial release, only on Macs equipped with an NVIDIA 9400M GPU (i.e., some 2009 iMacs and several models of MacBooks from 2008 and 2009). Finally, QuickTime X includes comprehensive ColorSync back for video, which is long overdue.

    The X factor

    This is just the start of a long journey for QuickTime X, and seemingly not a very auspicious one, at that. A QuickTime engine with no editing support? No plug-ins? It seems ridiculous to release it at all. But this has been Apple's passage in recent years: steady, deliberate progress. Apple aims to ship no features before their time.

    As anxious as developers may exist for a full-featured, 64-bit successor to the QuickTime 7 engine, Apple itself is sitting on top of one of the largest QuickTime-riddled (and Carbon-addled, to boot) code bases in the industry: Final nick Studio. Thus far, It remains stuck in 32-bit. To philosophize that Apple is "highly motivated" to extend the capabilities of QuickTime X would exist an understatement.

    Nevertheless, don't anticipate Apple to rush forward foolishly. Duplicating the functionality of a continually developed, 18-year-old API will not betide overnight. It will Take years, and it will exist even longer before every necessary Mac OS X application is updated to expend QTKit exclusively. Transitions. Gotta value 'em.

    File system API unification

    Mac OS X has historically supported many different ways of referring to files on disk from within an application. Plain-old paths (e.g., /Users/john/Documents/myfile) are supported at the lowest levels of the operating system. They're simple, predictable, but perhaps not such a much concept to expend as the only passage an application tracks files. admiration what happens if an application opens a file based on a path string, then the user moves that file somewhere else while it's soundless being edited. When the application is instructed to save the file, if it only has the file path to labor with, it will terminate up creating a novel file in the aged location, which is almost certainly not what the user wanted.

    Classic Mac OS had a more sophisticated internal representation of files that enabled it to track files independent of their actual locations on disk. This was done with the abet of the unique file ids supported by HFS/HFS+. The Mac OS X incarnation of this concept is the FSRef data type.

    Finally, in the modern age, URLs possess become the de facto representation for files that may exist located somewhere other than the local machine. URLs can also advert to local files, but in that case they possess complete the selfsame disadvantages as file paths.

    This diversity of data types is reflected in Mac OS X's file system APIs. Some functions Take file path as arguments, some anticipate opaque references to files, and soundless others labor only with URLs. Programs that expend these APIs often disburse a lot of their time converting file references from one representation to another.

    The situation is similar when it comes to getting information about files. There are a huge number of file system metadata retrieval functions at complete levels of the operating system, and no lone one of them is comprehensive. To acquire complete available information about a file on disk requires making several divorce calls, each of which may anticipate a different sort of file reference as an argument.

    Here's an sample Apple provided at WWDC. Opening a lone file in the Leopard version of the Preview image viewer application results in:

  • Four conversions of an FSRef to a file path
  • Ten conversions of a file path to an FSRef
  • Twenty-five calls to getattrlist()
  • Eight calls to stat()/lstat()
  • Four calls to open()/close()
  • In Snow Leopard, Apple has created a new, unified, comprehensive set of file system APIs built around a lone data type: URLs. But these are URL "objects"—namely, the opaque data types NSURL and CFURL, with a toll-free bridge between them—that possess been imbued with complete the desirable attributes of an FSRef.

    Apple settled on these data types because their opaque nature allowed this kindly of enhancement, and because there are so many existing APIs that expend them. URLs are also the most future-proof of complete the choices, with the scheme portion providing nearly unlimited flexibility for novel data types and access mechanisms. The novel file system APIs built around these opaque URL types back caching and metadata prefetching for a further performance boost.

    There's also a novel on-disk representation called a Bookmark (not to exist confused with a browser bookmark) which is like a more network-savvy replacement for classic Mac OS aliases. Bookmarks are the most robust passage to create a reference to a file from within another file. It's also feasible to attach whimsical metadata to each Bookmark. For example, if an application wants to retain a persistent list of "favorite" files plus some application-specific information about them, and it wants to exist resilient to any movement of these files behind its back, Bookmarks are the best implement for the job.

    I mention complete of this not because I anticipate file system APIs to exist complete that gripping to people without my particular fascination with this section of the operating system, but because, like Core Text before it, it's an indication of exactly how immature Mac OS X really is as a platform. Even after seven major releases, Mac OS X is soundless struggling to run out from the shadow of its three ancestors: NeXTSTEP, classic Mac OS, and BSD Unix. Or perhaps it just goes to define how ruthlessly Apple's core OS team is driven to supersede aged and crusty APIs and data types with new, more modern versions.

    It will exist a long time before the benefits of these changes trickle down (or is it up?) to end-users in the profile of Mac applications that are written or modified to expend these novel APIs. Most well-written Mac applications already exhibit most of the desirable behavior. For example, the TextEdit application in Leopard will correctly detect when a file it's working on has moved.

    TextEdit: a  top-notch Mac OS X citizenTextEdit: a top-notch Mac OS X citizen

    Of course, the key modifier here is "well-written." Simplifying the file system APIs means that more developers will exist willing to expend the effort—now greatly reduced—to provide such user-friendly behaviors. The accompanying performance boost is just icing on the cake, and one more understanding that developers might elect to alter their existing, working application to expend these novel APIs.

    Doing more with more

    Moore's Law is widely cited in technology circles—and also widely misunderstood. It's most often used as shorthand for "computers double in accelerate every year or so," but that's not what Gordon Moore wrote at all. His 1965 article in Electronics magazine touched on many topics in the semiconductor industry, but if it had to exist summed up in a lone "law", it would be, roughly, that the number of transistors that appropriate onto a square inch of silicon doubles every 12 months.

    Moore later revised that to two years, but the time age is not what people acquire wrong. The problem is confusing a doubling of transistor density with a doubling of "computer speed." (Even more problematic is declaring a "law" based on a lone paper from 1965, but we'll set that aside for now. For a more thorough discussion of Moore's Law, gratify read this classic article by Jon Stokes.)

    For decades, each augment in transistor density was, in fact, accompanied by a comparable augment in computing accelerate thanks to ever-rising clock speeds and the dawn of superscalar execution. This worked great—existing code ran faster on each novel CPU—until the grim realities of power density set an terminate to the fun.

    Moore's Law continues, at least for now, but their skill to accomplish code accelerate faster with each novel augment in transistor density has slowed considerably. The free lunch is over. CPU clock speeds possess stagnated for years, many times actually going backwards. (The latest top-of-the-line 2009 Mac Pro contains a 2.93 GHz CPU, whereas the 2008 model could exist equipped with a 3.2 GHz CPU.) Adding execution units to a CPU has also long since reached the point of diminishing returns, given the limits of instruction-level parallelism in common application code.

    And yet we've soundless got complete these novel transistors raining down on us, more every year. The challenge is to find novel ways to expend them to actually accomplish computers faster.

    Thus far, the semiconductor industry's retort has been to give us more of what they already have. Where once a CPU contained a lone logical processing unit, now CPUs in even the lowliest desktop computers contain two processor cores, with high-end models sporting two chips with eight logical cores each. Granted, the cores themselves are also getting faster, usually by doing more at the selfsame clock accelerate as their predecessors, but that's not happening at nearly the rate that the cores are multiplying.

    Unfortunately, generally speaking, a dual-core CPU will not accelerate your application twice as rapidly as a single-core CPU. In fact, your application probably won't accelerate any faster at complete unless it was written to Take advantage of more than just a lone logical CPU. Presented with a glut of transistors, chipmakers possess turned around and provided more computing resources than programmers know what to achieve with, transferring much of the responsibility for making computers faster to the software guys.

    We're with the operating system and we're here to help

    It's into this environment that Snow Leopard is born. If there's one responsibility (aside from security) that an operating system vendor should feel in the year 2009, it's finding a passage for applications—and the OS itself—to utilize the ever-growing wealth of computing resources at their disposal. If I had to pick lone technological "theme" for Snow Leopard, this would exist it: helping developers utilize complete this newfound silicon; helping them achieve more with more.

    To that end, Snow Leopard includes two significant novel APIs backed by several smaller, but equally necessary infrastructure improvements. We'll start at the bottom with, believe it or not, the compiler.

    LLVM and Clang

    Apple made a strategic investment in the LLVM open source project several years ago. I covered the fundamentals of LLVM in my Leopard review. (If you're not up to speed, gratify enmesh up on the topic before continuing.) In it, I described how Leopard used LLVM to provide dramatically more efficient JIT-compiled software implementations of OpenGL functions. I ended with the following admonition:

    Don't exist misled by its humble expend in Leopard; Apple has imposing plans for LLVM. How grand? How about swapping out the guts of the gcc compiler Mac OS X uses now and replacing them with the LLVM equivalents? That project is well underway. Not ambitious enough? How about ditching gcc entirely, replacing it with a completely novel LLVM-based (but gcc-compatible) compiler system? That project is called Clang, and it's already yielded some impressive performance results.

    With the introduction of Snow Leopard, it's official: Clang and LLVM are the Apple compiler strategy going forward. LLVM even has a snazzy novel logo, a not-so-subtle homage to a well-known compiler design textbook:

    LLVM! Clang! Rawr!

    LLVM! Clang! Rawr!

    Apple now offers a total of four compilers for Mac OS X: GCC 4.0, GCC 4.2, LLVM-GCC 4.2 (the GCC 4.2 front-end combined with an LLVM back-end), and Clang, in order of increasing LLVM-ness. Here's a diagram:

    Mac OS X compilers

    Mac OS X compilers

    All of these compilers are binary-compatible on Mac OS X, which means you can, for example, build a library with one compiler and link it into an executable built with another. They're also complete command-line and source-compatible—in theory, anyway. Clang does not yet back some of the more esoteric features of GCC. Clang also only supports C, Objective-C, and a miniature bit of C++ (Clang(uage), acquire it?) whereas GCC supports many more. Apple is committed to complete C++ back for Clang, and hopes to labor out the remaining GCC incompatibilities during Snow Leopard's lifetime.

    Clang brings with it the two headline attributes you anticipate in a hot, novel compiler: shorter compile times and faster executables. In Apple's testing with its own applications such as iCal, Address Book, and Xcode itself, plus third-party applications like Adium and Growl, Clang compiles nearly three times faster than GCC 4.2. As for the accelerate of the finished product, the LLVM back-end, whether used in Clang or in LLVM-GCC, produces executables that are 5-25% faster than those generated by GCC 4.2.

    Clang is also more developer-friendly than its GCC predecessors. I concede that this topic doesn't possess much to achieve with taking advantage of multiple CPU cores and so on, but it's positive to exist the first thing that a developer actually notices when using Clang. Indulge me.

    For starters, Clang is embeddable, so Xcode can expend the selfsame compiler infrastructure for interactive features within the IDE (symbol look-up, code completion, etc.) as it uses to compile the final executable. Clang also creates and preserves more extensive metadata while compiling, resulting in much better mistake reporting. For example, when GCC tells you this:

    GCC  mistake message for an unknown type

    It's not exactly lucid what the problem is, especially if you're novel to C programming. Yes, complete you hotshots already know what the problem is (especially if you saw this sample at WWDC), but I reflect everyone can disagree that this error, generated by Clang, is a lot more helpful:

    Clang  mistake message for an unknown type

    Maybe a novice soundless wouldn't know what to do, but at least it's lucid where the problem lies. Figuring out why the compiler doesn't know about NSString is a much more focused chore than can exist derived from GCC's cryptic error.

    Even when the message is clear, the context may not be. Take this mistake from GCC:

    GCC  mistake message for  wrong operands

    Sure, but there are four "+" operators on that lone line. Which one has the problematic operands? Thanks to its more extensive metadata, Clang can pinpoint the problem:

    Clang  mistake message for  wrong operands

    Sometimes the mistake is perfectly clear, but it just seems a bit off, like this situation where jumping to the mistake as reported by GCC puts you on the line below where you actually want to add the missing semicolon:

    GCC  mistake message for missing semicolon

    The miniature things count, you know? Clang goes that extra mile:

    Clang  mistake message for missing semicolon

    Believe it or not, stuff like this means a lot to developers. And then there are the not-so-little things that spell even more, like the LLVM-powered static analyzer. The image below shows how the static analyzer displays its discovery of a feasible bug.

    OH HAI I  establish UR BUGOH HAI I establish UR BUG

    Aside from the whimsy of the miniature arrows (which, admit it, are adorable), the actual bug it's highlighting is something that every programmer can imagine creating (say, through some hasty editing). The static analyzer has determined that there's at least one path through this set of nested conditionals that leaves the myName variable uninitialized, thus making the attempt to send the mutableCopy message in the final line potentially dangerous.

    I'm positive Apple is going hog-wild running the static analyzer on complete of its applications and the operating system itself. The prospect of an automated passage to determine bugs that may possess existed for years in the depths of a huge codebase is almost pornographic to developers—platform owners in particular. To the degree that Mac OS X 10.6.0 is more bug-free than the previous 10.x.0 releases, LLVM surely deserves some significant section of the credit.

    Master of the house

    By committing to a Clang/LLVM-powered future, Apple has finally taken complete control of its development platform. The CodeWarrior experience apparently convinced Apple that it's unwise to dependence on a third party for its platform's development tools. Though it's taken many years, I reflect even the most diehard Metrowerks fan would possess to disagree that Xcode in Snow Leopard is now a pretty damn top-notch IDE.

    After years of struggling with the disconnect between the goals of the GCC project and its own compiler needs, Apple has finally nick the apron strings. OK, granted, GCC 4.2 is soundless the default compiler in Snow Leopard, but this is a transitional phase. Clang is the recommended compiler, and the focus of complete of Apple's future efforts.

    I know what you're thinking. This is swell and all, but how are these compilers helping developers better leverage the expanding swarm of transistors at their disposal? As you'll see in the following sections, LLVM's scaly, metallic head pops up in a few key places.


    In Snow Leopard, Apple has introduced a C language extension called "blocks." Blocks add closures and anonymous functions to C and the C-derived languages C++, Objective-C, and Objective C++.

    These features possess been available in dynamic programming languages such as Lisp, Smalltalk, Perl, Python, Ruby, and even the unassuming JavaScript for a long time (decades, in the case of Lisp—a fact gladly offered by its practitioners). While dynamic-language programmers Take closures and anonymous functions for granted, those who labor with more traditional, statically compiled languages such as C and its derivatives may find them quite exotic. As for non-programmers, they likely possess no interest in this topic at all. But I'm going to attempt an explanation nonetheless, as blocks profile the foundation of some other gripping technologies to exist discussed later.

    Perhaps the simplest passage to define blocks is that they accomplish functions another profile of data. C-derived languages already possess role pointers, which can exist passed around like data, but these can only point to functions created at compile time. The only passage to influence the behavior of such a role is by passing different arguments to the role or by setting global variables which are then accessed from within the function. Both of these approaches possess titanic disadvantages

    Passing arguments becomes cumbersome as their number and complexity grows. Also, it may exist that you possess limited control over the arguments that will exist passed to your function, as is often the case with callbacks. To compensate, you may possess to bundle up complete of your gripping state into a context protest of some kind. But when, how, and by whom that context data will exist disposed of can exist difficult to pin down. Often, a second callback is required for this. It's complete quite a pain.

    As for the expend of global variables, in addition to being a well-known anti-pattern, it's also not thread-safe. To accomplish it so requires locks or some other profile of mutual exclusion to obviate multiple invocations of the selfsame role from stepping on each other's toes. And if there's anything worse than navigating a sea of callback-based APIs, it's manually dealing with thread safety issues.

    Blocks bypass complete of these problems by allowing functional blobs of code—blocks—to exist defined at runtime. It's easiest to understand with an example. I'm going to start by using JavaScript, which has a bit friendlier syntax, but the concepts are the same.

    b = get_number_from_user(); multiplier = function(a) { recur a * b };

    Here I've created a role named multiplier that takes a lone argument, a, and multiplies it by a second value, b, that's provided by the user at runtime. If the user supplied the number 2, then a convoke to multiplier(5) would recur the value 10.

    b = get_number_from_user(); // assume it's 2 multiplier = function(a) { recur a * b }; r = multiplier(5); // 5 * 2 = 10

    Here's the sample above done with blocks in C.

    b = get_number_from_user(); // assume it's 2 multiplier = ^ int (int a) { recur a * b; }; r = multiplier(5); // 5 * 2 = 10

    By comparing the JavaScript code to the C version, I hope you can see how it works. In the C example, that miniature caret ^ is the key to the syntax for blocks. It's kindly of ugly, but it's very C-like in that it parallels the existing C syntax for role pointers, with ^ in position of *, as this sample illustrates:

    /* A role that takes a lone integer dispute and returns a pointer to a role that takes two integer arguments and returns a floating-point number. */ float (*func2(int a))(int, int); /* A role that takes a lone integer dispute and returns a block that takes two integer arguments and returns a floating-point number. */ float (^func1(int a))(int, int);

    You'll just possess to dependence me when I divulge you that this syntax actually makes sense to seasoned C programmers.

    Now then, does this spell that C is suddenly a dynamic, high-level language like JavaScript or Lisp? Hardly. The existing distinction between the stack and the heap, the rules governing automatic and static variables, and so on are complete soundless in complete effect. Plus, now there's a all novel set of rules for how blocks interact with each of these things. There's even a novel __block storage sort ascribe to further control the scope and lifetime of values used in blocks.

    All of that said, blocks are soundless a huge win in C. Thanks to blocks, the friendlier APIs long enjoyed by dynamic languages are now feasible in C-derived languages. For example, suppose you want to apply some operation to every line in a file. To achieve so in a low-level language like C requires some amount of boilerplate code to open and read from the file, wield any errors, read each line into a buffer, and cleanly up at the end.

    FILE *fp = fopen(filename, "r"); if (fp == NULL) { perror("Unable to open file"); } else { char line[MAX_LINE]; while (fgets(line, MAX_LINE, fp)) { work; work; work; } fclose(fp); }

    The section in bold is an abstract representation of what you're planning to achieve to each line of the file. The repose is the literal boilerplate code. If you find yourself having to apply varying operations to every line of many different files, this boilerplate code gets tedious.

    What you'd like to exist able to achieve is factor it out into a role that you can call. But then you're faced with the problem of how to express the operation you'd like to perform on each line of the file. In the middle of each block of boilerplate may exist many lines of code expressing the operation to exist applied. This code may reference or modify local variables which are affected by the runtime behavior of the program, so traditional role pointers won't work. What to do?

    Thanks to blocks, you can define a role that takes a filename and a block as arguments. This gets complete the uninteresting code out of your face.

    foreach_line(filename, ^ (char *line) { work; work; work; });

    What's left is a much clearer expression of your intent, with less surrounding noise. The dispute after filename is a literal block that takes a line of text as an argument.

    Even when the volume of boilerplate is small, the simplicity and clarity gratuity is soundless worthwhile. admiration the simplest feasible loop that executes a fixed number of times. In C-based languages, even that basic construct offers a surprising number of opportunities for bugs. Let's do_something() 10 times:

    for (int i = 0; i <= 10; i++) { do_something(); }

    Oops, I've got a miniature bug there, don't I? It happens to the best of us. But why should this code exist more complicated than the sentence describing it. achieve something 10 times! I never want to screw that up again. Blocks can help. If they just invest a miniature effort up front to define a helper function:

    typedef void (^work_t)(void); void repeat(int n, work_t block) { for (int i = 0; i < n; ++i) block(); }

    We can exile the bug for good. Now, repeating any whimsical block of code a specific number of times is complete but idiot-proof:

    repeat(10, ^{ do_something() }); repeat(20, ^{ do_other_thing() });

    And remember, the block dispute to repeat() can contain exactly the selfsame kindly of code, literally copied and pasted, that would possess appeared within a traditional for loop.

    All these possibilities and more possess been well explored by dynamic languages: map, reduce, collect, etc. Welcome, C programmers, to a higher order.

    Apple has taken these lessons to heart, adding over 100 novel APIs that expend blocks in Snow Leopard. Many of these APIs would not exist feasible at complete without blocks, and complete of them are more elegant and concise than they would exist otherwise.

    It's Apple goal to submit blocks as an official extension to one or more of the C-based languages, though it's not yet lucid which standards bodies are receptive to the proposal. For now, blocks are supported by complete four of Apple's compilers in Mac OS X.

    Concurrency in the real world: a prelude

    The struggle to accomplish efficient expend of a large number of independent computing devices is not new. For decades, the realm of high-performance computing has tackled this problem. The challenges faced by people writing software for supercomputers many years ago possess now trickled down to desktop and even mobile computing platforms.

    In the PC industry, some people saw this coming earlier than others. Almost 20 years ago, exist Inc. was formed around the concept of creating a PC platform unconstrained by legacy limitations and entirely prepared for the coming abundance of independent computing units on the desktop. To that end, exist created the BeBox, a dual-CPU desktop computer, and BeOS, a brand-new operating system.

    The signature enmesh phrase for BeOS was "pervasive multithreading." The BeBox and other machines running BeOS leveraged every ounce of the diminutive (by today's standards, anyway) computing resources at their disposal. The demos were impressive. A dual 66 MHz machine (don't accomplish me define another graph) could play multiple videos simultaneously while also playing several audio tracks from a CD—some backwards— and complete the while, the user interface remained completely responsive.

    Let me divulge you, having lived through this age myself, the experience was mind-blowing at the time. BeOS created instant converts out of hundreds of technology enthusiasts, many of whom maintain that today's desktop computing experience soundless doesn't match the responsiveness of BeOS. This is certainly exact emotionally, if not necessarily literally.

    After nearly purchasing exist in the late 1990s, Apple bought NeXT instead, and the repose is history. But had Apple gone with goal exist instead, Mac developers might possess had a jagged road ahead. While complete that pervasive multithreading made for impressive technology demos and a much user experience, it could exist extremely demanding on the programmer. BeOS was complete about threads, going so far as to maintain a divorce thread for each window. Whether you liked it or not, your BeOS program was going to exist multithreaded.

    Parallel programming is notoriously hard, with the manual management of POSIX-style threads representing the deep terminate of that pool. The best programmers in the world are hard-pressed to create large multithreaded programs in low-level languages like C or C++ without finding themselves impaled on the spikes of deadlock, race conditions, and other perils inherent in the expend of in multiple simultaneous threads of execution that participate the selfsame reminiscence space. Extremely heedful application of locking primitives is required to avoid performance-robbing levels of contention for shared data—and the bugs, oh the bugs! The term "Heisenbug" may as well possess been invented for multithreaded programming.

    Nineteen years after exist tilted at the windmill of the widening swath of silicon in desktop PCs, the challenge has only grown. Those transistors are out there, man—more than ever before. Single-threaded programs on today's high-end desktop Macs, even when using "100%" CPU, extend but a lone glowing tower in a sea of sixteen otherwise empty lanes on a CPU monitor window.

    A wide-open  unostentatious of transistorsA wide-open unostentatious of transistors

    And woe exist unto the user if that pegged CPU core is running the main thread of a GUI application on Mac OS X. A CPU-saturated main thread means no novel user inputs are being pulled off the event queue by the application. A few seconds of that and an aged friend makes its appearance: the spinning beach ball of death.


    Nooooooooo!!! Image from The Iconfactory

    This is the enemy: hardware with more computing resources than programmers know what to achieve with, most of it completely idle, and complete the while the user is utterly blocked in his attempts to expend the current application. What's Snow Leopard's answer? Read on…

    Grand Central Dispatch Apple's GCD branding: <a href="http://en.wikipedia.org/wiki/Foamer">Railfan</a> <a href="http://en.wikipedia.org/wiki/Fan_service">service</a>Apple's GCD branding: Railfan service

    Snow Leopard's retort to the concurrency conundrum is called imposing Central Dispatch (GCD). As with QuickTime X, the cognomen is extremely apt, though this is not entirely lucid until you understand the technology.

    The first thing to know about GCD is that it's not a novel Cocoa framework or similar special-purpose frill off to the side. It's a unostentatious C library baked into the lowest levels of Mac OS X. (It's in libSystem, which incorporates libc and the other code that sits at the very bottom of userspace.)

    There's no need to link in a novel library to expend GCD in your program. Just #include <dispatch/dispatch.h> and you're off to the races. The fact that GCD is a C library means that it can exist used from complete of the C-derived languages supported on Mac OS X: Objective-C, C++, and Objective-C++.

    Queues and threads

    GCD is built on a few simple entities. Let's start with queues. A queue in GCD is just what it sounds like. Tasks are enqueued, and then dequeued in FIFO order. (That's "First In, First Out," just like the checkout line at the supermarket, for those who don't know and don't want to result the link.) Dequeuing the chore means handing it off to a thread where it will execute and achieve its actual work.

    Though GCD queues will hand tasks off to threads in FIFO order, several tasks from the selfsame queue may exist running in parallel at any given time. This animation demonstrates.

    A imposing Central Dispatch queue in action

    You'll notice that chore B completed before chore A. Though dequeuing is FIFO, chore completion is not. also note that even though there were three tasks enqueued, only two threads were used. This is an necessary feature of GCD which we'll argue shortly.

    But first, let's peek at the other kindly of queue. A serial queue works just like a household queue, except that it only executes one chore at a time. That means chore completion in a serial queue is also FIFO. Serial queues can exist created explicitly, just like household queues, but each application also has an implicit "main queue" which is a serial queue that runs on the main thread.

    The animation above shows threads appearing as labor needs to exist done, and disappearing as they're no longer needed. Where achieve these threads approach from and where achieve they proceed when they're done? GCD maintains a global pool of threads which it hands out to queues as they're needed. When a queue has no more pending tasks to accelerate on a thread, the thread goes back into the pool.

    This is an extremely necessary aspect of GCD's design. Perhaps surprisingly, one of the most difficult parts of extracting maximum performance using traditional, manually managed threads is figuring out exactly how many threads to create. Too few, and you risk leaving hardware idle. Too many, and you start to disburse a significant amount of time simply shuffling threads in and out of the available processor cores.

    Let's philosophize a program has a problem that can exist split into eight separate, independent units of work. If this program then creates four threads on an eight-core machine, is this an sample of creating too many or too few threads? Trick question! The retort is that it depends on what else is happening on the system.

    If six of the eight cores are totally saturated doing some other work, then creating four threads will just require the OS to blow time rotating those four threads through the two available cores. But wait, what if the process that was saturating those six cores finishes? Now there are eight available cores but only four threads, leaving half the cores idle.

    With the exception of programs that can reasonably anticipate to possess the entire machine to themselves when they run, there's no passage for a programmer to know ahead of time exactly how many threads he should create. Of the available cores on a particular machine, how many are in use? If more become available, how will my program know?

    The bottom line is that the optimal number of threads to set in flight at any given time is best determined by a single, globally aware entity. In Snow Leopard, that entity is GCD. It will retain zero threads in its pool if there are no queues that possess tasks to run. As tasks are dequeued, GCD will create and dole out threads in a passage that optimizes the expend of the available hardware. GCD knows how many cores the system has, and it knows how many threads are currently executing tasks. When a queue no longer needs a thread, it's returned to the pool where GCD can hand it out to another queue that has a chore ready to exist dequeued.

    There are further optimizations inherent in this scheme. In Mac OS X, threads are relatively heavyweight. Each thread maintains its own set of register values, stack pointer, and program counter, plus kernel data structures tracking its security credentials, scheduling priority, set of pending signals and signal masks, etc. It complete adds up to over 512 KB of overhead per thread. Create a thousand threads and you've just burned about a half a gigabyte of reminiscence and kernel resources on overhead alone, before even considering the actual data within each thread.

    Compare a thread's 512 KB of baggage with GCD queues which possess a mere 256 bytes of overhead. Queues are very lightweight, and developers are encouraged to create as many of them as they need—thousands, even. In the earlier animation, when the queue was given two threads to process its three tasks, it executed two tasks on one of the threads. Not only are threads heavyweight in terms of reminiscence overhead, they're also relatively costly to create. Creating a novel thread for each chore would exist the worst feasible scenario. Every time GCD can expend a thread to execute more than one task, it's a win for overall system efficiency.

    Remember the problem of the programmer trying to motif out how many threads to create? Using GCD, he doesn't possess to worry about that at all. Instead, he can concentrate entirely on the optimal concurrency of his algorithm in the abstract. If the best-case scenario for his problem would expend 500 concurrent tasks, then he can proceed ahead and create 500 GCD queues and ration his labor among them. GCD will motif out how many actual threads to create to achieve the work. Furthermore it will adjust the number of threads dynamically as the conditions on the system change.

    But perhaps most importantly, as novel hardware is released with more and more CPU cores, the programmer does not need to change his application at all. Thanks to GCD, it will transparently Take advantage of any and complete available computing resources, up to—but not past!—the optimal amount of concurrency as originally defined by the programmer when he chose how many queues to create.

    But wait, there's more! GCD queues can actually exist arranged in arbitrarily complex directed acyclic graphs. (Actually, they can exist cyclic too, but then the behavior is undefined. Don't achieve that.) Queue hierarchies can exist used to funnel tasks from disparate subsystems into a narrower set of centrally controlled queues, or to constrain a set of household queues to delegate to a serial queue, effectively serializing them complete indirectly.

    There are also several levels of priority for queues, dictating how often and with what urgency threads are distributed to them from the pool. Queues can exist suspended, resumed, and cancelled. Queues can also exist grouped, allowing complete tasks distributed to the group to exist tracked and accounted for as a unit.

    Overall, GCD's expend of queues and threads forms a simple, elegant, but also extremely pragmatic architecture.


    Okay, so GCD is a much passage to accomplish efficient expend of the available hardware. But is it really any better than BeOS's approach to multithreading? We've already seen a few ways that GCD avoids the pitfalls of BeOS (e.g., the reuse of threads and the maintenance of a global pool of threads that's correctly sized for the available hardware). But what about the problem of overwhelming the programmer by requiring threads in places where they complicate, rather than enhance the application?

    GCD embodies a philosophy that is at the opposite terminate of the spectrum from BeOS's "pervasive multithreading" design. Rather than achieving responsiveness by getting every feasible component of an application running concurrently on its own thread (and paying a ponderous price in terms of complex data sharing and locking concerns), GCD encourages a much more limited, hierarchical approach: a main application thread where complete the user events are processed and the interface is updated, and worker threads doing specific jobs as needed.

    In other words, GCD doesn't require developers to reflect about how best to split the labor of their application into multiple concurrent threads (though when they're ready to achieve that, GCD will exist willing and able to help). At its most basic level, GCD aims to embolden developers to run from thinking synchronously to thinking asynchronous. Something like this: "Write your application as usual, but if there's any section of its operation that can reasonably exist expected to Take more than a few seconds to complete, then for the value of Zarzycki, acquire it off the main thread!"

    That's it; no more, no less. Beach ball banishment is the cornerstone of user interface responsiveness. In some respects, everything else is gravy. But most developers know this intuitively, so why achieve they soundless see the beach ball in Mac OS X applications? Why don't complete applications already execute complete of their potentially long-running tasks on background threads?

    A few reasons possess been mentioned already (e.g., the hardship of knowing how many threads to create) but the titanic one is much more pragmatic. Spinning off a thread and collecting its result has always been a bit of a pain. It's not so much that it's technically difficult, it's just that it's such an categorical fracture from coding the actual labor of your application to coding complete this task-management plumbing. And so, especially in borderline cases, like an operation that may Take 3 to 5 seconds, developers just achieve it synchronously and run onto the next thing.

    Unfortunately, there's a surprising number of very common things that an application can achieve that execute quickly most of the time, but possess the potential to Take much longer than a few seconds when something goes wrong. Anything that touches the file system may stall at the lowest levels of the OS (e.g., within blocking read() and write() calls) and exist theme to a very long (or at least an "unexamined-by-the-application-developer") timeout. The selfsame goes for cognomen lookups (e.g., DNS or LDAP), which almost always execute instantly, but enmesh many applications completely off-guard when they start taking their sweet time to recur a result. Thus, even the most meticulously constructed Mac OS X applications can terminate up throwing the beach ball in their face from time to time.

    With GCD, Apple is epigram it doesn't possess to exist this way. For example, suppose a document-based application has a button that, when clicked, will dissect the current document and pomp some gripping statistics about it. In the common case, this analysis should execute in under a second, so the following code is used to connect the button with an action:

    - (IBAction)analyzeDocument:(NSButton *)sender { NSDictionary *stats = [myDoc analyze]; [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }

    The first line of the role body analyzes the document, the second line updates the application's internal state, and the third line tells the application that the statistics view needs to exist updated to reflect this novel state. It complete follows a very common pattern, and it works much as long as None of these steps—which are complete running on the main thread, remember—takes too long. Because after the user presses the button, the main thread of the application needs to wield that user input as rapidly as feasible so it can acquire back to the main event loop to process the next user action.

    The code above works much until a user opens a very large or very complex document. Suddenly, the "analyze" step doesn't Take one or two seconds, but 15 or 30 seconds instead. Hello, beach ball. And still, the developer is likely to hem and haw: "This is really an exceptional situation. Most of my users will never open such a large file. And anyway, I really don't want to start reading documentation about threads and adding complete that extra code to this simple, four-line function. The plumbing would dwarf the code that does the actual work!"

    Well, what if I told you that you could run the document analysis to the background by adding just two lines of code (okay, and two lines of closing braces), complete located within the existing function? No application-global objects, no thread management, no callbacks, no dispute marshalling, no context objects, not even any additional variables. Behold, imposing Central Dispatch:

    - (IBAction)analyzeDocument:(NSButton *)sender { dispatch_async(dispatch_get_global_queue(0, 0), ^{ NSDictionary *stats = [myDoc analyze]; dispatch_async(dispatch_get_main_queue(), ^{ [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }); }); }

    There's a hell of a lot of packed into those two lines of code. complete of the functions in GCD start with dispatch_, and you can see four such calls in the blue lines of code above. The key to the minimal invasiveness of this code is revealed in the second dispute to the two dispatch_async() calls. Thus far, I've been discussing "units of work" without specifying how, exactly, GCD models such a thing. The answer, now revealed, should seem obvious in retrospect: blocks! The skill of blocks to capture the surrounding context is what allows these GCD calls to exist dropped perquisite into some existing code without requiring any additional setup or re-factoring or other contortions in service of the API.

    But the best section of this code is how it deals with the problem of detecting when the background chore completes and then showing the result. In the synchronous code, the dissect routine convoke and the code to update the application pomp simply materialize in the desired sequence within the function. In the asynchronous code, miraculously, this is soundless the case. Here's how it works.

    The outer dispatch_async() convoke puts a chore on a global concurrent GCD queue. That task, represented by the block passed as the second argument, contains the potentially time-consuming dissect routine call, plus another convoke to dispatch_async() that puts a chore onto the main queue—a serial queue that runs on the main thread, remember—to update the application's user interface.

    User interface updates must complete exist done from the main thread in a Cocoa application, so the code in the inner block could not exist executed anywhere else. But rather than having the background thread send some kindly of special-purpose notification back to the main thread when the dissect routine convoke completes (and then adding some code to the application to detect and wield this notification), the labor that needs to exist done on the main thread to update the pomp is encapsulated in yet another block within the larger one. When the dissect convoke is done, the inner block is set onto the main queue where it will (eventually) accelerate on the main thread and achieve its labor of updating the display.

    Simple, elegant, and effective. And for developers, no more excuses.

    Believe it or not, it's just as simple to Take a serial implementation of a string of independent operations and parallelize it. The code below does labor on import elements of data, one after the other, and then summarizes the results once complete the elements possess been processed.

    for (i = 0; i < count; i++) { results[i] = do_work(data, i); } total = summarize(results, count);

    Now here's the parallel version which puts a divorce chore for each constituent onto a global concurrent queue. (Again, it's up to GCD to resolve how many threads to actually expend to execute the tasks.)

    dispatch_apply(count, dispatch_get_global_queue(0, 0), ^(size_t i) { results[i] = do_work(data, i); }); total = summarize(results, count);

    And there you possess it: a for loop replaced with a concurrency-enabled equivalent with one line of code. No preparation, no additional variables, no impossible decisions about the optimal number of threads, no extra labor required to wait for complete the independent tests to complete. (The dispatch_apply() convoke will not recur until complete the tasks it has dispatched possess completed.) Stunning.

    Grand Central Awesome

    Of complete the APIs added in Snow Leopard, imposing Central Dispatch has the most far-reaching implications for the future of Mac OS X. Never before has it been so simple to achieve labor asynchronously and to spread workloads across many CPUs.

    When I first heard about imposing Central Dispatch, I was extremely skeptical. The greatest minds in computer science possess been working for decades on the problem of how best to extract parallelism from computing workloads. Now here was Apple apparently promising to decipher this problem. Ridiculous.

    But imposing Central Dispatch doesn't actually address this issue at all. It offers no abet whatsoever in deciding how to split your labor up into independently executable tasks—that is, deciding what pieces can or should exist executed asynchronously or in parallel. That's soundless entirely up to the developer (and soundless a tough problem). What GCD does instead is much more pragmatic. Once a developer has identified something that can exist split off into a divorce task, GCD makes it as simple and non-invasive as feasible to actually achieve so.

    The expend of FIFO queues, and especially the being of serialized queues, seems counter to the spirit of ubiquitous concurrency. But we've seen where the Platonic ideal of multithreading leads, and it's not a pleasant position for developers.

    One of Apple's slogans for imposing Central Dispatch is "islands of serialization in a sea of concurrency." That does a much job of capturing the practical reality of adding more concurrency to run-of-the-mill desktop applications. Those islands are what sequester developers from the thorny problems of simultaneous data access, deadlock, and other pitfalls of multithreading. Developers are encouraged to identify functions of their applications that would exist better executed off the main thread, even if they're made up of several sequential or otherwise partially interdependent tasks. GCD makes it simple to fracture off the entire unit of labor while maintaining the existing order and dependencies between subtasks.

    Those with some multithreaded programming experience may exist unimpressed with the GCD. So Apple made a thread pool. titanic deal. They've been around forever. But the angels are in the details. Yes, the implementation of queues and threads has an elegant simplicity, and baking it into the lowest levels of the OS really helps to lower the perceived barrier to entry, but it's the API built around blocks that makes imposing Central Dispatch so attractive to developers. Just as Time Machine was "the first backup system people will actually use," imposing Central Dispatch is poised to finally spread the heretofore gloomy craft of asynchronous application design to complete Mac OS X developers. I can't wait.

    OpenCL Somehow, OpenCL got in on the <a href="http://arstechnica.com/apple/2007/10/mac-os-x-10-5/8/#core-spheres">"core" branding</a>Somehow, OpenCL got in on the "core" branding

    So far, we've seen a few examples of doing more with more: a new, more modern compiler infrastructure that supports an necessary novel language feature, and a powerful, pragmatic concurrency API built on top of the novel compilers' back for said language feature. complete this goes a long passage towards helping developers and the OS itself accomplish maximum expend of the available hardware.

    But CPUs are not the only components experiencing a glut of transistors. When it comes to the proliferation of independent computation engines, another piece of silicon inside every Mac is the undisputed title holder: the GPU.

    The numbers divulge the tale. While Mac CPUs contain up to four cores (which may define up as eight logical cores thanks to symmetric multithreading), high-end GPUs contain well over 200 processor cores. While CPUs are just now edging over 100 GFLOPS, the best GPUs are capable of over 1,000 GFLOPS. That's one trillion floating-point operations per second. And like CPUs, GPUs now approach more than one on a board.

    Writing for the GPU

    Unfortunately, the cores on a GPU are not general-purpose processors (at least not yet). They're much simpler computing engines that possess evolved from the fixed-function silicon of their ancestors that could not exist programmed directly at all. They don't back the affluent set of instructions available on CPUs, the maximum size of the programs that will accelerate is often limited and very small, and not complete of the features of the industry-standard IEEE floating-point computation specification are supported.

    Today's GPUs can exist programmed, but the most common forms of programmability are soundless firmly planted in the world of graphics programming: vertex shaders, geometry shaders, pixel shaders. Most of the languages used to program GPUs are similarly graphically focused: HLSL, GLSL, Cg.

    Nevertheless, there are computational tasks outside the realm of graphics that are a top-notch appropriate for GPU hardware. It would exist nice if there were a non-graphics-oriented language to write them in. Creating such a thing is quite a challenge, however. GPU hardware varies wildly in every imaginable way: number and sort of execution units, available data formats, instruction sets, reminiscence architecture, you cognomen it. Programmers don't want to exist exposed to these differences, but it's difficult to labor around the complete lack of a feature or the unavailability of a particular data type.

    GPU vendor NVIDIA gave it a shot, however, and produced CUDA: a subset of the C language with extensions for vector data types, data storage specifiers that reflect typical GPU reminiscence hierarchy, and several bundled computational libraries. CUDA is but one entrant in the burgeoning GPGPU realm (General-Purpose computing on Graphics Processing Units). But coming from a GPU vendor, it faces an uphill battle with developers who really want a vendor-agnostic solution.

    In the world of 3D programming, OpenGL fills that role. As you've surely guessed by now, OpenCL aims to achieve the selfsame for general-purpose computation. In fact, OpenCL is supported by the selfsame consortium as OpenGL: the ominously named Khronos Group. But accomplish no mistake, OpenCL is Apple's baby.

    Apple understood that OpenCL's best haphazard of success was to become an industry standard, not just an Apple technology. To accomplish that happen, Apple needed the cooperation of the top GPU vendors, plus an agreement with an established, widely-recognized standards body. It took a while, but now it's complete approach together.

    OpenCL is a lot like CUDA. It uses a C-like language with the vector extensions, it has a similar model of reminiscence hierarchy, and so on. This is no surprise, considering how closely Apple worked with NVIDIA during the development of OpenCL. There's also no passage any of the titanic GPU vendors would radically alter their hardware to back an as-yet-unproven standard, so OpenCL had to labor well with GPUs already designed to back CUDA, GLSL, and other existing GPU programming languages.

    The OpenCL difference

    This is complete well and good, but to possess any repercussion on the day-to-day life of Mac users, developers actually possess to expend OpenCL in their applications. Historically, GPGPU programming languages possess not seen much expend in traditional desktop applications. There are several reasons for this.

    Early on, writing programs for the GPU often required the expend of vendor-specific assembly languages that were far removed from the experience of writing a typical desktop application using a contemporary GUI API. The more C-like languages that came later remained either graphics-focused, vendor-specific, or both. Unless running code on the GPU would accelerate a core component of an application by an order of magnitude, most developers soundless could not exist bothered to navigate this curious world.

    And even if the GPU did give a huge accelerate boost, relying on graphics hardware for general-purpose computation was very likely to narrow the potential audience for an application. Many older GPUs, especially those establish in laptops, cannot accelerate languages like CUDA at all.

    Apple's key decision in the design of OpenCL was to allow OpenCL programs to accelerate not just on GPUs, but on CPUs as well. An OpenCL program can query the hardware it's running on and enumerate complete eligible OpenCL devices, categorized as CPUs, GPUs, or dedicated OpenCL accelerators (the IBM Cell Blade server—yes, that Cell—is apparently one such device). The program can then dispatch its OpenCL tasks to any available device. It's also feasible to create a lone logical device consisting of any combination of eligible computing resources: two GPUs, a GPU and two CPUs, etc.

    The advantages of being able to accelerate OpenCL programs on both CPUs and GPUs are obvious. Every Mac running Snow Leopard, not just those with the recent-model GPUs, can accelerate a program that contains OpenCL code. But there's more to it than that.

    Certain kinds of algorithms actually accelerate faster on high-end multi-core CPUs than on even the very fastest available GPUs. At WWDC 2009, an engineer from Electronic Arts demonstrated an OpenCL port of a skinning engine from one of its games running over four times faster on a four-core Mac Pro than on an NVIDIA GeForce GTX285. Restructuring the algorithm and making many other changes to better suit the limitations (and strengths) of the GPU pushed it back ahead of the CPU by a wide margin, but sometimes you just want the system you possess to accelerate well as-is. Being able to target the CPU is extremely useful in those cases.

    Moreover, writing vector code for Intel CPUs "the old-fashioned way" can exist a real pain. There's MMX, SSE, SSE2, SSE3, and SSE4 to deal with, complete with slightly different capabilities, and complete of which constrain the programmer to write code like this:

    r1 = _mm_mul_ps(m1, _mm_add_ps(x1, x2));

    OpenCL's aboriginal back for vector types de-clutters the code considerably:

    r1 = m1 * (x1 + x2);

    Similarly, OpenCL's back for implicit parallelism makes it much easier to Take advantage of multiple CPU cores. Rather than writing complete the logic to split your data into pieces and ration those pieces to the parallel-computing hardware, OpenCL lets you write just the code to operate on a lone piece of the data and then send it, along with the entire block of data and the desired flush of parallelism, to the computing device.

    This arrangement is taken for granted in traditional graphics programming, where code implicitly works on complete pixels in a texture or complete vertices in a polygon; the programmer only needs to write code that will exist in the "inner loop," so to speak. An API with back for this kindly of parallelism that runs on CPUs as well as GPUs fills an necessary gap.

    Writing to OpenCL also future-proofs task- or data-parallel code. Just as the selfsame OpenGL code will acquire faster and faster as newer, more powerful GPUs are released, so too will OpenCL code perform better as CPUs and GPUs acquire faster. The extra layer of abstraction that OpenCL provides makes this possible. For example, though vector code written several years ago using MMX got faster as CPU clock speeds increased, a more significant performance boost likely requires porting the code to one of the newer SSE instruction sets.

    As newer, more powerful vector instruction sets and parallel hardware becomes available, Apple will update its OpenCL implementations to Take advantage of them, just as video card makers and OS vendors update their OpenGL drivers to Take advantage of faster GPUs. Meanwhile, the application developer's code remains unchanged. Not even a recompile is required.

    Here exist dragons (and trains)

    How, you may wonder, can the selfsame compiled code terminate up executing using SSE2 on one machine and SSE4 on another, or on an NVIDIA GPU on one machine and an ATI GPU on another? To achieve so would require translating the device-independent OpenCL code to the instruction set of the target computing device at runtime. When running on a GPU, OpenCL must also ship the data and the newly translated code over to the video card and collect the results at the end. When running on the CPU, OpenCL must organize for the requested flush of parallelism by creating and distributing threads appropriately to the available cores.

    Well, wouldn't you know it? Apple just happens to possess two technologies that decipher these exact problems.

    Want to compile code "just in time" and ship it off to a computing device? That's what LLVM was born to do—and, indeed, what Apple did with it in Leopard, albeit on a more limited scale. OpenCL is a natural extension of that work. LLVM allows Apple to write a lone code generator for each target instruction set, and concentrate complete of its effort on a lone device-independent code optimizer. There's no longer any need to duplicate these tasks, using one compiler to create the static application executable and having to jury-rig another for just-in-time compilation.

    (Oh, and by the way, recollect Core Image? That's another API that needs to compile code just-in-time and ship it off to execute on parallel hardware like GPUs and multi-core CPUs. In Snow Leopard, Core Image has been re-implemented using OpenCL, producing a hefty 25% overall performance boost.)

    To wield chore parallelism and provision threads, OpenCL is built on top of imposing Central Dispatch. This is such a natural appropriate that it's a bit surprising that the OpenCL API doesn't expend blocks. I reflect Apple decided that it shouldn't press its luck when it comes to getting its home-grown technologies adopted by other vendors. This decision already seems to exist paying off, as AMD has its own OpenCL implementation under way.

    The top of the pyramid

    Though the underlying technologies, Clang, blocks and imposing Central Dispatch, will undoubtedly exist more widely used by developers, OpenCL represents the culmination of that particular technological thread in Snow Leopard. This is the gold gauge of software engineering: creating a novel public API by structure it on top of lower-level, but equally well-designed and implemented public APIs.

    A unified abstraction for the ever-growing heterogeneous collection of parallel computing silicon in desktop computers was sorely needed. We've got an increasing population of powerful CPU cores, but they soundless exist in numbers that are orders of magnitude lower than the hundreds of processing units in modern GPUs. On the other hand, GPUs soundless possess a ways to proceed to enmesh up with the power and flexibility of a full-fledged CPU core. But even with complete the differences, writing code exclusively for either one of those worlds soundless smacks of leaving money on the table.

    With OpenCL in hand, there's no longer a need to set complete your eggs in one silicon basket. And with the advent of hybrid CPU/GPU efforts like Intel's Larabee, which expend CPU-caliber processing engines, but in much higher numbers, OpenCL may prove even more necessary in the coming years.

    Transistor harvest

    Collectively, the concurrency-enabling features introduced in Snow Leopard delineate the biggest boost to asynchronous and parallel software development in any Mac OS X release—perhaps in any desktop operating system release ever. It may exist difficult for end-users to acquire excited about "plumbing" technologies like imposing Central Dispatch and OpenCL, let lonely compilers and programming language features, but it's upon these foundations that developers will create ever-more-impressive edifices of software. And if those applications tower over their synchronous, serial predecessors, it will exist because they stand on the shoulders of giants.

    QuickTime Player's  novel icon (Not a fan)QuickTime Player's novel icon (Not a fan) QuickTime Player

    There's been some confusion surrounding QuickTime in Snow Leopard. The earlier section about QuickTime X explains what you need to know about the present and future of QuickTime as a technology and an API. But a few of Apple's decisions—and the extremely overloaded signification of the word "QuickTime" in the minds of consumers—have blurred the picture somewhat.

    The first head-scratcher occurs during installation. If you betide to click on the "Customize…" button during installation, you'll see the following options:

    QuickTime 7 is an optional install?QuickTime 7 is an optional install?

    We've already talked about Rosetta being an optional install, but QuickTime 7 too? Isn't QuickTime severely crippled without QuickTime 7? Why in the world would that exist an optional install?

    Well, there's no need to panic. That detail in the installer should actually read "QuickTime Player 7." QuickTime 7, the aged but extremely capable media framework discussed earlier, is installed by default in Snow Leopard—in fact, it's mandatory. But the player application, the one with the aged blue "Q" icon, the one that many casual users actually reflect of as being "QuickTime," that's been replaced with a novel QuickTime-X-savvy version sporting a pudgy novel icon (see above right).

    The novel player application is a titanic departure from the old. Obviously, it leverages QuickTime X for more efficient video playback, but the user interface is also completely new. Gone are the gray edge and bottom-mounted playback controls from the aged QuickTime Player, replaced by a frameless window with a black title bar and a floating, moveable set of controls.

    The  novel QuickTime Player: boldly going where <a href="http://code.google.com/p/niceplayer/">NicePlayer</a> has gone before Enlarge / The novel QuickTime Player: boldly going where NicePlayer has gone before

    It's like a combination of the window treatment of the excellent NicePlayer application and the full-screen playback controls from the aged QuickTime Player. I'm a bit bothered by two things. First, the ever-so-slightly clipped corners seem like a wrong idea. Am I just hypothetical to give up those dozen-or-so pixels? NicePlayer does it right, showing crisp, square corners.

    Second, the floating playback controls obscure the movie. What if I'm scrubbing around looking for something in that section of the frame? Yes, you can run the controls, but what if I'm looking for something in an unknown location in the frame? Also, the title bar obscures an entire swath of the top of the frame, and this can't exist moved. I value the compactness of this approach, but it'd exist nice if the title bar overlap could exist disabled and the controls could exist dragged off the movie entirely and docked to the bottom or something.

    (One blessing for people who participate my OCD tendencies: if you run the floating controls, they don't recollect their position the next time you open a movie. Why is that a blessing? Because if it worked the other way, we'd complete disburse passage too much time fretting about their inability to restore the controller to its default, precisely centered position. Sad, but true.)

    The novel QuickTime Player presents a decidedly iMovie-like (or is it iPhone-like, nowadays?) interface for trimming video. Still-frame thumbnails are placed side-by-side to profile a timeline, with adjustable stops at each terminate for trimming.

    Trimming in the  novel QuickTime Player Enlarge / Trimming in the novel QuickTime Player

    Holding down the option key changes from a thumbnail timeline to an audio waveform display:

    Trimming with audio waveform view Enlarge / Trimming with audio waveform view

    In both the video and audio cases, I possess to prodigy exactly how useful the fancy timeline appearances are. The audio waveform is quite tiny and compressed, and the limited horizontal space of the in-window pomp means a movie can only define a handful of video frames in its timeline. Also, if there's any skill to achieve fine adjustments using something other than extremely heedful mouse movements (which are necessarily theme to a limited resolution) then I couldn't find it. Final nick Pro this is not.

    QuickTime Player has scholarly another novel trick: screen recording. The controls are limited, so more demanding users will soundless possess a need for a full-featured screen recorder, but QuickTime Player gets the job done.

    Screen recording in QuickTime PlayerScreen recording in QuickTime Player

    There's also an audio-only option, with a similarly simplified collection of settings.

    Audio recordingAudio recording

    Finally, the novel QuickTime Player has the skill to upload a movie directly to YouTube and MobileMe, send one via e-mail, or add it to your iTunes library. The export options are also vastly simplified, with preset options for iPhone/iPod, Apple TV, and HD 480p and 720p.

    Unfortunately, the list of things you can't achieve with the novel QuickTime Player is quite long. You can't cut, copy, and paste whimsical portions of a movie (trimming only affects the ends); you can't extract or delete individual tracks or overlay one track onto another (optionally scaling to fit); you can't export a movie by choosing from the complete set of available QuickTime audio and video codecs. complete of these things were feasible with the aged QuickTime Player—if, that is, you paid the $30 for a QuickTime Pro license. In the past, I've described this extra fee as "criminally stupid", but the features it enabled in QuickTime Player were really useful.

    It's tempting to ascribe their absence in the novel QuickTime Player to the previously discussed limitations of QuickTime X. But the novel QuickTime Player is built on top of QTKit, which serves as a front-end for both QuickTime X and QuickTime 7. And it does, after all, feature some limited editing features like trimming, plus some previously "Pro"-only features like full-screen playback. Also, the novel QuickTime Player can indeed play movies using third-party plug-ins—a feature clearly powered by QuickTime 7.

    Well, Snow Leopard has an extremely pleasant flabbergast waiting for you if you install the optional QuickTime Player 7. When I did so, what I got was the aged QuickTime Player—somewhat insultingly installed in the "Utilities" folder—with complete of its "Pro" features permanently unlocked. Yes, the tyranny of QuickTime Pro seems to exist at an end…

    QuickTime Pro: now free for everyone?QuickTime Pro: now free for everyone?

    …but perhaps the key word above is "seems," because QuickTime Player 7 does not possess complete "pro" features unlocked for everyone. I installed Snow Leopard onto an empty disk, and QuickTime 7 was not automatically installed (as it is when the installer detects an existing QuickTime Pro license on the target disk). After booting from my fresh Snow Leopard volume, I manually installed the "QuickTime 7" optional component using the Snow Leopard installer disk.

    The result for me was a QuickTime Player 7 application with complete pro features unlocked and with no visible QuickTime Pro registration information. I did, however, possess a QuickTime Pro license on one of the attached drives. Apparently, the installer detected this and gave me an unlocked QuickTime Player 7 application, even though the boot volume never had a QuickTime Pro license on it.

    The Dock

    The novel appearance of some aspects of the Dock are accompanied by some novel functionality as well. Clicking and holding on a running application's Dock icon now triggers Expos�, but only for the windows belonging to that application. Dragging a file onto a docked application icon and holding it there for a bit produces the selfsame result. You can then continue that selfsame drag onto one of the Exposé window thumbnails and hover there a bit to bring that window to the front and drop the file into it. It's a pretty handy technique, once you acquire in the use of doing it.

    The Exposé pomp itself is also changed. Now, minimized windows are displayed in smaller profile on the bottom of the screen below a thin line.

    Dock Exposé with  novel placement of minimized windows Enlarge / Dock Exposé with novel placement of minimized windows

    In the screenshot above, you'll notice that None of the minimized windows materialize in my Dock. That's thanks to another welcome addition: the skill to minimize windows "into" the application icon. You'll find the setting for this in the Dock's preference pane.

    New Dock preference: Minimize windows into application iconNew Dock preference: Minimize windows into application icon Minimized windows in a Dock application menuMinimized window denoted by a diamond

    Once set, minimized windows will slip behind the icon of their parent application and then disappear. To acquire them back, either right-click the application icon (see right) or trigger Exposé.

    The Dock's grid view for folders now incorporates a scroll bar when there are too many items to appropriate comfortably. Clicking on a folder icon in the grid now shows that folder's contents within the grid, allowing you to navigate down several folders to find a buried item. A tiny "back" navigation button appears once you descend.

    These are complete useful novel behaviors, and quite a gratuity considering the hypothetical "no novel features" stance of Snow Leopard. But the fundamental nature of the Dock remains the same. Users who want a more resilient or more powerful application launcher/folder organizer/window minimization system must soundless either sacrifice some functionality (e.g., Dock icon badges and bounce notifications) or continue to expend the Dock in addition to a third-party application.

    The option to retain minimized windows from cluttering up the Dock was long overdue. But my enthusiasm is tempered by my frustration at the continued inability to click on a docked folder and possess it open in the Finder, while also retaining the skill to drag items into that folder. This was the default behavior for docked folders for the first six years of Mac OS X's life, but it changed in Leopard. Snow Leopard does not better matters.

    Docking an alias to a folder provides the single-click-open behavior, but items cannot exist dragged into a docked folder alias for some inexplicable reason. (Radar 5775786, closed in March 2008 with the terse explanation, "not currently supported.") Worse, dragging an detail to a docked folder alias looks like it will labor (the icon highlights) but upon release, the dragged detail simply springs back to its original location. I really hoped this one would acquire fixed in Snow Leopard. No such luck.

    Dock grid view's in-place navigation with back buttonDock grid view's in-place navigation with back button The Finder

    One of the earliest leaked screenshots of Snow Leopard included an innocuous-looking "Get Info…" window for the Finder, presumably to define that its version number had been updated to 10.6. The more gripping tidbit of information it revealed was that the Finder in Snow Leopard was a 64-bit application.

    The Mac OS X Finder started its life as the designated "dog food" application for the Carbon backward-compatibility API for Mac OS X. Over the years, the Finder has been a frequent target of dissatisfaction and scorn. Those wrong feelings frequently spilled over into the parallel debate over API supremacy: Carbon vs. Cocoa.

    "The Finder sucks because it's a Carbon app. What they need is a Cocoa Finder! Surely that will decipher complete their woes." Well, Snow Leopard features a 64-bit Finder, and as they complete know, Carbon was not ported to 64-bit. Et voila! A Cocoa Finder in Snow Leopard. (More on the woes in a bit.)

    The conversion to Cocoa followed the Snow Leopard formula: no novel features… except for maybe one or two. And so, the "new" Cocoa Finder looks and works almost exactly like the aged Carbon Finder. The biggest indicator of its "Cocoa-ness" is the extensive expend of Core Animation transitions. For example, when a Finder window does its schizophrenic transformation from a sidebar-bedecked browser window to its minimally-adorned form, it no longer happens in a blink. Instead, the sidebar slides away and fades, the toolbar shrinks, and everything tucks in to profile its novel shape.

    Despite crossing the line in a few cases, the Core Animation transitions achieve accomplish the application feel more polished, and yes, "more Cocoa." And presumably the expend of Cocoa made it so darn simple to add features that the developers just couldn't resist throwing in a few.

    The number-one feature request from ponderous column-view users has finally been implemented: sortable columns. The sort order applies to complete columns at once, which isn't as nice as per-column sorting, but it's much better than nothing at all. The sort order can exist set using a menu command (each of which has a keyboard shortcut) or by right-clicking in an unoccupied district of a column and selecting from the resulting context menu.

    Column view sorting context menu Enlarge / Column view sorting context menu Column view sorting menu Enlarge / Column view sorting menu

    Even the lowly icon view has been enhanced in Snow Leopard. Every icon-view window now includes a tiny slider to control the size of the icons.

    The Finder's icon view with its  novel slider controlThe Finder's icon view with its novel slider control

    This may seem a bit odd—how often achieve people change icon sizes?—but it makes much more sense in the context of previewing images in the Finder. This expend case is made even more material by the recent expansion of the maximum icon size to 512x512 pixels.

    The icon previews themselves possess been enhanced to better match the abilities available in Quick Look. set it complete together and you can smoothly zoom a tiny PDF icon, for example, into the impressively high-fidelity preview shown below, complete with the skill to turn pages. One press of the space bar and you'll progress to the even larger and more resilient Quick peek view. It's a pretty smooth experience.

    Not your father's icon: 512x512 pixels of multi-page PDF previewingNot your father's icon: 512x512 pixels of multi-page PDF previewing

    QuickTime previews possess been similarly enhanced. As you zoom in on the icon, it transforms into a miniature movie player, adorned with an odd circular progress indicator. Assuming users are willing to wrangle with the vagaries of the Finder's view settings successfully enough to acquire icon view to stick for the windows where it's most useful, I reflect that odd miniature slider is actually going to acquire a lot of use.

    The Finder's QuickTime preview. (The "glare" overlay is a bit much.)The Finder's QuickTime preview. (The "glare" overlay is a bit much.)

    List view also has a few enhancements—accidental, incidental, or otherwise. The drag district for each list view detail now spans the entire line. In Leopard, though the entire line was highlighted, only the file cognomen or icon portion could exist dragged. Trying to drag anywhere else just extended the selection to other items in the list view as the cursor was moved. I'm not positive whether this change in behavior is intentional or if it's just an unexamined consequence of the underlying control used for list view in the novel Cocoa Finder. Either way, thumbs up.

    Double-clicking on the dividing line between two column headers in list view will "right-size" that column. For most columns, this means expanding or shrinking to minimally appropriate the widest value in the column. Date headers will progressively shrink to define less verbose date formats. Supposedly, this worked intermittently in Leopard as well. But whether Cocoa is bringing this feature for the first time or is just making it labor correctly for the first time, it's a change for the better.

    Searching using the Finder's browser view is greatly improved by the implementation of one of those miniature things that many users possess been clamoring for year after year. There's now a preference to select the default scope of the search realm in the Finder window toolbar. Can I acquire an amen?

    Default Finder search location: configurable at last.Default Finder search location: configurable at last.

    Along similar lines, there are other long-desired enhancements that will proceed a long passage towards making the desktop environment feel more solid. A top-notch sample is the improved handling of the dreaded "cannot eject, disk in use" error. The obvious follow-up question from the user is, "Okay, so what's using it?" Snow Leopard finally provides that information.

    No more guessingNo more guessing

    (Yes, Mac OS X will reject to dismiss a disk if your current working directory in a command-line shell is on that disk. kindly of cool, but also kindly of annoying.)

    Another feasible user response to a disk-in-use mistake is, "I don't care. I'm in a hurry. Just dismiss it!" That's an option now as well.

    Forcible ejection in progressForcible ejection in progress

    Hm, but why did I acquire information about the offending application in one dialog, an option to constrain ejection in the other, but neither one presented both choices? It's a mystery to me, but presumably it's related to exactly what information the Finder has about the contention for the disk. (As always, the lsof command is available if you want to motif it out the old-fashioned way.)


    So does the novel Cocoa Finder finally exile complete of those embarrassing bugs from the bad-old days of Carbon? Not quite. This is essentially the "1.0" release of the Cocoa Finder, and it has its participate of 1.0 bugs. Here's one discovered by Glen Aspeslagh (see image right).

    Do you see it? If not, peek closer at the order of the dates in the supposedly sorted "Date Modified" column. So yeah, that aged Finder magic has not been entirely extinguished.

    There also remains some weirdness in the operation of the icon grid. In a view where grid snap is turned on (or is enabled transiently by holding down the command key during a drag) icons seem terrified of each other, leaving huge distances between themselves and their neighbors when they select which grid spot to snap to. It's as if the Finder lives in mortal terror that one of these files will someday acquire a 200-character filename that will overlap with a neighboring file's name.

    The worst incarnation of this behavior happens along the perquisite edge of the screen where mounted volumes materialize on the desktop. (Incidentally, this is not the default; if you want to see disks on your desktop, you must enable this preference in the Finder.) When I mount a novel disk, I'm often surprised to see where it ends up appearing. If there are any icons remotely nigh to the perquisite edge of the screen, the disk icon will reject to materialize there. Again, the Finder is not avoiding any actual cognomen or icon overlapping. It appears to exist avoiding the mere possibility of overlapping at some unspecified point in the future. Silly.

    Finder report card

    Overall, the Snow Leopard Finder takes several significant steps forward—64-bit/Cocoa future-proofing, a few new, useful features, added polish—and only a few shuffles backwards with the slight overuse of animation and the continued presence of some puzzling bugs. Considering how long it took the Carbon Finder to acquire to its pre-Snow-Leopard feature set and flush of polish, it's quite an achievement for a Cocoa Finder to match or exceed its predecessor in its very first release. I'm positive the Carbon vs. Cocoa warriors would possess had a realm day with that statement, were Carbon not set out to pasture in Leopard. But it was, and to the victor proceed the spoils.


    Snow Leopard's headline "one novel feature" is back for Microsoft Exchange. This appears to be, at least partially, yet another hand-me-down from the iPhone, which gained back for Exchange in its 2.0 release and expanded on it in 3.0. Snow Leopard's Exchange back is weaved throughout the expected crop of applications in Mac OS X: iCal, Mail, and Address Book.

    The titanic caveat is that it will only labor with a server running Exchange 2007 (Service Pack 1, Update Rollup 4) or later. While I'm positive Microsoft greatly appreciates any additional upgrade revenue this decision provides, it means that for users whose workplaces are soundless running older versions of Exchange, Snow Leopard's "Exchange support" might as well not exist.

    Those users are probably already running the only other viable Mac OS X Exchange client, Microsoft Entourage, so they'll likely just sit tight and wait for their IT departments to upgrade. Meanwhile, Microsoft is already making overtures to these users with the promised creation—finally—of an honest-to-goodness version of Outlook for Mac OS X.

    In my admittedly brief testing, Snow Leopard's Exchange back seems to labor as expected. I had to possess one of the Microsoft mavens in the Ars Orbiting HQ spin up an Exchange 2007 server just for the purposes of this review. However it was configured, complete I had to enter in the Mail application was my complete name, e-mail address, and password, and it automatically discovered complete material settings and configured iCal and Address engage for me.

    Exchange setup: surprisingly easyExchange setup: surprisingly easy

    Windows users are no doubt accustomed to this kindly of Exchange integration, but it's the first time I've seen it on the Mac platform—and that includes my many years of using Entourage.

    Access to Exchange-related features is decidedly subdued, in keeping with the existing interfaces for Mail, iCal, and Address Book. If you're expecting the swarm of panels and toolbar buttons establish in Outlook on Windows, you're in for a bit of a shock. For example, here's the "detail" view of a meeting in iCal.

    iCal event detailiCal event detail

    Clicking the "edit" button hardly reveals more.

    Event editor: that's it?Event editor: that's it?

    The "availability" window also includes the bare minimum number of controls and displays to acquire the job done.

    Meeting availability checker Enlarge / Meeting availability checker

    The integration into Mail and Address engage is even more subtle—almost entirely transparent. This is to exist construed as a feature, I suppose. But though I don't know enough about Exchange to exist completely sure, I can't quiver the emotion that there are Exchange features that remain inaccessible from Mac OS X clients. For example, how achieve I engage a "resource" in a meeting? If there's a passage to achieve so, I couldn't determine it.

    Still, even basic Exchange integration out-of-the-box goes long passage towards making Mac OS X more welcome in corporate environments. It remains to exist seen how convinced IT managers are of the "realness" of Snow Leopard's Exchange integration. But I've got to reflect that being able to send and receive mail, create and respond to meeting invitations, and expend the global corporate address engage is enough for any Mac user to acquire along reasonably well in an Exchange-centric environment.


    The thing is, there's not really much to philosophize about performance in Snow Leopard. Dozens of benchmark graphs lead to the selfsame simple conclusion: Snow Leopard is faster than Leopard. Not shockingly so, at least in the aggregate, but it's faster. And while isolating one particular subsystem with a micro-benchmark may divulge some impressive numbers, it's the passage these tiny changes combine to better the real-world experience of using the system that really makes a difference.

    One sample Apple gave at WWDC was making an initial Time Machine backup over the network to a Time Capsule. Apple's approach to optimizing this operation was to address each and every subsystem involved.

    Time Machine itself was given back for overlapping i/o. Spotlight indexing, which happens on Time Machine volumes as well, was identified as another time-consuming chore involved in backups, so its performance was improved. The networking code was enhanced to Take advantage of hardware-accelerated checksums where possible, and the software checksum code was hand-tuned for maximum performance. The performance of HFS+ journaling, which accompanies each file system metadata update, was also improved. For Time Machine backups that write to disk images rather than aboriginal HFS+ file systems, Apple added back for concurrent access to disk images. The amount of network traffic produced by AFP during backups has also been reduced.

    All of this adds up to a respectable 55% overall improvement in the accelerate of an initial Time Machine backup. And, of course, the performance improvements to the individual subsystems capitalize complete applications that expend them, not just Time Machine.

    This holistic approach to performance improvement is not likely to knock anyone's socks off, but every time you accelerate across a piece of functionality in Snow Leopard that disproportionately benefits from one of these optimized subsystems, it's a pleasure.

    For example, Snow Leopard shuts down and restarts much faster than Leopard. I'm not talking about boot time; I spell the time between the selection of the Shutdown or Restart command and when the system turns off or begins its novel boot cycle. Leopard doesn't Take long at complete to achieve this; only a few dozen of seconds when there are no applications open. But in Snow Leopard, it's so rapidly that I often thought the operating system had crashed rather than shut down cleanly. (That's actually not too far from the truth.)

    The performance boosts offered by earlier major releases of Mac OS X soundless dwarf Snow Leopard's speedup, but that's mostly because Mac OS X was so excruciatingly sluggish in its early years. It's simple to create a titanic performance delta when you're starting from something abysmally slow. The fact that Snow Leopard achieves consistent, measurable improvements over the already-speedy Leopard is complete the more impressive.

    And yes, for the seventh consecutive time, a novel release of Mac OS X is faster on the selfsame hardware than its predecessor. (And for the first time ever, it's smaller, too.) What more can you put a question to for, really? Even that aged performance bugaboo, window resizing, has been completely vanquished. Grab the corner of a fully-populated iCal window—the worst-case scenario for window resizing in the aged days—and quiver it as rapidly as you can. Your cursor will never exist more than a few millimeters from the window's grab handle; it tracks your frantic motion perfectly. On most Macs, this is actually exact in Leopard as well. It just goes to define how far Mac OS X has approach on the performance front. These days, they complete just Take it for granted, which is exactly the passage it should be.

    Grab bag

    In the "grab bag" section, I usually examine smaller, mostly unrelated features that don't warrant full-blown sections of their own. But when it comes to user-visible features, Snow Leopard is kindly of "all grab bag," if you know what I mean. Apple's even got its own incarnation in the profile of a giant webpage of "refinements." I'll probably overlap with some of those, but there'll exist a few novel ones here as well.

    New columns in open/save dialogs

    The list view in open and save dialog boxed now supports more than just "Name" and "Date Modified" columns. Right-click on any column to acquire a election of additional columns to display. I've wanted this feature for a long time, and I'm joyous someone finally had time to implement it.

    Configurable columns in open/save dialogsConfigurable columns in open/save dialogs Improved scanner support

    The bundled Image Capture application now has the skill to talk to a wide ambit of scanners. I plugged in my Epson Stylus CX7800, a device that previously required the expend of third-party software in order to expend the scanning feature, and Image Capture detected it immediately.

    Epson scanner + Image Capture - Epson software Enlarge / Epson scanner + Image Capture - Epson software

    Image Capture is also not a wrong miniature scanning application. It has pretty top-notch automatic protest detection, including back for multiple objects, obviating the need to manually crop items. Given the sometimes-questionable character of third-party printer and scanner drivers for Mac OS X, the skill to expend a bundled application is welcome.

    System Preferences bit wars

    System Preferences, like virtually complete other applications in Snow Leopard, is 64-bit. But since 64-bit applications can't load 32-bit plug-ins, that presents a problem for the existing crop of 32-bit third-party preference panes. System Preferences handles this situation with a reasonable amount of grace. On launch, it will pomp icons for complete installed preference panes, 64-bit or 32-bit. But if you click on a 32-bit preference pane, you'll exist presented with a notification like this:

    64-bit application vs. 32-bit plug-in: fight!64-bit application vs. 32-bit plug-in: fight!

    Click "OK" and System Preferences will relaunch in 32-bit mode, which is conveniently indicated in the title bar. Since complete of the first-party preference panes are compiled for both 64-bit and 32-bit operation, System Preferences does not need to relaunch again for the duration of its use. This raises the question, why not possess System Preferences launch in 32-bit mode complete the time? I suspect it's just another passage for Apple to "encourage" developers to build 64-bit-compatible binaries.

    Safari plug-ins

    The inability of of 64-bit applications load 32-bit plug-ins is a problem for Safari as well. Plug-ins are so necessary to the Web experience that relaunching in 32-bit mode is not really an option. You'd probably need to relaunch as soon as you visited your first webpage. But Apple does want Safari to accelerate in 64-bit mode due to some significant performance enhancements in the JavaScript engine and other areas of the application that are not available in 32-bit mode.

    Apple's solution is similar to what it did with QuickTime X and 32-bit QuickTime 7 plug-ins. Safari will accelerate 32-bit plug-ins in divorce 32-bit processes as needed.

    Separate processes for 32-bit Safari plug-insSeparate processes for 32-bit Safari plug-ins

    This has the added, extremely significant capitalize of isolating potentially buggy plug-ins. According to the automated crash reporting built into Mac OS X, Apple has said that the number one understanding of crashes is Web browser plug-ins. That's not the number one understanding of crashes in Safari, intellect you, it's the number one understanding when considering complete crashes of complete applications in Mac OS X. (And though it was not mentioned by name, I reflect they complete know the primary culprit.)

    As you can see above, the QuickTime browser plug-in gets the selfsame treatment as glance and other third-party 32-bit Safari plug-ins. complete of this means that when a plug-in crashes, Safari in Snow Leopard does not. The window or tab containing the crashing plug-in doesn't even close. You can simply click the reload button and give the problematic plug-in another haphazard to role correctly.

    While this is soundless far from the much more robust approach employed by Google Chrome, where each tab lives in its own independent process, if Apple's crash statistics are to exist believed, isolating plug-ins may generate most of the capitalize of truly divorce processes with a significantly less radical change to the Safari application itself.

    Resolution independence

    When they last left Mac OS X in its seemingly interminable march towards a truly scalable user interface, it was almost ready for prime time. I'm sorrowful to philosophize that resolution independence was obviously not a priority in Snow Leopard, because it hasn't gotten any better, and may possess actually regressed a bit. Here's what TextEdit looks like at a 2.0 scale factor in Leopard and Snow Leopard.

    TextEdit at scale factor 2.0 in LeopardTextEdit at scale factor 2.0 in Leopard TextEdit at scale factor 2.0 in Snow LeopardTextEdit at scale factor 2.0 in Snow Leopard

    Yep, it's a bummer. I soundless recollect Apple advising developers to possess their applications ready for resolution independence by 2008. That's one of the few dates that the Jobs-II-era Apple has not been able to hit, and it's getting later complete the time. On the other hand, it's not like 200-DPI monitors are raining from the sky either. But I'd really like to see Apple acquire going on this. It will undoubtedly Take a long time for everything to peek and labor correctly, so let's acquire started.

    Terminal splitters

    The Terminal application in Tiger and earlier versions of Mac OS X allowed each of its windows to exist split horizontally into two divorce panes. This was invaluable for referencing some earlier text in the scrollback while also typing commands at the prompt. Sadly, the splitter feature disappeared in Leopard. In Snow Leopard, it's back with a vengeance.

    Arbitrary splitters, baby!Arbitrary splitters, baby!

    (Now if only my favorite text editor would acquire on board the train to splittersville.)

    Terminal in Snow Leopard also defaults to the novel Menlo font. But ornery to earlier reports, the One exact Monospaced Font, Monaco, is most definitely soundless included in Snow Leopard (see screenshot above) and it works just fine.

    System Preferences shuffle

    The seemingly obligatory rearrangement of preference panes in the System Preferences application accompanying each release of Mac OS X continues in Snow Leopard.

    System Preferences: shuffled yet again Enlarge / System Preferences: shuffled yet again System Preferences (not running) with Dock menuSystem Preferences (not running) with Dock menu

    This time, the "Keyboard & Mouse" preference pane is split into divorce "Keyboard" and "Mouse" panes, "International" becomes "Language & Text," and the "Internet & Network" section becomes "Internet & Wireless" and adopts the Bluetooth preference pane.

    Someday in the far-off future, perhaps Apple will finally arrive at the "ultimate" arrangement of preference panes and they can complete finally proceed more than two years without their muscle reminiscence being disrupted.

    Before affecting on, System Preferences has one smart trick. You can launch directly into a specific preference pane by right-clicking on System Preferences's Dock icon. This works even when System Preferences is not yet running. kindly of creepy, but useful.

    Core location

    One more gift from the iPhone, Core Location, allows Macs to motif out where in the world they are. The "Date & Time" preference pane offers to set your time zone automatically based on your current location using this newfound ability.

    Set your Mac's time zone automatically based on your current location, thanks to Core Location.Set your Mac's time zone automatically based on your current location, thanks to Core Location. Keyboard magic

    Snow Leopard includes a simple facility for system-wide text auto-correction and expansion, accessible from the "Language & Text" preference pane. It's not quite ready to give a dedicated third-party application a accelerate for its money, but hey, it's free.

    Global text expansion and auto-correction Enlarge / Global text expansion and auto-correction

    The keyboard shortcuts preference pane has also been rearranged. Now, instead of a single, long list of system-wide keyboard shortcuts, they're arranged into categories. This reduces clutter, but it also makes it a bit more difficult to find the shortcut you're interested in.

    Keyboard shortcuts: now with categories Enlarge / Keyboard shortcuts: now with categories The sleeping Mac dilemma

    I don't like to leave my Mac Pro turned on 24 hours a day, especially during the summer in my un-air-conditioned house. But I achieve want to possess access to the files on my Mac when I'm elsewhere—at work, on the road, etc. It is feasible to wake a sleeping Mac remotely, but doing so requires being on the selfsame local network.

    My solution has been to leave a smaller, more power-efficient laptop on at complete times on the selfsame network as my Mac Pro. To wake my Mac Pro remotely, I ssh into the laptop, then send the magic "wake up" packet to my Mac Pro. (For this to work, the "Wake for Ethernet network administrator access" checkbox must exist checked in the "Energy Saver" preference pane in System Preferences.)

    Snow Leopard provides a passage to achieve this without leaving any of my computers running complete day. When a Mac running Snow Leopard is set to sleep, it attempts to hand off ownership of its IP address to its router. (This only works with an AirPort Extreme foundation station from 2007 or later, or a Time Capsule from 2008 or later with the latest (7.4.2) firmware installed.) The router then listens for any attempt to connect to the IP address. When one occurs, it wakes up the original owner, hands back the IP address, and forwards traffic appropriately.

    You can even wake some recent-model Macs over WiFi. Combined with MobileMe's "Back to My Mac" dynamic DNS thingamabob, it means I can leave complete my Macs asleep and soundless possess access to their contents anytime, anywhere.

    Back to my hack

    As has become traditional, this novel release of Mac OS X makes life a bit harder for developers whose software works by patching the in-memory representation of other running applications or the operating system itself. This includes Input Managers, SIMBL plug-ins, and of course the dreaded "Haxies."

    Input Managers acquire the worst of it. They've actually been unsupported and non-functional in 64-bit applications since Leopard. That wasn't such a titanic deal when Mac OS X shipped with a whopping two 64-bit applications. But now, with almost every application in Snow Leopard going 64-bit, it's suddenly very significant.

    Thanks to Safari's lack of an officially sanctioned extension mechanism, developers looking to enhance its functionality possess most often resorted to the expend of Input Managers and SIMBL (which is an Input-Manager-based framework). A 64-bit Safari puts a damper on that entire market. Though it is feasible to manually set Safari to launch in 32-bit mode—Get Info on the application in the Finder and click a checkbox—ideally, this is not something developers want to constrain users to do.

    Happily, at least one commonly used Safari enhancement has the top-notch fortune to exist built on top of the officially supported browser plug-in API used by Flash, QuickTime, etc. But that may not exist a feasible approach for Safari extensions that enhance functionality in ways not tied directly to the pomp of particular types of content within a webpage.

    Though I goal to accelerate Safari in its default 64-bit mode, I'll really miss Saft, a Safari extension I expend for session restoration (yes, I know Safari has this feature, but it's activated manually—the horror) and address bar shortcuts (e.g., "w noodles" to peek up "noodles" in Wikipedia). I'm hoping that clever developers will find a passage to overcome this novel challenge. They always seem to, in the end. (Or Apple could add a proper extension system to Safari, of course. But I'm not holding my breath.)

    As for the Haxies, those usually fracture with each major operating system update as a matter of course. And each time, those determined fellows at Unsanity, against complete odds, manage to retain their software working. I salute them for their effort. I delayed upgrading to Leopard for a long time based solely on the absence of my beloved WindowShade X. I hope I don't possess to wait too long for a Snow-Leopard-compatible version.

    The common trend in Mac OS X is away from any sort of involuntary reminiscence space sharing, and towards "external" plug-ins that live in their own, divorce processes. Even contextual menu plug-ins in the Finder possess been disabled, replaced by an enhanced, but soundless less-powerful Services API. Again, I possess faith that developers will adapt. But the waiting is the hardest part.


    It looks like we'll complete exist waiting a while longer for a file system in shining armor to supersede the venerable HFS+ (11 years young!) as the default file system in Mac OS X. Despite rumors, outright declarations, and much actual pre-release code, back for the impressive ZFS file system is not present in Snow Leopard.

    That's a shame because Time Machine veritably cries out for some ZFS magic. What's more, Apple seems to agree, as evidenced by a post from an Apple employee to a ZFS mailing list last year. When asked about a ZFS-savvy implementation of Time Machine, the reply was encouraging: "This one is necessary and likely will approach sometime, but not for SL." ("SL" is short for Snow Leopard.)

    There are many reasons why ZFS (or a file system with similar features) is a flawless appropriate for Time Machine, but the most necessary is its skill to send only the block-level changes during each backup. As Time Machine is currently implemented, if you accomplish a tiny change to a giant file, the entire giant file is copied to the Time Machine volume during the next backup. This is extremely wasteful and time consuming, especially for large files that are modified constantly during the day (e.g., Entourage's e-mail database). Time Machine running on top of ZFS could transfer just the changed disk blocks (a maximum of 128KB each in ZFS, and usually much smaller).

    ZFS would also bring vastly increased robustness for data and metadata, a pooled storage model, constant-time snapshots and clones, and a pony. People sometimes put a question to what, exactly, is wrong with HFS+. Aside from its obvious lack of the features just listed, HFS+ is limited in many ways by its dated design, which is based on HFS, a twenty-five year-old file system.

    To give just one example, the centrally located Catalog File, which must exist updated for each change to the file system's structure, is a frequent and inevitable source of contention. Modern file systems usually spread their metadata around, both for robustness (multiple copies are often kept in divorce locations on the disk) and to allow for better concurrency.

    Practically speaking, reflect about those times when you accelerate Disk Utility on an HFS+ volume and it finds (and hopefully repairs) a bunch of errors. That's bad, okay? That's something that should not betide with a modern, thoroughly checksummed, always-consistent-on-disk file system unless there are hardware problems (and a ZFS storage pool can actually deal with that as well). And yet it happens complete the time with HFS+ disks in Mac OS X when various bits of metadata acquire corrupted or become out of date.

    Apple gets by year after year, tacking novel features onto HFS+ with duct tape and a prayer, but at a unavoidable point there simply has to exist a successor—whether it's ZFS, a home-grown Apple file system, or something else entirely. My fingers are crossed for Mac OS X 10.7.

    The future soon

    Creating an operating system is as much a gregarious exercise as a technological one. Creating a platform, even more so. complete of Snow Leopard's considerable technical achievements are not just designed to capitalize users; they're also intended to goad, persuade, and otherwise herd developers in the direction that Apple feels will exist most advantageous for the future of the platform.

    For this to work, Snow Leopard has to actually find its passage into the hands of customers. The pricing helps a lot there. But even if Snow Leopard were free, there's soundless some cost to the consumer—in time, worry, software updates, etc.—when performing a major operating system upgrade. The selfsame goes for developers who must, at the very least, certify that their existing applications accelerate correctly on the novel OS.

    The accustomed passage to overcome this kindly of upgrade hesitation has been to pack the OS with novel features. novel features sell, and the more copies of the novel operating system in use, the more motivated developers are to update their applications to not just accelerate on the novel OS, but also Take advantage of its novel abilities.

    A major operating system upgrade with "no novel features" must play by a different set of rules. Every party involved expects some counterbalance to the lack of novel features. In Snow Leopard, developers stand to gleam the biggest benefits thanks to an impressive set of novel technologies, many of which cover areas previously unaddressed in Mac OS X. Apple clearly feels that the future of the platform depends on much better utilization of computing resources, and is doing everything it can to accomplish it simple for developers to run in this direction.

    Though it's obvious that Snow Leopard includes fewer external features than its predecessor, I'd wager that it has just as many, if not more internal changes than Leopard. This, I fear, means that the initial release of Snow Leopard will likely suffer the typical 10.x.0 bugs. There possess already been reports of novel bugs introduced to existing APIs in Snow Leopard. This is the exact opposite of Snow Leopard's implied covenant to users and developers that it would concentrate on making existing features faster and more robust without introducing novel functionality and the accompanying novel bugs.

    On the other side of the coin, I imagine complete the teams at Apple that worked on Snow Leopard absolutely reveled in the occasion to polish their particular subsystems without being burdened by supporting the marketing-driven feature-of-the-month. In any long-lived software product, there needs to exist this kindly of release valve every few years, lest the entire code foundation proceed off into the weeds.

    There's been one other "no novel features" release of Mac OS X. Mac OS X 10.1, released a mere six months after version 10.0, was handed out for free by Apple at the 2001 Seybold publishing conference and, later, at Apple retail stores. It was also available from Apple's online store for $19.95 (along with a copy of Mac OS 9.2.1 for expend in the Classic environment). This was a different time for Mac OS X. Versions 10.0 and 10.1 were slow, incomplete, and extremely immature; the transition from classic Mac OS was far from over.

    Judged as a modern incarnation of the 10.1 release, Snow Leopard looks pretty darned good. The pricing is similar, and the benefits—to developers and to users—are greater. So is the risk. But again, that has more to achieve with how horrible Mac OS X 10.0 was. Choosing not to upgrade to 10.1 was unthinkable. Waiting a while to upgrade to Snow Leopard is reasonable if you want to exist positive that complete the software you custody about is compatible. But don't wait too long, because at $29 for the upgrade, I anticipate Snow Leopard adoption to exist quite rapid. Software that will accelerate only on Snow Leopard may exist here before you know it.

    Should you buy Mac OS X Snow Leopard? If you're already running Leopard, then the retort is a resounding "yes." If you're soundless running Tiger, well, then it's probably time for a novel Mac anyway. When you buy one, it'll approach with Snow Leopard.

    As for the future, it's tempting to view Snow Leopard as the "tick" in a novel Intel-style "tick-tock" release strategy for Mac OS X: radical novel features in version 10.7 followed by more Snow-Leopard-style refinements in 10.8, and so on, alternating between "feature" and "refinement" releases. Apple has not even hinted that they're considering this sort of plan, but I reflect there's a lot to recommend it.

    Snow Leopard is a unique and resplendent release, unlike any that possess approach before it in both scope and intention. At some point, Mac OS X will surely need to acquire back on the bullet-point-features bandwagon. But for now, I'm content with Snow Leopard. It's the Mac OS X I know and love, but with more of the things that accomplish it feeble and offbeat engineered away.

    Snowy eyes Looking back

    This is the tenth review of a complete Mac OS X release, public beta, or developer preview to accelerate on Ars, dating back to December 1999 and Mac OS X DP2. If you want to jump into the Wayback Machine and see how far Apple has approach with Snow Leopard (or just want to bone up on complete of the titanic cat monikers), we've gone through the archives and dug up some of their older Mac OS X articles. contented reading!

  • Five years of Mac OS X, March 24, 2006
  • Mac OS X 10.5 Leopard, October 28, 2007
  • Mac OS X 10.4 Tiger, April 28, 2005
  • Mac OS X 10.3 Panther, November 9, 2003
  • Mac OS X 10.2 Jaguar, September 5, 2002
  • Mac OS X 10.1 (Puma), October 15, 2001
  • Mac OS X 10.0 (Cheetah), April 2, 2001
  • Mac OS X Public Beta, October 3, 2000
  • Mac OS X Q & A, June 20, 2000
  • Mac OS X DP4, May 24, 2000
  • Mac OS X DP3: crucible by Water, February 28, 2000
  • Mac OS X Update: Quartz & Aqua, January 17, 2000
  • Mac OS X DP2, December 14, 1999

  • Mozilla ends Firefox back for Mac OS Tiger | killexams.com real questions and Pass4sure dumps

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    Next Firefox to drop Mac OS X 10.4 back | killexams.com real questions and Pass4sure dumps

    Mozilla has officially decided that the next major version of Firefox will require at least Mac OS X 10.5 when running on Apple computers.

    "We believe a Mac OS X 10.5 minimum will allow us to provide the best experience feasible to their users," Mozilla Mac programmer Josh Aas said Tuesday in a mailing list announcement. Firefox is built on a browser engine called Gecko, and the upcoming version 1.9.3 will possess technology for Mac OS X 10.4 and before removed, he said.

    The recently released Firefox 3.6 works on Mac OS X 10.4, aka Tiger. Mozilla will back it for some months after the browser's replacement version is issued, which means 10.4 back should continue into 2011.

    Aas ran into some resistance earlier this month when he announced Mozilla's crave to drop Mac OS X 10.4 support. In a divorce mailing list comment, Mozilla's Asa Dotzler expressed some enthusiasm for trying to embolden people to upgrade.

    "It's like a public health issue. Internet-connected computers that are not kept up to date and secure are almost guaranteed to acquire compromised and those infected machines are used to assault the repose of the Internet users with spam, more malware, or DDOSes," Dotzler said, referring to distributed denial-of-service attacks. "It's not just a personal election and as stewards of a vigorous Internet, Mozilla is in a unique position to thrust this kindly of messaging. We're not trying to sell people novel hardware or software or worthless anti-virus measures, so they should exist able to communicate this well without people assuming some ulterior (profit) motive."

    Mozilla is working on an update to Firefox 3.6, which uses Gecko 1.9.2, that puts plug-ins such as Adobe glance and Microsoft Silverlight into a divorce reminiscence location in an effort to augment stability. The group hopes to release a beta version of that Firefox version by the terminate of March.

    Separately, Mozilla is working on Gecko 1.9.3 and plans to issue a novel alpha release of the software this week.

    Correction at 9:55 a.m. PST: The headline has been fixed to reflect the proper version of Mac OS X.

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