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MillimeterApple Snow Leopard for Video Producers, Part 1
Sep 24, 2009 12:00 PM, By Jan Ozer
Figure 1 (from Wikipedia). The operating system kernel.
What's an Operating System Kernel?
Now let's dive into one of the most significant Snow Leopard advances: the existence of a true 64-bit kernel. According to Wikipedia, "In computing, the 'kernel' is the central component of most computer operating systems. Its responsibilities include managing the system's resources (the communication between hardware and software components)."
Figure 1, also from Wikipedia, illustrates this definition. Starting with Panther (OS X 10.3), Apple introduced 64-bit features into the OS, but the kernel remained 32-bit, as did device drivers and other low-level routines. The first application above the kernel was a 64-bit version of Unix, which enabled Macs to address far more than the 32-bit limit of 4GB. This also enabled 32-bit programs to run in their own 4GB of memory. With memory-intensive applications such as Final Cut Pro, that kind of breathing room can deliver profound performance increases, which is the low-hanging fruit of 64-bit OS performance enhancements.
Though Snow Leopard is the first true 64-bit Mac OS, Leopard delivered one of the key benefits of a 64-bit OS, enabling 4GB of working space for 32-bit programs and the ancillary performance boost. This doesn't mean that Snow Leopard won't deliver some immediate performance benefits; as mentioned above, I found speed improvements of up to 30 percent in my initial tests. But it likely won't deliver exponential performance benefits in day-to-day, real-world tests, at least at first. Down the road, however, as developers release 64-bit apps that leverage Grand Central Dispatch and OpenCL, Snow Leopard will pay huge performance dividends.
In this regard, Snow Leopard is more of a road map than an immediate destination. It's a line in the sand that going forward, all serious Mac applications will be 64-bit apps, and we've probably seen the last 32-bit release of Final Cut Studio. That would be my guess, anyway.
Figure 2. Here's where you tell which kernel you're running.
The Immediate Reality of 64-bit Computing
But, I get ahead of myself. In the short term, 32-bit computing is still very much with us; otherwise, you'd lose the ability to work with all those devices —scanners, printers, card readers, optical disc drives, and the like—that rely on 32-bit drivers. That's because the 64-bit kernel can't work with 32-bit drivers, which is why Apple shipped Snow Leopard with two kernels—one 32-bit, one 64-bit—and runs the 32-bit kernel by default on all computers except certain Xserve workstations.
It's a sound decision, since most users would be frustrated if they upgraded and lost the use of their key peripherals. It's just not one of those details that is startlingly obvious when you read Apple's marketing literature.
To run the OS in 64-bit mode, hold down the 6 and 4 keys when booting your Snow Leopard-upgraded Mac. It will remain in 64-bit mode for subsequent startups until you hold down the 3 and 2 keys while booting. To determine which kernel is running, check System Profiler (click About this Mac, then the More Info button) and click the Software profile.
If you install Snow Leopard, try working in 64-bit mode and see if any of your peripherals "break." I had no problem with either of my tested computers, but I am a Mac/Windows shop and most of my peripherals are Windows-based.
Note that I did see significant differences between performance in 64-bit and 32-bit modes, but it's all over the map at this point. I'm sure the results will come together as I finish my testing. Next time, I'll share performance comparisons of Leopard vs. Snow Leopard in 32-bit and 64-bit modes.
So let's summarize the 64-bit findings. Though Snow Leopard is the first Mac OS with a 64-bit kernel, it's not the first that lets 32-bit programs run in their own 4GB memory spaces, which provides the bulk of the performance advantage over 32-bit operating systems. So don't expect a performance miracle.
To retain compatibility with 32-bit peripherals, Snow Leopard runs in 32-bit mode by default. You can easily switch back and forth, but if you haven't manually forced yourself into 64-bit mode, you've probably been running in 32-bit mode.
Now let's briefly discuss two additional new features in Snow Leopard that will pay performance dividends down the road. First is Grand Central Dispatch.
Continue the discussion on “Crosstalk” the Millimeter Forum.