Review: Apple's Snow Leopard opens door to a fab future

The use of 64-bit computing will greatly improve the capabilities of computers. For example, 32-bit software can access only 4 GB of RAM at a time; 64-bit computing expands that ceiling to 16 exabytes. That's 16 billion gigabytes. Plus, 64-bit applications run faster on computers with Intel Core 2 Duo or Xeon processors. They can crunch 64-bit code twice as fast per clock cycle as computers running in 32-bit.

Apple touts Snow Leopard as being first Mac OS to finally support 64-bit from top to bottom, although the default kernel status for all consumer Macs is the 32-bit kernel. Snow Leopard supports 64-bit applications even while running 32-bit drivers. Basically, whether the machine is booted into the 32-bit kernel or the 64-bit kernel, any application that can run at 64-bit will run in that mode automatically.

By having Snow Leopard boot into the 32-bit kernel, Apple improves software compatibility. That's because kernel extensions must match the kernel's mode, or they don't work. While Apple did a fine job porting over its native applications for 64-bit compatibility, there are still some third-party vendors that haven't released updates for their software (such as the aforementioned Cisco VPN software) yet.

OpenCL, GPUs and Grand Central Dispatch

Another technology new to Snow Leopard is the OpenCL standard (download PDF), which promises to speed things up without any changes to your hardware needed.

While CPU manufacturers have shifted from increasing processor clock speeds to adding more cores to processors, graphics chip makers have continued pushing the boundaries to boost the processing power behind their graphics cards. Years ago, Apple began offloading animation effects from the CPU to the graphics processing unit (GPU), freeing up the main processors for actual data-crunching.

Every version of Mac OS X in recent years has increasingly utilized the GPU for computationally expensive tasks. In 2006, Apple unveiled Core Image and Core Animation with Mac OS X 10.4, technologies that allow real-time image and video effects to be handled by the graphics cards. With Snow Leopard, Apple takes GPU acceleration to another level by developing and publishing an open standard to offload even more work to GPUs.

Enter OpenCL, a language and runtime framework that allows developers to crunch any data-parallel algorithms on any free processing core, automatically, without needing to code for specific circumstances. The best part for Mac owners is that OpenCL works with all GPUs and CPUs available in Apple's current line-up. The best part for developers is that only the most performance-intensive aspects of their software need be rewritten to take advantage of the new technology.

While OpenCL bridges the gap between software and the available processing cores on a computer, the new problem is how to account for all these cores and software instruction threads.

That's where Grand Central Dispatch (GCD) comes in.

Grand Central Dispatch is the foundation for keeping everything running smoothly; it acts like a built-in air traffic control center, dynamically adjusting computer workload based on available hardware and resources. If the resources are available, GCD speeds things up. If the computer is busy, GCD backs off. In concert with OpenCL and 64-bit, Grand Central Dispatch should lead to a big jump in performance and optimization as applications are updated.