Snow Leopard moves the entire Mac operating system to a 64-bit architecture. Mac users may feel a bit ho-hum about this. After all, we have enjoyed 64-bit processors since the G5 line of PowerPC Macs. However, while the G5 processor used a 64-bit architecture, its RAM space was limited to 4 TB (terabytes), a 42-bit RAM bus. The existing operating systems, Tiger and Leopard, used a 32-bit kernel and drivers, although they did support 64-bit processes.
Snow Leopard Technology: 64-bit OS
With Snow Leopard, Apple is moving the entire OS to a 64-bit architecture. This includes a new 64-bit kernel and drivers, new 64-bit Cocoa, and a complete 64-bit system and application space. Snow Leopard will still be able to run 32-bit applications because it retains a 32-bit apps space, and 32-bit Cocoa and Carbon frameworks. Almost any application that could run under Tiger should be able to run without issue under Snow Leopard.
Snow Leopard Technology: 64-bit RAM Space
The move to a 64-bit OS will remove the current 4 GB of RAM per process memory limit and instead put a mind-numbing 16 exabytes (that’s 16 billion gigabytes) at an application’s disposal. Of course no Mac can currently support 16 exabytes of RAM. Even if it could, the cost would be astronomical. Still, breaking the 4 GB barrier will bring new generations of applications to the Mac.
“But wait,” you say. “My Mac already has 8 GB or more of RAM and it seems to be able to use it just fine, thank you very much.” You’re exactly right. Your Mac can easily use all of that additional RAM, but any single process can only use 4 GB of RAM.
So, what’s your Mac going to do with all of those extra memory capabilities? Well, not much. Snow Leopard has a small footprint, so it shouldn’t be much of a memory hog. But what various applications can do with the extra memory capabilities is another question entirely. One application that comes to mind is Adobe Photoshop. When Adobe releases a 64-bit version of Photoshop for the Mac, the current memory limit for working with images should be gone, allowing you to work directly with very high resolution images without being forced to use slower scratch space to perform editing or other tasks. Applications that need to work with large sets of data points, such as databases and scientific applications, will be able to access those data points from fast RAM, not slow disk space, which will significantly speed up processes.
Snow Leopard Technology: 64-bit Speed
Even 64-bit applications don’t always execute instructions that are 64 bits in length. Far from it. Most instructions only need a nibble (4 bits), byte (8 bits), word (16 bits), or long word (32 bits) of the available 64 bits, leaving a lot of unused bits per instruction executed. Snow Leopard, in combination with Intel processors, can pack two instructions per execution cycle (when space permits), dramatically speeding up performance. This won’t double performance, but it will produce a noticeable gain.
Snow Leopard Technology: 64-bit Security
Often overlooked, one aspect of moving to a full 64-bit OS is an increase in system security. How does a 64-bit OS affect security? It should eliminate one of the most common forms of security threats, or at least nullify it until malware developers come up with something new. Snow Leopard, and any application that runs under Snow Leopard, will set all writeable memory as non-executable.
What this means is that one of the common methods used to gain control of a computer, the injection of arbitrary code into the memory used by an application, will become ineffectual. Because all writeable memory will be marked as non-executable, any instructions found there would not be run by the OS or any applications.
The larger available RAM space is an additional security benefit. Apple tried to make use of ASLR (Address Space Layout Randomization) in Leopard. With ASLR, the location of an application’s memory is randomly selected from available memory each time the application is run. But since the available memory space in Leopard was limited to 4 GB, Apple ended up having to retain certain dynamic loaders that were responsible for loading and unloading frameworks, and the libraries applications need, in the same memory space all the time, which made their location easy to find and attack. With the larger 64-bit memory space available, Apple will use a better ASLR that will include randomized locations for those dynamic loaders as well.
Together, these two security features of Snow Leopard’s 64-bit architecture should make Snow Leopard a more difficult target for malware developers.
