About this Mac > ( More Info ) > Software
System Software Overview:
System Version: Mac OS X 10.6.8 (10K549)
Kernel Version: Darwin 10.8.0
Boot Volume: X-Drive
Boot Mode: Normal
Computer Name: Grants-MacPro
User Name: Grant (grant)
Secure Virtual Memory: Not Enabled
64-bit Kernel and Extensions: Yes <
Time since boot: 10:38
4GB of RAM per processor core - this has no standing.
32-bit processes address up to 4GB address space
There is an urban legend rule of thumb of how much physical memory you want for a dual processor quad core (or dual core etc) but that has no bearing.
64-bit kernel mode is separate from the OS and does allow processes to work with large address spaces.
Should you boot into the 64-bit kernel?
Tests of photographic applications show that the gains of booting with the 64-bit kernel can be substantial, keeping in mind that a 30% gain via hardware often costs several thousand dollars more. Why not get a good chunk of that for about $25?
Your 64-bit programs (if any) will run fine on a 32-bit kernel, gaining the benefits of 64-bit-ness. But they won’t see full performance that way.
The reason not to boot into 64-bit mode is compatibility with software drivers of various kinds. Apple really can’t be faulted here, but you can make an intelligent choice for yourself. You’ll want to verify if your software has any issues in 64-bit mode.; one way is simply to try it.
Does your Mac have 64-bit EFI firmware? PERMALINK
You Mac might be a few years old and have 32-bit EFI firmware (the code that runs to boot the Mac). See this Apple tech note for which machines can boot the 64-bit kernel
With 32-bit firmware, you cannot boot into 64-bit kernel; it’s not possible.