64-bit OS X Snow Leopard defaults to 32-bit kernel
Why?
It defaults to the 32-bit kernel on bootup because not all software you may have may be compiled / designed for 64-bit. Moving from 32 to 64 is a gradual process. 64-bit applications can still take advantage of being 64-bit and using multiple cores, but the kernel itself is still 32-bit by default. Only Snow Leopard Xserve boots into 64-bit kernel by default.
How do you change this?
If you have a machine capable of 64-bit processing, and you’re bold enough to go 64 only, hold down 6 and 4 on boot up. It will make the machine boot up in 64-bit kernel mode – but be ready for 32-bit applications to break.
Here’s how you find out if you’re machine is capable of 64-bit processing:
http://support.apple.com/kb/HT3696
