My MacOS X

Users who want to run the new 64-bit kernel on late-model Macs (pretty much anything released after early 2008) can do so by booting with the 6 and 4 keys held down. If you’re wondering whether your Mac has a 64-bit EFI firmware, you can type this command in Terminal:

# ioreg -l -p IODeviceTree | grep firmware-abi

The response will identify the machine as either having 32-bit or 64-bit EFI.

To boot 64-bit kernel every time you boot machine:

1. Print nvram settings

# sudo nvram -p

2. Set boot-args to use 64 bit kernel

# sudo nvram boot-args="arch=x86_64"

Don’t forget to add in your existing boot-args to the command above. Using nvram means you don’t need to have to remember to hold down 6 or 4 during booting each time. To go back to the 32 bit kernel, just set the boot-args using nvram without the arch=x86_64 option.