Mar 142010

Yes, yes, I know what you’re thinking… sure , boot with 6 and 4 pressed and your Mac will boot in 64 bit mode.

But I’m talking aout the other way around: haveing your modern MacBook booting in 64 bit mode, and possibly turn it into 32 bit only when you need it (sure, by keeping 3 and 2 pressed while booting).

Here’s howto:

  1. Check your Mac is capable of doing it by issuing in terminal the command:
    ioreg -l -p IODeviceTree | grep firmware-abi
  2. If output is something like “| |   “firmware-abi” = <“EFI64”>” this means Yes, you can!
  3. Open a Terminal and cd to /Library/Preferences/SystemConfiguration/
  4. edit
  5. under Kernel Flags insert
    between the <string> and </string> tags
  6. reboot
  7. Enjoy

Of course, a good pre-check if you could be fine is to boot keeping pressed 6 and 4… if it boots 64bit then you’re ok.