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My mac has 64-bit EFI, but it only boots with 32-bit kernel

Why isn't my MacBook running 64 bit mode? It's a mid-2010 model, "MacBook 7,1" , with a Core-2 Duo. why would it run in 32-bit mode? Could it be because I've only got 2GB of RAM?

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I don't think these machines booted into 64bit. (the new macbook pros do).

You can hold down 6 and 4 whilst rebooting for a temporary 64bit boot (if available)

If that works, you can try this in terminal and then reboot

sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.Boot 'Kernel Flags' 'arch=x86_64'

This will make the mac boot in 64bit mode by default.

  • Are there any negative side effects to booting into 64-bit mode?
    – Moshe
    Apr 18 '11 at 5:58
  • The 64-bit versions of apps take slightly more RAM because they need to hold 64-bit addresses instead of 32-bit. This is only a very minor difference. I can't think of anything else though.
    – wjl
    Apr 18 '11 at 5:59
  • like your tip of holding down 6 and 4 key at bootup
    – I-M-JM
    Apr 18 '11 at 6:08
  • I don't think this will work for non-Pro MacBooks.
    – ghoppe
    Apr 18 '11 at 8:02
  • Ah yes. Misread that it wasn't a pro.
    – robzolkos
    Apr 18 '11 at 8:46

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