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Following on from Are the new Macbook Pro 64 bit or 32 bit?. The new MacBook Pros (March 2011) now seem to start in 64bit mode rather than 32bit mode. Thanks for letting us know Apple!

This is causing us a problem with our Cisco VPN client as it uses a 32bit kernel extension that naturally doesn't work when booted into 64bit mode.

Holding down 3 & 2 will start the machine into 32bit mode and the VPN client works fine, but when we reboot the Mac it starts up again into 64bit mode.

How can we ensure that the Macs start in 32bit mode.

(Sure getting a 64bit Cisco VPN client is a better day)

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up vote 6 down vote accepted

To select the 32-bit kernel for the current startup disk, use the following command in Terminal:

sudo systemsetup -setkernelbootarchitecture i386

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I would expect that sudo nvram boot-args=arch=x86 would work. You should also be able to edit /Library/Preferences/SystemConfiguration/ (which is an XML format property list normally; if not, see plutil) and set the Kernel Flags key to arch=x86. Note that losing the NVRAM contents will clear the former and Apple system updates might conceivably overwrite the latter. approaches it from the other direction (making a Mac boot in 64-bit mode by default); just use x86 for 32-bit mode.

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