How to Check and See If Your Mac Runs 64-Bit

I’m running Mac OS 10. 6. 4 on my Mac Pro, and I’m confused about 32-bit and 64-bit.

I’m running Mac OS 10.6.4 on my Mac Pro, and I’m confused about 32-bit and 64-bit. What will happen if I restart my Mac holding the 6 and the 4 keys down to boot up into 64-bit? Nobody seems to know at my Mac User Group, so I’d love to share your answer with them.

When you hold down the 6 and 4 keys on the keyboard during a bootup cycle, you are manually forcing your Intel Mac to search for a 64-bit version of the EFI firmware and subsequently boot into 64-bit Mac OS X, if your computer supports 64-bit.

With a 64-bit system, information can be processed much faster because the processor can handle 64-bit chunks of data, instead of 32-bit chunks. In 32-bit mode, an application can only address up to 4GB of memory, while the 64-bit mode allows for memory addressing of up to a theoretical 16EB (each exabyte is 1 billion gigabytes).

My Mac's firmware is 64-bit...

...but I'll stick to 32-bit to avoid problems with incompatible kernal extensions.

Apple currently supports both 32-bit and 64-bit systems with Snow Leopard (Mac OS 10.6), but today’s Macs automatically boot into 32-bit mode because some OS X kernel extensions still aren’t 64-bit compatible. Unless you have a specific computing need for a 64-bit system, you may want to boot using the 32-bit mode to avoid software incompatibilities. Press 3 and 2 the next time you boot your Mac to return to the 32-bit mode.
You can check to see if your Mac supports 64-bit mode by typing the following into the Terminal and pressing Enter:

ioreg -l -p IODeviceTree | grep firmware-abi

The response will tell you either 32-bit or 64-bit EFI. Then open System Profiler (/Applications/Utilities) and select Software from the Contents list on the left to see whether or not the version of Mac OS X supports 64-bit Kernel and Extensions. Currently this is not supported with Mac OS 10.6.4.

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