How To: Enable 64-bit As Default In OS X Snow Leopard

The latest version of Apple's Mac OS X "Snow Leopard" will be released on August 28th, 2009. Those of us who will be upgrading, or are using build 10A432, which is the "Golden Master", may realize that by default, 64-bit kernel and extensions is not enabled.

If you are running Snow Leopard, or when you do run Snow Leopard, you will notice on all machines except for XServe machines, that 64-bit kernel and extensions will look like this in System Profiler:



As you can see, 64-bit Kernel and Extensions is currently saying No.

Also, you may know that you can enable 64-bit Kernel on some (capable) machines by holding the "6" and "4" keys at boot. This will only work on (capable) machines, and those machines must have a 64-bit EFI.

To check which EFI version you have, type this into Terminal:

And you will see either "EFI32" or "EFI64" returned to you.

If you have "EFI32" returned, you cannot enable 64-bit Kernel and Extensions, but you are still able to run 64-bit Applications.

Now, you can either continue to hold "6" and "4" everytime you want to boot, or you can do the following:

Navigate to the following location in Finder:

From there, find this bit of text:

And add arch=x86_64 between the <string> tags, so that you have this:

Save the file, and reboot your machine. If you have a (capable) Mac, you will see "Yes" in System Profiler, instead of "No".

If you want to boot into 32-bit, just hold "3" and "2" at boot, or edit the file again, and remove that string.

Hopefully this helps some of us with a Mac and Snow Leopard.

Cheers!

Edit: I have realized, that in System Profiler, it may still display "No".

You can check if you are running 64-bit by default, by checking Activity Monitor, and next to each process, if it's enabled as 64-bit, it will say "Intel (64-bit)".

This would not be displayed if you were not running the 64-bit kernel, to my knowledge.

You can also view it in System Profiler by clicking "Extensions", which will display most, if not all, of them as 64-bit enabled.



The above shot, shows the Extensions pane, and at the bottom of it, it says "Architectures", and states the x64 kernel being loaded. Also, to the right of all of them (almost), it says 64-bit (Intel), and says YES next to them.
Edited by halifax1 - 8/25/09 at 5:51am

Make sure to check out my edit, as mine still states as "No", but if I boot in Verbose Mode (Command+V), the first piece of dialog states the kernel I've stated to run, as well as "64-bit Enabled" near the first bit of text, so it is indeed running the 64-bit kernel and extensions.

I'll update the OP with a few more shots showing it.

Thanks to you to remind me about holding 6 and 4, I decided to figure out how to default for it!

Running 64-bit still runs all 32-bit programs.