How To Make Your Mac Boot In 64-bit Mode

Apple likes to claim that Mac OS X is the world’s most advanced operating system. While that claim may or may not be true, one thing is certain that it definitely is among the finest desktop operating systems in use today.

For all it’s technical and visual appeal, there are still some areas where Mac OS X is quite a bit behind it’s competitors such as Linux and Windows. One such shortcoming of OS X that I can think of is lack of a 64-bit mode, by default.

Now, let me be clear on this. Mac OS X does support 64-bit applications and most of it’s user-land applications actually do run in 64 bit. It’s the kernel that boots up in 32-bit mode, mostly. It’s a complicated affair really and if you have a modern Mac, it most probably is 64-bit compatible and even though it boots up the 32-bit kernel, by default, today I’ll teach you to boot it in 64-bit mode.

What kernel am I on anyway ?

To find out the bitness of your Mac’s currently running kernel, launch the System Profiler application and scroll down to the software list in the contents pane.

If it displays a “Yes” against 64-bit kernel and extensions, that means you’re already running a 64-bit system, if not, read on to find out how to move to one.

The Easy (and temporary) way

One way you can make your Mac boot up with a 64-bit kernel is to press the “6” and “4” keys together when the computer is booting up. This will make Mac OS X select the 64-bit kernel to boot up and is helpful if you just want to test if all your applications work correctly in 64-bit mode. The change is temporary and the next time you reboot, the kernel will be back to 32-bit.

The Permanent Fix

If all your applications work fine in 64-bit mode and you’d like to move permanently to it, you have to make a few changes to the boot files of your Mac.

Edit the fileĀ found in /Library/Preferences/SystemConfiguration. Use a plain text editor for this. I’d suggest something like MacVim or TextWrangler for the task.

Add the following string exactly as shown, right below the line that says <key>Kernel Flags</key>.


The file after the change should look like this

That’s it. The next time you boot, your Mac should boot up in 64-bit mode by default.