Mac OS X: 64-bit kernel frequently asked questions

How do I tell if I'm using the 64-bit kernel?

Use the System Profiler to determine if you're running a 64-bit kernel.

1. From the Apple () menu, choose About this Mac, then click More Info. 
2. In the Contents pane, select Software. 
3. If 64-bit Kernel and Extensions is set to Yes, you are running a 64-bit kernel.

Note: A 64-bit kernel is not the same thing as a 64-bit processor.

Does running a 64-bit kernel have an impact on applications I usually run?

No, but it can have a significant impact on kernel extensions, usually used to enable third-party product hardware and special features.  32-bit kernel extensions will not work when your computer is running a 64-bit kernel.  Products that use 32-bit kernel extensions may not work or may not recognize their associated hardware.   Learn more about compatibility with the 64-bit kernel.

Can I switch between the 64-bit kernel and 32-bit kernel?

If you are using OS X Mountain Lion, switching to a 32-bit kernel is not supported. Mountain Lion uses 64-bit mode.

OS X Lion and earlier versions of OS X support a 32-bit kernel. Switching to the 32-bit kernel allows you use products that use 32-bit kernel extensions.

Can I find out if a kernel extension is 32-bit?

Yes.

1. From the Apple () menu, choose About this Mac, then click More Info. 
2. In the Contents pane, select Extensions.  It may take a few moments for all your extensions to be listed. 
3. Look in the 64-Bit column to determine if an kernel extension is 64-bit compatible.  If it is, the entry will be Yes.

Which Apple products ship with a 64-bit kernel as the default configuration?

A list of Macs that use the 64-bit kernel is available here.