How to tell if you’re running the 32 bit or 64 bit kernel in Mac OS X Snow Leopard
10.6, Command Line, Mac OS X, Snow Leopard - September 7th, 2009 - 11 Comments
Snow Leopard 10.6 is the first Mac OS X version to ship with a 64 bit kernel, and obviously your Mac has to have a 64 bit processor to utilize that kernel, but some 64 bit Mac’s are not defaulting to the 64 bit kernel. So how do you know which kernel version your machine is using? The command to determine if you are using a 32 bit kernel or a 64 bit kernel is the same, it’s the output that will tell you which kernel version you are using.
Open the Terminal and type the following command:
uname -a
If you’re using a 32 bit Kernel in Mac OS X:
iMac:~ user$ uname -a
Darwin iMac.local 10.0.0 Darwin Kernel Version 10.0.0: Fri Jul 31 22:47:34 PDT 2009; root:xnu-1456.1.25~1/RELEASE_I386 i386
see the i386 on the end there? That indicates it’s the 32 bit kernel
If you’re using a 64 bit Kernel in Mac OS X:
iMac:~ user$ uname -a
Darwin iMac.local 10.0.0 Darwin Kernel Version 10.0.0: Fri Jul 31 22:47:34 PDT 2009; root:xnu-1456.1.25~1/RELEASE_X86_64 x86_64
the x86_64 at the end will let you know you are using the 64 bit kernel.
You can alternate between the two by holding down “6″ and “4″ during system boot to load the 64 bit kernel, or holding down ‘3′ and ‘2′ during boot to use the 32 bit kernel. Your machine should default into the kernel that is best supported.
Actually, all Macs except for the Xserve default to the 32bit kernel. This is justified since the Xserve is a specialized piece of equipment where you can be sure all device drivers are built as 64bit. For the consumer line, that can’t always be assumed, so its safer to play with the 32bit kernel even while running 64bit apps.
The other easy to tell which kernel you’re running is by opening System Profiler and clicking on Software. In the overview it will list 64-bit Kernel and Extensions. Odds are it will say no, signifying you’re using the 32bit kernel. Your machine needs to have 64bit EFI, which only the newest Macs have. If you want to check for that use: ioreg -l -p IODeviceTree | grep firmware-abi. The result will show either EFI32 or EFI64 depending on what you have.
Only the server version of OSX lets you switch to 64 bit, I tried the toggle above, it doesn’t work. The Apple tech notes say this very clearly. I have a 64-bit EFI on my v1 MacBook Air, but this makes no difference to booting.
Is there a way to test if applications are truly running in 64 bit? Apple claims that “Nearly all system applications — including the Finder, Mail, Safari, iCal, and iChat — are now built with 64-bit code”. So the kernal runs in 32 bit but the apps run in 64 bit?
I tried the toggle and it does indeed work. The iMac booted OS X 10.6 into 64 bit mode and now some of my system preferences and kernel extension no longer work.
http://www.flickr.com/photos/islandinthenet/3897219777/
look under About this Mac/More info…/Software to see if there is a Yes or No in the line about 64 bit Kernal extensions.
So, there are 3 tests you can run, according to the above article & comments. When I run them I get differing results.
uname test:
Darwin dunnb.local 10.3.0 Darwin Kernel Version 10.3.0: Fri Feb 26 11:58:09 PST 2010; root:xnu-1504.3.12~1/RELEASE_I386 i386
ioreg test:
“firmware-abi” =
System profiler:
64-bit Kernel and Extensions: No
Also, it appears that holding down the “6″ and the “4″ keys while rebooting has no effect.
ioreg test should say:
“firmware-abi” = <”EFI64″>
I have the newest Core i7 MacBook Pro and its kernel is running in 32-bit also. I feel it is still dog slow running Aperture 3 and multiple apps at once. I dropped $2.2k in order to run Aperture 3 better but have not seen much performance increase, especially since my plugins require it to run in 32-bit mode still.
So is running the 64-bit kernel safe/stable to do, and if so how?
Get more RAM, more RAM helps the most for Aperature speed. You can run the 64 bit kernel it won’t hurt anything, but if a plugin requires 32bit it will prevent the 64bit Aperature from loading (I think).
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Just booted up my 27* in 64 bit mode and i thought it was in 32 bit its just got quicker esp loading my iphoto and itunes libs. Thanks for the info on how to do this. Its sites like these that let the average pc user get the most and best experience from their machines