Processors

Understanding 32- versus 64-bit differences in Snow Leopard

Erik Eckel clears up some misinformation about how Mac Snow Leopard handles 32- and 64-bit processing. Find out which systems are 64-bit capable and what tweaks you can make.

Apple touts Mac Snow Leopard's 64-bit capacity. And, many technology professionals believe that, whenever they boot their Intel-powered Snow Leopard systems, they're automatically booting into a full 64-bit environment. They may be wrong.

According to Apple, Early 2009 and Early 2008 versions of Xserve boot automatically, by default, using a 64-bit kernel. Other Snow Leopard systems, including Mac Pros and Mac laptops, do not. Instead, the 6 and 4 keys must be held down while booting to enable the 64-bit kernel.

Why?

Despite Apple's retooling many system applications (including Finder, Mail, Safari, iCal and iChat) to use 64-bit code, thereby enabling improved performance and access to memory beyond the traditional 4GB, 32-bit limit, most Snow Leopard systems boot into 32-bit mode by default. Defaulting to 32-bit mode helps ensure hardware and driver compatibility.

Not all Intel-powered Macs are even 64-bit capable, it turns out. To learn whether a system possesses 64-bit architecture, click  the Apple menu and select About This Mac. Highlight the Hardware section, then read the entry for the Processor Name. Apple states the following are 64-bit capable:

  • Intel Core 2 Duo
  • Intel Quad-Core Xeon
  • Dual-Core Intel Xeon
  • Quad-Core Intel Xeon

Intel Core Solo and Intel Core Duo systems are restricted to 32-bit use.

All that said, most every important Snow Leopard application runs in 64-bit mode (when run on 64-bit capable systems). Critics complain that iTunes and DVD Player, among other programs, haven't been ported to 64-bit operation. I don't think that's a big deal; I don't see how those apps can benefit greatly from 64-bit processing. In an enterprise environment, I'd much rather have directory services, desktop search functionality, e-mail and Internet browsing running in 64-bit mode.

More important is the fact that, using Snow Leopard, 32-bit and 64-bit applications run simultaneously. Thus, programs that can't be run in 64-bit mode can operate without error, while their 64-bit cousins run faster and smoother thanks to Snow Leopard's 64-bit support.

There's also some misinformation regarding whether Snow Leopard can be forced to boot using 64-bit mode without having to hold down the 6 and 4 keys during startup. The answer is yes; persistent commands can be set.

Enterprise administrators can open a Terminal session and type:

sudo systemsetup -setkernelbootarchitecture x86_64

The setting is then stored in the /Library/Preferences/SystemConfiguration/com.apple.Boot.plist file. Just remember that, with that boot value set, holding down the 3 and 2 keys during startup will override the setting for the specified startup disk and prompt the system to boot using 32-bit mode.

About

Erik Eckel owns and operates two technology companies. As a managing partner with Louisville Geek, he works daily as an IT consultant to assist small businesses in overcoming technology challenges and maximizing IT investments. He is also president o...

3 comments
paulsuma
paulsuma

32bit to 64 bit window server 2003 what iam gona need to do b for upgrading and what problem is gona na happen when i up grade it and what solution should i do for that problem pls help

ian3880
ian3880

being VERY new to a Mac (my partner's actually) after 25 years of PC's I was able to follow the first part and found that her iMac is 64-bit capable (core 2 duo). I've dabbled with Linux and understand command line stuff and the different way Unix stores data, etc. BUT ... For an iMac newbie to ACTUALLY do those changes is ... well ... daunting to say the least. [Not to mention the "recriminations" if I stuff up her iMac big-time :-( ] Is there some way of actually finding out if it is already booting into 64-bit mode, other than assuming it is/isn't?