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.

By Erik Eckel

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...