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64-bit desktop computing has taken a significant step toward becoming a pervasive reality: AMD's release of its Athlon 64 chips--and Apple's launch of its G5 CPUs--means 64-bit processors, once reserved for servers and high-end workstations, are now in PCs available on retail shelves.

In time, 64-bit PCs could change the face of desktop computing. A 64-bit chip can run longer, more complex instructions than a 32-bit one, improving performance of data-intensive tasks such as audio and video encoding, advanced engineering design apps, and, naturally, games.

Equally key is a 64-bit CPU's ability to recognize and use a lot more RAM. Today's 32-bit chips, such as AMD's Athlon XP and Intel's Pentium 4, can address up to 4GB of RAM split between the OS and applications. Few PCs have that much memory, and even fewer apps use it. But with ever-more-complex software, that limitation may become a bottleneck, making Athlon 64's ability to address a whopping terabyte (1000GB) of physical memory very attractive.

But you will need a 64-bit-capable operating system, new hardware drivers, and 64-bit applications to fully take advantage of such a chip, and therein lies the rub.

A few Linux distributions, including Red Hat and SuSE, already offer (or will soon) 64-bit editions for Athlon 64s, but Microsoft's 64-bit Windows XP for these chips won't ship until early 2004--and even it won't offer most users what they really need (see "Sneak Peek"). Aside from a handful of expected programs, such as DivXNetworks' DivX video encoder, 64-bit desktop software will be an even longer wait. The lack of full support is one reason Intel has no current plans to introduce a 64-bit desktop chip (see "Why 64-Bit Now?" for more on Intel's views).

AMD knew 64-bit desktop computing wouldn't be ready for prime time right away, so it made its 64-bit Athlons hybrid CPUs that can also run today's 32-bit apps. And our initial tests show the chips run them very well (see the chart).

Apple's latest OS X has 64-bit extensions, providing the new Mac G5s and a few optimized apps a taste of greater power. But that isn't quite enough to give Apple a wholesale performance edge. (For more on Apple's 64-bit platform, and its G5's performance versus Athlon 64 PCs, see "64-Bit Computing According to Apple.")