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Upcoming CPUs from AMD and Apple suggest 64-bit computing will come to a PC near you as soon as this fall.

What does that mean for you? Put it this way: It's not about more megahertz--it's about doubling the amount of data a CPU can process per clock cycle.

A 64-bit PC won't make your word processor run faster, but it can dramatically improve more-demanding applications, resulting in smoother, faster video encoding; better performance on complex programs like CAD; and richer, more detailed games. Over the long term, 64-bit computing will give programmers server-level power and could revolutionize what desktop software can do.

The 64-bit chips (Apple's IBM-made G5 and AMD's Athlon 64) process more data than 32-bit CPUs (Intel's Pentium 4, the Athlon XP, and the Motorola-made G4), and they can address more memory. While 32-bit chips address up to 4GB of physical memory, a 64-bit chip can address up to 16 exabytes of RAM--that's 16 billion gigabytes. (Apple's shipping G5, and high-end Athlon 64 PCs, due this fall, will likely hold a maximum 8GB of RAM, however.)

Though it has the 64-bit Itanium server chip, CPU powerhouse Intel has conspicuously not announced a 64-bit desktop chip. (Unlike AMD's and Apple's chips, Itanium can run 32-bit apps only under slower software emulation.) But there are rumors that Intel has ready a 32- and 64-bit-capable CPU, code-named Yamhill, in case 64-bit desktop computing takes off.

To take advantage of 64-bit chips, you need a 64-bit-capable operating system, apps, and hardware drivers. They won't emerge anytime soon.

Apple's Jaguar and Panther OS upgrades (both due this year) will support 32-bit apps that can make 64-bit requests of the CPU. But a full 64-bit OS has not been announced. Athlon 64 will work like previous Athlons under Windows XP, but its 64-bit abilities will be dormant until Microsoft ships a 64-bit Windows for the chip. That OS, which will support 32-bit apps, is in testing; no word yet on its ship date.

Most software vendors are vague about when their products will offer 64-bit support. Epic Games, maker of the Unreal franchise, is an exception. It has already updated Unreal Tournament 2003 and is awaiting a compatible 64-bit OS, says Tim Sweeney, company founder and lead programmer. In the works is Epic's first fully 64-bit game, due in 2005.

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