Athlon's 64-bit question.

Inside the Internet.
Oct. 24 2003 10:49 AM

The 64-Bit Question

AMD has built the world's fastest PC. Should you buy one?

For status-conscious PC owners, it's time to toss the Pentium. A new 64-bit Athlon CPU from AMD was dubbed the "fastest ever" last month by PC World magazine. Racing a few AMD-equipped computers against Intel's latest Pentium 4 models, the magazine deemed the Athlon 64s a good 10 percent faster overall.

AMD, long a distant second to Intel in the microprocessor business, is gunning for more than the pure speed crown. The company claims its 64-bit chip will launch a new era of "cinematic computing," the term used by makers of graphics cards to suggest computer animation so rich it looks like video. But boilerplate hyperbole doesn't answer the basic questions: What exactly is a 64-bit CPU? More important, should you buy one?

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First, the 64-bit question. A CPU is the computer's central processing unit (you probably knew that), where most of the computing gets done. Sixty-four bits is the measure of the chip's word length, the maximum number of bits (the basic 1's and 0's of digital data) that will fit into each of the chip's internal registers. (Registers are where programming instructions and incoming data are placed in order to perform calculations with them.)

Current CPUs for PCs have eight registers that hold 32 bits each, which imposes two limits on them. First, they can't access more than 4 gigabytes of RAM. That's because each byte (a byte is eight bits, treated as one chunk of data) of RAM has a unique address number that needs to fit into one register. Since each bit has at most two possible values—0 or 1—a 32-bit PC can handle 232 addresses,which multiplies out to 4 gigabytes of RAM. Upgrading to 64-bit registers lets the chip access 264 bytes—that's 18 billion gigabytes, more RAM than exists on the entire planet.

Second, on a 32-bit machine, numbers that run longer than 32 bits (for example, fussy values of pi) require lots of juggling in order to perform calculations. That slows down computer-aided engineering and animation, corporate data mining, and other number-crunching applications. It adds bugs, too, as these overlong numbers are shuffled among registers. Upping the register size to 64 bits is like widening the freeway, which is why high-end servers and professional graphics workstations moved to 64-bit processors years ago.

On our desktops, though, most of us haven't had a pressing need for the upgrade. A 64-bit CPU won't make Microsoft Office run any faster, and it doesn't speed up e-mail or Web surfing. It won't help anyone this side of Warren Buffett with the family spreadsheets. That's why Intel decided not to develop a 64-bit Pentium, putting its efforts instead into a 64-bit chip called Itanium meant to run specialized applications in corporate backrooms rather than consumer software on home PCs.

AMD is pushing the 64-bit label in hopes that, like Microsoft shrugging off the Internet fad a decade ago, Intel has woefully misjudged the demands of its customers. There's also the hope that computer buyers will treat 64-bit computers like they do computers with more gigahertz—they don't know what it is, but they assume that more is better.

But right now, there are only two obvious uses for a 64-bit PC at home: games and video. For video, doubling the CPU's word size means the billions of bits in a movie can be encoded and decoded more efficiently, enabling higher resolutions and faster editing.

Games work differently. A separate graphics chip renders the videolike images, while the CPU usually calculates the behavior, position, and motion of each object in the game—whether it's the physics of a bouncing ball or the sneaky moves of a robot adversary. Game programmers say the problem with Pentiums isn't that they have 32-bit registers, but that they have only eight of them. The new Athlon tackles that, too, sporting 16 double-wide registers. Rebuilt 64-bit editions of games will be able to use those extra registers to calculate more realistic motion and faster-thinking opponents.

So, the buyer's guide is easy. If you absolutely must get a new PC now and want the fastest available, AMD has the season's hot chip. Keep in mind, however, that its raw speed has nothing to do with the fact that its word length is 64 bits. The era of "cinematic computing" won't kick in until there's software written for the chip's 64-bit capabilities and its extra set of registers. If you have to buy a PC now, you might as well buy a 64-bit one, so you're not disappointed when Microsoft (which owns Slate) puts out its 64-bit Windows XP sometime next year, or when the game-makers flood next year's holiday shopping season with 64-bit titles.