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NOVEMBER 7, 2003
By Stephen H. Wildstrom What's the Story with 64-Bit Chips? Wondering what all the buzz is about -- and whether you need one of these speedsters now? Here are some answers If you pay attention to what's happening in personal computing, you're going to be hearing quite a bit in coming months about 64-bit processors. Apple (AAPL ) has made a splash with its PowerMac G5 desktop, based on a new 64-bit G5 processor, while desktops built around Advanced Micro Devices' (AMD ) 64-bit Athlon 64 chip have just started shipping. So, what is a 64-bit processor? What can it do for you? And when will you need one? Nearly all of the processors used in desktops and laptops today take in data and programming instructions in 32-bit chunks, as they have for most of the last 20 years. Doubling the size of those chunks could, in theory, make computers faster. But system speed is the result of many different factors, and there's no guarantee that a 64-bit chip will be faster that a 32-bit one in real-world applications. WHOLE LOT OF MEMORY. Mainframes and other heavy-duty computers, especially those from IBM (IBM ) and Sun Microsystems (SUNW ), switched to 64-bit processors a long time ago to meet an entirely different need. A 32-bit processor can handle only 4 gigabytes of memory. Four billion bytes is a lot of memory, about 16 times as much as is in most laptops and desktops, but it's not enough for computers that run really large databases, such as those used by banks to manage transactions. A 64-bit processor can use 18 exabytes -- that's 18 billion billion bytes -- of memory, orders of magnitude greater than any physical computer could actually hold. (Don't even think about 128-bit chips. Not enough silicon atoms are probably on earth to build that much memory.) So why even bother with 64-bit chips on desktops? Both Apple and AMD are making a virtue of necessity. In Apple's case, the old G4 processor (which its maker, Motorola (MOT ), calls the PowerPC 750) had run out of growing room, and Apple desperately needed something faster for its high-end PCs. And for reasons of cost, it needed to use an existing design as a starting point. FILLING A GAP. IBM, which had partnered with Apple and Motorola in the original PowerPC design, had developed a very speedy 64-bit PowerPC derivative for its big servers called the Power 4. Apple worked with IBM Microelectronics to modify the Power 4 for use in Macs, and the result is what Apple calls the G5, and IBM calls the PowerPC 970. AMD's route to 64 bits was totally different. Intel (INTC ) had left a strategic gap in its lineup of server chips between its fastest Xeon models, which are based on 32-bit Pentium technology, and its 64-bit Itanium processor, a totally new design that requires that existing software be rewritten to run efficiently. AMD came up with a 64-bit chip, code-named Hammer, that uses the same instructions as the Pentium. The server version of Hammer is called Opteron, and AMD decided that since its 64-bit chip would run existing 32-bit programs at least as fast as any Intel chip, it would develop a desktop version. That's the Athlon 64. Both the G5 and the Athlon 64 have some drawbacks. For the G5, it's that the chip doesn't just sizzle in performance. It also generates prodigious amounts of heat that preclude it from being used in anything but big desktop boxes. It will probably be at least a year before IBM builds a more advanced version that can run in compact iMacs or in laptops. UNNECESSARY PROGRESS? AMD's problems are more serious: Hardly any software exists that lets the Athlon 64 perform at its best. AMD's chip can operate in three modes. They might be described as fast, faster, and fastest: a 32-bit operating system with 32-bit applications, a 64-bit operating system with 32-bit applications, and pure 64-bit. Only the first is really available today, at least for Windows, because Microsoft has issued only a test version of 64-bit Windows XP for Athlon. For the time being, the Athlon 64 mostly makes for a very fast 32-bit machine, which is why the top-tier computer makers aren't yet offering Athlon 64 products. Intel argues that 64-bit processors on desktops are at best premature and at worst completely unnecessary. It claims, with some justification, that the 4-gigabyte memory ceiling isn't meaningful to desktop users (a few very high-end Apple customers who work with enormous media files might disagree). And Intel plans to stay ahead in the raw-speed race with a new version of the Pentium 4, code named Prescott, set to debut before yearend. The bottom line is that the server world is migrating toward 64-bit computing, at least from the midrange on up. But you have no reason to believe you're missing anything if the processor in your desktop or laptop is a measly 32-bit model. That's likely to remain the standard for some time to come.  Wildstrom is Technology & You columnist for BusinessWeek. Follow his Flash Product Reviews, only on BusinessWeek Online
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