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Intel's 64-bit Pentium 4 and Pentium 4 Extreme Edition desktop processors launched in February, giving the 64-bit computing future that started with AMD's Athlon 64 chips even more traction.

What does 64-bit computing offer you beyond today's 32-bit platform? We compared two of the new chips, the 3.73-GHz P4 EE and the 3.6-GHz P4 660, with a 32-bit 3.8-GHz P4 (the fastest 32-bit P4), a 2.6-GHz Athlon 64 FX-55, and a 2.4-GHz Athlon 64 3800+. Results are mixed: You'll get a slight boost over a 32-bit P4, but you will pay about $100 to $200 more for an Intel PC than for an AMD one with similar or slightly better performance.

Intel also has implemented its 64-bit extensions on P4 chips at 3 GHz to 3.4 GHz, and will do so on forthcoming P4 and Celeron CPUs. The new P4s also get a boost in their on-board L2 memory cache from 1MB to 2MB. You won't need a new motherboard for the new chips, but to get the most out of their 64-bit capabilities, you will need to upgrade your BIOS and, of course, run a 64-bit operating system. Microsoft's 64-bit Windows XP Professional X64 should be generally available in late April; it will run on PCs using both Intel's and AMD's 64-bit chips (for a preview of 64-bit Windows, see "XP Goes to 64 Bits" in the March issue). Systems with 64-bit P4 and P4 EE CPUs are already on sale.

One other chip is entering the desktop fray: Intel's Pentium M, originally designed for mobile PCs. We take a look at one of the first desktops to use this CPU in "New Desktops: Pentium M Inside."

Close Race

We tested the 64-bit processors with both 32-bit Windows XP Professional and Release Candidate 2 of Windows XP Pro X64; the 32-bit P4 was tested only with standard Windows XP Pro. We used different motherboards for the AMD and Intel platforms in our test PCs but used the same 160GB Seagate hard disk and NVidia GeForce 6800 graphics card with 256MB of RAM. The Intel test systems used 1GB of 533-MHz DDR2 memory, while the AMD ones had 1GB of DDR400 RAM.

The Athlon 64 3800+ and the 3.6-GHz Pentium 4 scored so close to one another on WorldBench 5 under 32-bit Windows that users wouldn't notice a difference (see chart). The gap was slightly more noticeable between the Athlon 64 FX-55 and the P4 EE, but still under 10 percent. Note, though, that only about two-thirds of WorldBench 5 apps run on XP X64--and in many cases (not shown in the chart), both AMD's and Intel's CPUs lost ground with the 64-bit OS--so it's difficult to predict what the final total would have been. The 32-bit and 64-bit P4 CPUs performed essentially the same on WorldBench 5.

However, the 64-bit P4 did show a slight performance increase over the 32-bit P4 in Unreal Tournament with a 32-bit operating system at the lowest resolution we tested (1024 by 768). Test scores using AMD's and Intel's 64-bit processors showed mild drops with Unreal Tournament going from a 32-bit OS to a 64-bit one. Still, everything else being equal, we're convinced that you'll lose little or nothing with Intel's 64-bit extensions.

Pros and Cons of Running at 64

Until XP Pro X64 ships, most users--save those running Linux, which can already take advantage of 64-bit CPUs--won't derive any benefits from 64-bit computing. Even when the operating system ships, only applications optimized and recompiled to take advantage of the new capabilities will deliver any performance increase. Note also that the main boon of 64 bits is the ability to handle larger amounts of data and at higher resolutions, not speed. That means a 64-bit PC will be able to juggle far larger databases and spreadsheets, a lot more on-board memory (up to 64GB with Intel's 64-bit solution and 1 terabyte with AMD's version), and higher resolution in games, audio, and video, but it will not give huge performance boosts.

A couple of other caveats before you jump the 32-bit ship: 32-bit drivers don't work with Windows XP Pro X64, and vendor support for older hardware will probably be skimpy. Companies are reluctant to spend money updating drivers for products they no longer sell. If you want to hold on to older hardware, you might have better luck with 64-bit Linux since there's often someone, somewhere who will take the time to write drivers for legacy equipment.

And productivity software vendors won't be stampeding to port their apps to 64-bit Windows for quite some time. A number of 64-bit games are on the way, along with several audio and video apps. Cakewalk's Sonar X64, a 64-bit high-end audio recording app, is already available as a trial version from the company's Web site, but few other 64-bit programs have yet appeared.

One Chip, Two Cores

Desktops will get another boost from dual-core CPUs, which are expected to arrive in the second half of this year. Many vendors already offer Pentium or Athlon systems that can use two or more processors, but dual-core CPUs will share the same piece of silicon instead of just the same motherboard. This neatly improves multitasking performance without increasing clock speed--something Intel's been having problems with on the Pentium 4. Better multitasking helps in a number of scenarios. For instance, one of the cores could focus on burning a DVD while the other recalculated a spreadsheet or performed a database search. Just don't expect huge speed gains while working in today's single applications unless they perform simultaneous tasks, as the multithreaded Adobe Photoshop does.

Intel announced its new dual-core Pentium Extreme Edition 840 and Pentium D processors in March, and demonstrated working dual-core machines from Dell and others (none are yet available for testing). Unlike with the new 64-bit chips, you can't plug the dual-core CPUs into current systems because, while they use Intel's current LGA775 socket, they require motherboards using yet-to-be-released 955X or 945 chip sets. AMD showed a dual-core Opteron server at LinuxWorld in late February, and plans to ship its desktop dual-core Toledo Athlon 64 CPUs later this year. The Toledo will require only minor tweaks to your BIOS, not a new motherboard, and it plugs in to current Athlon 64 sockets.

Dual-core CPUs hold a lot of promise for users who juggle multiple tasks, but AMD, for one, has indicated that high-speed single-core chips will remain the top performers at least until year's end.

If you're in the market for a fast system today with some hooks into tomorrow's 64-bit world, either an AMD-based or Intel-based 64-bit model will serve. Intel PCs are a bit slower and pricier than comparable AMD ones, but the performance gap is slim, so Intel fans won't lose much.