64-Bit Takes Off

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The Score

We tested three systems using the high-end 2.2-GHz Athlon 64 FX-51 chip with dual-channel memory, and a PC with the more mainstream Athlon 64 3200+, which runs at 2 GHz and has single-channel memory. We also looked at an identically configured 3.2-GHz P4 PC for comparison. All PCs had 1GB of DDR400 memory and an ATI Radeon 9800 Pro graphics card. All tests were performed with 32-bit software.

The three Athlon 64 FX-51-based units--from Alienware ($3535), Falcon Northwest ($3245), and Voodoo ($3250)--notched an average PC WorldBench 4 score of 142, the fastest we've seen. ABS' Athlon 64 3200+ PC ($1924) scored 139; Alienware's P4 comparison unit ($3143) earned 126. The scores for three previously tested 32-bit Athlon XP 3200+ PCs averaged 136; seven previously tested 3.2-GHz P4 units earned an average of 127. (Prices above exclude a monitor and speakers.)

Systems with the FX-51 showed pronounced improvements in some of our more CPU-intensive tests, particularly AutoCAD, where they were about 44 percent faster, on average, than the P4 unit. The FX-51 PCs also stood out on our Premiere tests, and posted top scores on the Photoshop and VideoWave tests. The P4-based PC had the best score in our Musicmatch test.

In our game tests, again the FX-51 PCs were clear winners, posting noticeably higher scores. (Note: Lower resolutions show CPU power better than higher ones because the graphics subsystem contributes more at high res.)

Memory Boost

Besides adding 64-bit capabilities, AMD made other improvements to its new CPUs. They include a 1MB L2 cache (up from 512KB), a faster system bus based on HyperTransport technology (up to 1600 MHz), and new SSE 2 instructions. But probably the most important change was the move to an on-chip memory controller.

Typically the memory controller resides on the motherboard as part of the chip set, connected to the CPU via the frontside bus. Athlon XP has a maximum frontside bus speed of 400 MHz; Intel's latest P4s offer 800 MHz. By integrating the memory controller, AMD gives memory a private channel to the CPU: It no longer has to share a pipe with other components and needs no middleman to process its request. Unlike CPU cache, the integrated memory controller runs at the memory speed, not CPU speed.

"The on-board memory controller provides more bandwidth and drops the latency," says Kevin Krewell, general manager at research firm MicroDesign Resources. Lower latency means less time between the CPU asking for data from RAM and getting it.

Two Athlons

AMD's new chips also have real architectural differences between them. For example, the FX-51's dual channels can move up to 6.4GB of data per second with DDR400 while the mainstream Athlon 64's single-channel DDR can move up to 3.2 GBps. More: The FX-51 requires a 940-pin socket (the Athlon 64 3200+ uses the new Socket 754), and more expensive registered-memory DIMMs. Usually reserved for servers, a registered DIMM includes an internal buffer that allows more memory chips per DIMM, but with a delay of half a clock cycle required to help prevent errors. The FX-51 is also easier to overclock than the Athlon 64, although AMD won't officially recommend doing that (it still voids the warranty).

AMD charges vendors $733 for each FX-51 in lots of 1000, versus $417 for the Athlon 64 3200+. (The 3.2-GHz P4 is $637.) That's a hearty premium for the FX-51, but it's a price that performance buffs are likely to pay, says Dean McCarron, principal analyst with Mercury Research.

There should be little confusion between AMD's two new chips, but you'll note the company gave the 2-GHz Athlon 64 the same 3200+ performance rating as that of its last 32-bit Athlon XP chip (FX-designated chips dropped the performance ratings altogether). Check before you buy: AMD will sell both 3200+ CPUs for the near future.

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