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Previously, if you wanted Intel's Pentium 4, you had to buy a PC with pricey RDRAM. But now Intel has released its PC-133 SDRAM-based chip set, the 845, and Via Technologies has launched its unlicensed chip set, the P4X266, which pairs the P4 with DDR memory. So which offers you the best combination of value and performance?

Each memory type has its proponents. Cost-conscious upgraders and IT groups want an SDRAM chip set for the P4 because SDRAM is an inexpensive and trusted memory type. DDR--formally, DDR SDRAM--is also fairly cheap and promises better performance, which excites some PC enthusiasts. Intel, RDRAM's strongest advocate, contends that RDRAM-based PCs offer the very highest performance.

The Tests

In exclusive PC World tests comparing three similar 1.7-GHz P4 PCs--each carrying 256MB of SDRAM, DDR, or RDRAM and running Windows 2000 Professional--the RDRAM-based system outran the PC-133 SDRAM-based PC as expected, though by fairly small margins. But the comparable DDR-based PC outpaced both systems on most of our tests, including a multimedia task--an area where we had expected the RDRAM system to shine. And despite the recent plunge in memory prices (see "More Memory, Please"), RDRAM remains roughly three and four times costlier than DDR and SDRAM, respectively.

We asked Dell Computer to supply us with two matching P4 systems: one based on Intel's RDRAM chip set, and the other on Intel's SDRAM chip set. Shipping systems configured with a P4 CPU and DDR memory weren't available at test time, so we requested a reference system from Via.

Dell sent us a shipping Dimension 8100 with 800-MHz RDRAM and a preproduction Dimension 4300 with 133-MHz SDRAM. Both units carried identical 60GB, 7200-rpm IBM hard drives; NVidia GeForce3 graphics cards with 64MB of DDR SDRAM; 16X DVD-ROM drives; 16X/10X/40X CD-RW drives; and 17-inch monitors.

Via's system came with 266-MHz DDR memory; a 40GB, 7200-rpm IBM hard drive; an NVidia GeForce2 Pro graphics card with 64MB of DDR SDRAM; a 12X DVD-ROM drive; and a 17-inch monitor. (Note that our tests emphasized 2D over 3D graphics, and the graphics cards in each system were deemed sufficiently comparable to permit accurate testing.)

The DDR-based system led the pack with a PC WorldBench 2000 score of 230; the RDRAM PC landed a 219; and the SDRAM unit a 208. That gives the DDR PC about a 5 percent lead over the RDRAM system, and a 10 percent advantage over the SDRAM unit. The RDRAM unit bested the SDRAM system by slightly more than 5 percent.

In our timed MusicMatch test, the three systems finished within 2 seconds of one another, with the DDR-based unit managing a tiny lead. Scores were also close in our Photoshop 5.5 test: The DDR- and RDRAM-based systems finished in a tie, each of them completing the test nearly 5 percent ahead of the SDRAM unit; that's a difference you might notice over a workday.

The DDR-based system really showed its stuff in the timed AutoCAD 2000 test, which it completed in 7 minutes, 18 seconds. In contrast, the RDRAM-based PC took 9 minutes, 1 second and the SDRAM-based unit took 10 minutes, 14 seconds. The DDR unit thus ran 23 percent faster than the RDRAM PC, and a whopping 40 percent faster than the SDRAM unit. You're unlikely to miss that. In addition, you'd probably notice the 13 percent speed difference between the RDRAM and SDRAM machines.