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For months, we've wondered when Rambus dynamic RAM would begin to demonstrate real-world performance benefits. We're still wondering. Head-to-head against today's standard SDRAM PC memory, it's a wash, at best.

RDRAM PCs that have been shipping since last fall seem to do better on some benchmark tests, but it is difficult to tell if other factors--like faster CPUs or souped-up 3D graphics boards--are responsible for performance improvements. To clear the air, we isolated the effects of RDRAM by testing identically configured 800-MHz PCs that use either RDRAM or SDRAM technologies.

The upshot, at least for now, is RDRAM delivers only a slight performance advantage to some graphics-intensive software, such as high-end design or multimedia authoring apps, and virtually none to office applications. RDRAM could come into its own as faster, more demanding CPUs from Intel arrive, and if multitasking of data-intensive software becomes more common. But it is no longer alone in the vanguard of memory technology. A new type of memory called Double Data Rate SDRAM looks like a contender.

Untangling Acronyms

First, let's translate the alphabet soup. SDRAM is Synchronous DRAM, the workhorse of modern PCs. PC-100 SDRAM refers to SDRAM running at 100-MHz bus speed; PC-133 SDRAM runs at 133-MHz bus speed.

RDRAM is Rambus DRAM, a new type of memory that can run about three times faster than typical SDRAM. The current version supports bus speeds between 600 and 800 MHz, which is why RDRAM is often identified as PC600, PC700, or PC800.

DDR SDRAM refers to Double Data Rate SDRAM, an upcoming system RAM technology. It borrows a technique from RDRAM to double SDRAM's data-transfer rate to roughly RDRAM speeds.

Level the Playing Field

The PC World Test Center asked PC vendors to configure Intel Pentium III PCs, changing only the memory type. We tested two PCs from Dell, four systems built for us by Micron Technologies, and two PCs we assembled ourselves using Micro Express cases and Intel and Asus motherboards. We then ran our PC WorldBench 2000 suite of office apps, graphics programs, and more.

A Dell Dimension PC using RDRAM on a 700-MHz bus between CPU and memory (called PC700) scored 151 on PC WorldBench 2000, just a point higher than a fellow Dell with 100-MHz (PC100) SDRAM. The four Microns, representing RDRAM, DDR SDRAM, PC100 SDRAM, and the new 133-MHz (PC133) SDRAM, also showed negligible differences on PC WorldBench 2000.

On our Quake III test and MadOnion.com's 3DMark 2000 tests, DDR and PC133 SDRAM systems performed a shade faster in most runs than RDRAM PCs. But RDRAM turned things around on the AutoCAD test, consistently nosing out a win. Usually trailing, but never by more than 10 percent, were PCs with PC100 SDRAM, probably because they have the slowest memory bus. Save for these systems, most users would be hard-pressed to notice any of the differences.