Money for Nothing? Rambus Performance Falls Short
by David Essex
Reality Check
For months, we've wondered when Rambus dynamic RAM would begin to demonstrate real-world performance benefits that match its high cost. We're still wondering. Head-to-head against today's standard SDRAM PC memory, it's a tie, at best.
PCs shipping with RDRAM since last fall have quelled some complaints about the pricey new memory by delivering a number of good benchmark results. But it has been hard to tell if other factors, like souped-up 3D graphics boards or faster processors, were responsible for improved performance. 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: RDRAM delivers only a slight performance advantage to some graphics-intensive software but offers virtually none to office applications. RDRAM could come into its own when faster, more demanding CPUs from Intel arrive, and if multitasking of data-intensive software becomes more common. But it must contend with the new Double Data Rate DRAM memory technology.
Things Being Equal
The PC World Test Center custom-built two of the test PCs using Micro Express cases and Intel and Asus motherboards. We also tested two PCs from Dell and four custom units from Micron Technology. All PCs were tested with our PC WorldBench 2000 suite of office applications, 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 this test.
On our Quake III test and MadOnion.com's 3DMark2000 tests, DDR and PC133 SDRAM PCs performed a shade faster in most runs than RDRAM units. But RDRAM consistently nosed out a win on the AutoCAD test. Usually trailing, but not by more than 10 percent, were systems with PC100 SDRAM, probably because they have the slowest memory bus. Save for these PCs, most users would be hard-pressed to notice any differences.
Pros And Cons
Rambus's biggest strength is its high throughput, which lets it pump three times more data per second than PC100 SDRAM. Its alleged weakness is latency, the delay between the time data is requested from memory and when it's delivered to the CPU. Current CPUs, software, and tests tend to exacerbate Rambus's shortcomings and work against its strengths, say memory experts.
Longer latency hampers performance in programs like word processors and certain databases, which tend to jump around a lot making small data requests from memory. It's less of a problem when you're watching DVD movies or editing video, where megabytes of data get blasted out, then stop for a while. RDRAM's greater throughput also comes into play with these types of applications. But as Nathan Brookwood, principal analyst at Insight 64, put it, "The benefit [of Rambus] compared with the pricing is out of line."
Rdram typically adds $150 to $350 to the cost of a preconfigured PC--not an absurd premium, but disproportionate to its slight speed increase. It's on upgrade chips where price differences are stunning. One May posting at Kingston Technology's ValueRAM.com site listed 128MB of the slowest, cheapest RDRAM for $370 more than the fastest non-DDR SDRAM, and 256MB RDRAM modules for $750 more than 256MB of PC133 SDRAM.
Prices should drop as vendors learn to make RDRAM more cheaply. "A year from now, I think a price premium for Rambus in the range of 25 percent compared to SDRAM is very achievable," says Avo Kanadjian, Rambus vice president of worldwide marketing.
What's so great about a premium of only 25 percent?
Enter DDR
Intel archrival AMD favors DDR over RDRAM. Its price premium is better--8 to 10 percent for now, expected to drop to 5 percent when volume production begins, says Semico Research vice president Sherry Garber. And DDR should have less of a latency problem than RDRAM.
But while DDR's maximum throughput is twice that of current SDRAM and competitive with RDRAM, it won't approach that of a forthcoming dual-channel RDRAM. Motherboard design issues related to DDR's wide data bus caused some concern, too.
Bob Eminian, vice president of marketing at Samsung Semiconductor, a manufacturer of all four memory types and the highest-volume RDRAM vendor, dismisses these concerns, saying designers have been working out technical issues for more than two years. "We're forecasting that by the end of next year, Rambus and DDR will hold about the same market share," Eminian says. (The forecast doesn't include DDR SDRAM in graphics boards.) Expect to see AMD Athlon PCs with DDR later this year; the memory is already appearing in high-end servers.
No Case For Now
Kanadjian says people will want RDRAM for playback of downloaded graphics files that will finally show Rambus in its best light. Eminian agrees. He also says RDRAM will show its value when businesses use Windows 2000's improved multitasking to do background data backups, network distribution of large files, and such.
Rambus will also get a boost from Intel's next generation CPU, code-named Willamette. Expected in the second half of this year, the new CPU will require the dual-channel Rambus. When Willamette eventually migrates down to midrange and even low-end PCs, RDRAM will enter the computing mainstream, Brookwood predicts.
RDRAM supporters cite "headroom" when asked why the average person should invest in RDRAM today. But the next-generation 1.5-GHz-and-up CPUs won't work in today's Rambus PCs, and several hundred dollars seems too much to pay for possibilities. Brian Zucker, a technology evangelist at Dell, agrees that as an investment, Rambus probably doesn't make sense for most people, and admits that Dell markets its RDRAM PCs as most appropriate for those with high-end computing requirements now.
Unless you're one of the few whose current apps show substantial gain with RDRAM, wait until the prices come down and software catches up. PC133 SDRAM should suit most of us, providing a minor speed boost on the business applications we typically use, for about the same price as today's PC100 SDRAM. With Intel finally releasing a motherboard that supports PC133 SDRAM, this memory should soon become the mainstream standard. DDR improves performance, but its immediate future is clouded by high cost and uncertain availability.
As for Rambus, no matter how you slice it, most people just don't need it yet.
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