Why Intel's Foster will use DDR memory

At last, some Rambus clarification

When Intel announced its up-and-coming Willamette processor at last month's Developer Forum, many were puzzled as to why the company said that the server version of the 1.4GHz processor, codenamed Foster, would use double date rate (DDR) memory rather than the Rambus memory recommended for its desktop chip. Now, at last, there is clarification on the topic, from a savvy reader, as well as a leading industry analyst. According to Nathan Brookwood, principal analyst at Insight 64 in the US, the reason that server vendors have avoided Rambus memory is that they use lots of DRAM in these systems, and would end up paying between four to six times the cost per megabyte if they use RDRAM. Also, he adds, the ServerWork (formerly Reliance) chipsets support a 128-bit wide memory system, so they get more than enough memory bandwidth (~2.1GB/second) using "plain old" PC133 SDRAM. At the same time, Brookwood clarified market share projections for Rambus chips, following our story yesterday. He said: "The most aggressive RDRAM forecasts for this year call for ~120M chips, enough for ~15M RIMMs. Since a typical high-end PC has slightly more than 128MB of memory, this translates into 10-12M PC's, which is consistent with the positioning of Rambus-based systems in the performance and/or enthusiast segments." Dataquest forecasting 200 million Rambus chips (not RIMMs) for this year, a figure that is probably far too optimistic. Semico, another chip market research firm, is projecting output of 80 million units. A reader adds: "Intel is expecting that desktops with the Willamette processor will be running with 128MB PC700 RIMMs. This configuration does OK for speed, although the memory will lag severely behind the processor. "Rambus memory, however, because of its internal serial packet design, slows with each memory chip added to the configuration, with a noticeable change occurring with each new RIMM. With a typical server specification including 1G+ of RAM, the Rambus protocol design slows to the point that even current single data rate memory is faster. He adds that if you expect to use a lot of memory in a system, Rambus is far from ideal. "Intel expects desktops to stay in the low memory range so Rambus is fine. An eight way processor system with 8GB of memory is only possible if Rambus is kept out of the box (assuming Gigahertz speeds)." ®

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