Intel abandons server Rambus efforts

Problems with Carmel frustrate Chipsetzilla efforts

Intel Developer Forum Reliable sources have told The Register that Intel's efforts to implement Rambus technology in its Carmel chipset for standard high volume servers have come to nothing. Carmel is Intel's server Rambus chipset, which can optionally use the Repeater chipset for machines with very large memory arrays. Over the last six months, a team of Intel engineers have attempted to design a Carmel chipset based motherboard for a quad server but that project has now been abandoned. Instead, Chipsetzilla will now use the Reliance chipset for its quad processor, which will use DRAM, instead. As reported here from Computex in June, engineers are doubtful that large arrays of Rambus RIMMs will ever run at 400MHz (800MT/s). Board firms will also have trouble producing reliable boards to run at 400MHz, the sources added. One of the problems is that Rambus technology are microwave circuits and engineers at mobo manufacturers do not have the technical skill to produce such designs. The 354MHz Rambus channels only tipped up on roadmaps over the last three months and specs for the DRCG clock generators use a divider ratio of 8/3. Translated into system terms, the REFCLK frequency of 100MHz generates a Rambus channel frequency of 267MHz, which does not give any performance gains at all. But if the REFCLK input is changed to 133MHz, identical to the front side bus (FSB) frequency, the rabbit pulled out of this piece of Intel magic gives a frequency of 355MHz. This gives a peak channel of 1.42GB/s and there is enough margin to run a reliable Rambus channel by most mobo makers. Sources added that when Intel tested the first prototype Rambus boards earlier this year, they discovered problems due to intersymbol interference and power plane noise. The divide ratio popped out of nowhere shortly after this discovery. No-one at Intel was available to comment on these reports on Saturday night at 8 pm. ®

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