It may be highway robbery, I have no knowledge of what is customary, but it is not a valid excuse for prices to be drastically higher than ddr.
Compared to DDR, RDRAM needs far more expensive ATE
gear with less throughput, much more expensive packaging
(uBGA vs TSOP), and uses a more area inefficient multibank
scheme. Add to that RDRAM's lower yields from much more
complicated and finicky mixed signal circuitry for signalling
and clocking and it's no wonder it cost far more than DDR.
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