Richard, regarding this quote:
A DDR SDRAM chip operating at 133 clock/266 dr has a bandwidth of 266mb/s/pin. A DRDRAM chip operating at 400 clock/800 dr has a bwandidth of 800mb/s/pin. Consider in most cases both of these chips are 16(or 18 in the case of rambus) wide, then for a given chip, rambus is much much faster.
It's a little more complicated than that. I'm sure Carl would love to take issue with this quote, but since he hasn't responded yet (hope he wasn't scared away by us pro-Rambus nuts), I'll go ahead.
DDR does indeed have a bandwidth of 266 Mbit/sec/pin, while RDRAM has a bandwidth of 800 Mbit/sec/pin. However, RDRAM does need more supporting pins, especially power and ground, because of the higher clock speeds. So the pincount advantage isn't as great as the bandwidth-per-pin numbers would suggest, but at least there's still an advantage.
The second statement, however, is kind of an apples-to-oranges comparison. All RDRAM chips are 16 or 18 bits wide (depending on whether ECC is desired). But DDR chips come in different sizes, like 8/9-bit (I think), or 16/18-bit, or 32/36-bit. The difference, however, is that with DDR, you always need a 64-bit channel, so with 8-bit chips, you have to gang eight DDR chips together. With 32-bit chips, you only need two, but the net sum has to be 64 bits. RDRAM, however, only requires at least one chip. The additional chips are attached in series, not in parallel, and their purpose is only to increase capacity. Are you following me here?
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