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To: Sun Tzu who wrote (73977)5/31/2001 2:35:31 PM
From: Bilow  Read Replies (1) | Respond to of 93625
 
Hi Sun Tzu; Re: "So you are both agreeing that one cannot fit enough RDRAM in a server. At least not the kind of server that IA-64 was made for. Yet somehow Intel saw fit to make McKinley RDRAM compatible?! Why?"

Intel made a mistake.

They assumed that RDRAM would be the next mainstream memory, and that it would provide the highest memory per chip. In fact, the memory industry didn't increase bits per chip (i.e. density) as fast as what had been predicted, and in addition, RDRAM prices never dropped to SDRAM levels. In addition, at any given density, SDRAM chips became available long before the same size RDRAM chips. This means that at any given time, SDRAM provides higher densities. In addition to the higher densities per chip, SDRAM provides higher densities per module, and more modules per channel:

RDRAM, 512MB/RIMM, mass production at Samsung:
samsungelectronics.com

SDRAM, 1GB/DIMM, mass production at Samsung:
samsungelectronics.com

SDRAM can have 4 DIMMs, while RDRAM can only have 2 RIMMs. Result: Maximum memory per channel is 4GB for SDRAM, and 1GB for RDRAM. You can repeat RDRAM channels (and SDRAM channels also), but that adds latency, cost, risk and board space. The upshot is that even at Samsung, Rambus' biggest supporter, SDRAM has a 4x density advantage over RDRAM.

-- Carl



To: Sun Tzu who wrote (73977)5/31/2001 3:35:44 PM
From: Dave B  Respond to of 93625
 
ST,

Yet somehow Intel saw fit to make McKinley RDRAM compatible?! Why? It seems to me that based on what I've read here, DDR is a much better choice for McKinley.

Don't know. Maybe the Register story is wrong (it's happened before <G>).

Dave