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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: Joe NYC who wrote (96679)	3/4/2000 1:59:00 AM
From: Tenchusatsu	Read Replies (1) \| Respond to of 1574683

Joe, technical reasons behind RDRAM and DDR SDRAM positioning: RDRAM + Low number of pins: Excellent for chipsets, less expensive north bridge design, also excellent for having two or four RDRAM controllers in parallel + Finer granularity: As memory density increases, fewer chips can be used. + Smaller packaging: (Or so I'm told; I can't be sure.) + Efficient in bandwidth utilization. + Great for systems which don't need high capacities (gigabytes) of memory. - High prices: Hopefully, this should come down as RIMM production ramps up. - Huge transition hump from SDRAM to RDRAM production. - Lower max bandwidth compared to DDR, but efficiency makes up for it. - Slightly longer latency: For desktops, this can have a noticeable impact on performance, though I believe the chipset makes a much bigger difference on latency than RDRAM itself. DDR SDRAM + Higher capacity limit per channel: RDRAM only allows for 32 chips per channel, but with double-sided, double-stacked DIMMs, SDRAM allows for 128 chips per channel. This leads to 4x the max capacity. + New density technologies (256 Mbit coming up, 512 Mbit after that) will probably show up on SDRAM before RDRAM. + Easier to implement ECC and chipkill features than on RDRAM. That's critical for high RAS in servers. + Higher max bandwidth than RDRAM. + Slightly lower latency than RDRAM. + Likely cheaper to manufacture. - Pin count requirements are significant. I think it's 2 to 3 times that of RDRAM. - Because of pin count, it's harder to group two or more DDR channels in parallel. - Possible electrical concerns: Despite the difficulties implementing RDRAM, implementing DDR isn't going to be easy. - Coarser granularity than RDRAM. You can have fewer than eight chips on a DIMM, but the packaging will be larger and more expensive per chip. - Less efficient at utilizing bandwidth, which negates DDR's max bandwidth advantage over RDRAM. Those are the technical reasons off the top of my head, based on the opinions of me and my coworkers. As usual, they're subject to change based on Intel's "official" positioning. But for the most part, I think Intel will continue to back RDRAM in the future, except in servers where the higher RAS and capacity of DDR is critical. Tenchusatsu