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Technology Stocks : Rambus (RMBS) - Eagle or Penguin -- Ignore unavailable to you. Want to Upgrade?

To: richard surckla who wrote (33825)	11/4/1999 1:12:00 PM
From: Tenchusatsu	Read Replies (2) \| Respond to of 93625

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? Tenchusatsu

To: richard surckla who wrote (33825)	11/6/1999 10:55:00 AM
From: Dan3	Read Replies (1) \| Respond to of 93625

Re: for a given chip, rambus is much much... DRAM chips by themselves are never used for PC memory. Memory used in one or two chip applications is migrating towards embedded DRAM (like nintendo going from Rambus to embedded). Speed of memory can be measured several ways, the most common are latency and bandwidth. The bandwidth is determined by the bandwidth per bus and the number of busses or "channels". Rambus 800 has a per bus rate of 1.6Gb/sec, DDR 266 has a per bus rate of 2.1 Gb/sec. DDR also has lower latency and lower cost. Dual Rambus busses still have longer (worse) latency times but by combining two busses in parallel, bandwidth goes to 3.2 Gb/sec - but cost and density, already a rambus disadvantage, have now risen considerably. DDR 333 is being used in some video applications now and will have a bandwidth of 3.3 Gb/sec in a single PC "channel". Think of it this way: Rambus is 16 bit memory while SDRAM, DDR, etc., are all 64 bit DRAM. Rambus has to work very hard to get (64 bit wide) DDR levels of bandwidth out of its 16 bits. If a rambus channel runs 4 times as fast as a conventional channel, bandwidth is equal. Because of the delays due to parallel to serial conversion, (rambus is 128 bits wide internally) rambus always has longer latency. Regards, Dan