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By | Tony Smith 2nd August 2005 10:03

Elpida samples 4GB FB-DIMMs

Next-gen memory for servers

Elpida has begun sampling 4GB fully-buffered memory modules, a preface to volume production later in the year, the company said today.

The FB-DIMM is pitched at servers, and is based on technology developed by Intel but offered as an open standard. Instead of the usual parallel memory channel bus, in which every DIMM can be 'seen' by the memory controller, there's a two-way, point-to-point serial bus in which the DIMMs are daisy-chained together. Instructions sent to a given DIMM's DDR 2 SDRAM chips to read or write data are stored - buffered - and then forwarded by each DIMM ahead of it in the chain. The memory addresses and the clock timings are buffered too. Data is sent back and forth in packets, co-ordinated by the DIMMs' AMB (Advanced Memory Buffer) chips, eliminating errors and signal interference.

It's also more efficient. A memory controller designed to work with FB-DIMMs needs only 70 circuits to connect to the memory - parallel memory buses need up to 240 lines. And you can add more DIMMs onto the bus: up to six channels are supported, with up to eight DIMMs per channel - 12 times what you'll get on a typical DDR 2 set-up.

Elpida's FB-DIMMs provide data transfer rates of up to 21.2GBps, the memory maker said. Beyond the AMB, the FB-DIMMs use regular, commodity DDR 2 SDRAM chips - in this case, Elpida's 1Gb stacked devices, which yield modules that are 6.7mm thick, much less than the 9.8mm allowed by the JEDEC standard DIMM specification. That, Elpida said, should help air flow more smoothly between modules improving cooling.

Elpida said the modules are available in two performance modes: either PC2-4200F or PC2-5300F. PC2-4200F mode uses 533MHz DDR 2-533 devices with a CAS Latency (CL) of 4-4-4, and the PC2-5300F mode uses 667MHz DDR2 with a CL of 5-5-5. This yields a module data transfer rate of 5.3GBps per channel, 21.2GBps per system in a four-channel configuration.

Both modules are available now for all customers in sample quantities, Elpida said, along with samples of 2GB, 1GB and 512MB capacity FB-DIMMs. Volume production is scheduled for Q4 2005. ®

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