So, we needed Registered DDR SDRAM modules. Right now there are a lot of Registered DDR400 modules in the market with different capacities. For our tests we used HyperX memory modules from Kingston.
These memory kits with the KRX3200AK2/1G part number consist of a pair of 184-pin Registered DDR400 DIMM modules supporting ECC. Each kit is 1GB big, i.e. it consists of two 512MB modules. The nominal frequency this memory works at is 400MHz and the voltage is 2.6V. This memory can work with 2.5-3-3-6 timing settings. At least this is what the specification claims. The SPD of these memory modules contains slightly different info: the timing settings listed there are a little bit less aggressive: 3-3-3-8.
During our practical tests we managed to prove that Kingston HyperX KRX3200AK2/1G memory modules work stably and reliably at 2.5-3-3-6 timing settings that is why all our dual-Opteron workstation testing will be carried out with these particular timings.
Note that although these timing settings of 2.5-3-3-6 could look very poor for the regular unbuffered DDR400 SDRAM, they are pretty typical for the today’s registered memory solutions. It is very hard to find Registered memory with more aggressive timing settings today. So, I don’t think anybody will accuse us of having made the wrong choice on the memory for our workstation.
During our workstation tests we installed two sets of Kingston HyperX KRX3200AK2/1G memory, i.e. the total of 4 modules, 512MB each. So the overall memory capacity on our platform was 2GB.
The system memory was distributed between the two CPUs evenly: two memory modules were installed into the DIMM slots assigned to the first CPU, and the other two – into the DIMM slots of the second CPU. This configuration allowed us to use the symmetric implementation of the NUMA technology. So, our workstation had four independent DDR400 SDRAM channels, which provided 12.8GB/s theoretical peak bandwidth of the memory subsystem.