Intel 7400 Memory Population

Intel’s The Server Room blog has an interesting tidbit of information for those of us thinking about servers with the Intel 7400 series of CPUs in it:

As mentioned before, an MP Xeon 7400 series server will provide four channels of FBD memory. There are a couple of considerations here. First, latency to memory increases for every DIMM added to the system. This is important to note because you can keep the memory latency to a minimum by adding fewer high capacity DIMMs. Second, be sure to evenly distribute the DIMMs across all the channels. In other words, don’t fill up all the slots on one channel and then lightly populate the rest.

Some systems get faster when you have more DIMMs, some get slower, and it’s information like this that can sometimes push us from sixteen 2 GB DIMMs to eight 4 GB DIMMs. On the other hand, there’s always the price. A DIMM that has double the capacity often costs more than twice as much. Then again, if you only use half as many DIMMs it means you get expandability later, though now obviously at the cost of some performance. It’s always about the tradeoffs, isn’t it?