Doug at ClusterMonkey pointed us to a Nehalem memory cheat sheet put together for Dell’s technology wiki by Jeff Layton. The writeup looks like a pretty complete summary of the various options for configuring memory on a Nehalem, and what the impact of the various options is on memory performance.
Posted in HPC by John West
1 comment
Summary:
* 1 bank x 3 memory channels per socket is 1333 MHz memory (if CPU supports it)
* 2 banks x 3 memory channels per socket is 1066 MHz memory
* 3 banks x 3 memory channels per socket is 800 MHz memory
Thus, if you are going for large memory capacity, you can lose a large amount of memory bandwidth. For example, if you choose 8 GB RDIMMS and populate 2 banks x 3 memory channels, you can get 96 GB of memory with an 8.5% loss in bandwidth.
If you choose 4 GB RDIMMS and populate 3 banks x 3 memory channels, you can get 72 GB of memory with an 22% loss in bandwidth. Or you could go with 8GB RDIMMS for 144 GB of memory, but still with the 22% loss in memory bandwidth.
Since I like to purchase large memory systems at work, this turned out to be an eye opener for me. Thanks for digging this up.