Dual Rank Memory - Is there a performance advantage?

Posted on 2007-07-24
Last Modified: 2013-11-10
Hi - I know there are already a few threads relating to the single vs dual rank memory arguement but can anyone tell me if there is any performance benefit in using dual rank memory in a server.

I am speccing a large server to run SQL Server 2005 and need to know whether to go for the dual rank memory.

The single is cheaper but cost is not relevant. I need to be able to deliver best performance.

Question by:stevemjp
    LVL 63

    Expert Comment

    It depends on the Server hardware, and whether it supports 2 DIMMS to increase speed.

    Check the Server specs. In general I have not seen this. so I would not bother.

    I hope this helps !
    LVL 70

    Expert Comment

    The maximum performance of your memory subsystem is achieved if you utilize all four ranks in each memory channel.   Whether you do this with four single-rank DIMMs, or two dual-rank DIMMs doesn't matter.   So the answer to your question depends on the memory configuration you're using.  

    If your system supports dual channel memory, then you want to have 4 ranks in each channel ... in this case that's often achieved by using four dual-rank DIMMs (two for each channel).

    Do NOT, however, mix single and dual rank DIMMS ... that will tend to reduce performance, as the chipset will not be able to uniformly distribute addresses.

    LVL 55

    Expert Comment

    I don't see why you shouldn't mix ranks; say you have 6 slots of interleaved RAM available on the motherboard, one dual rank 4GB pair plus two single ranked 2GB pairs does uniformly distribute the memory surely?
    LVL 2

    Expert Comment

    i think garycase ment dont mix duel and single rank in paired slots.

    most MB that have say 4 memory slots will have 1 and 3 and 2 and 4 as seperate channels.

    so if you put memory in slots 1 and 2 they will run as single channel mode. however if you put the same modules in slots 1 and 3 they will run duel channel.

    however you should not mix single and duel channel modules in the same MB channel :)

    so you could have single rank pairs in slots 1 and 3 and duel rank modules in slots 2 and 4 and be ok.

    but not single modules in slots 1 and 2 and dule modules in slots 3 and 4. as this would result in mismatched pairs and reduce proformance.
    LVL 55

    Accepted Solution

    It's pretty much irrelevant now since bank interleaving depends on the motherboard and they have changed quite a bit in the last 6 months. Delete is fine by me.
    LVL 70

    Assisted Solution

    The interface technology hasn't changed --- it's still faster to use fully populated channels (four ranks in each channel).   My original answer is still correct ... but I really don't care if the question is simply deleted or not => although, as always, it would be best if stevemjp would return and either select the answer he found most useful, or ask that the question be closed if he didn't find the information useful.


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