DDR DRAM FAQs And Troubleshooting Guide

Low CAS Latency Or High Data Rates?

Neither. DDR3-2400 CAS 12, for example, has 50 percent more bandwidth than DDR3-1600 CAS 8, but both of them take the same amount of time to initiate a transfer. Large packets of data will speed up nicely with the added bandwidth, but many of the programs we use show no appreciable difference, though you will see performance improvements when using the higher data rate DRAM in things like multi-tasking, working with video, imaging, CAD, VMs or applications that use large data sets.

Want to get ahead of the game? Look for a good combination of the two, like this:

1600/7   1866/8   2133/9   2400/10   2666/11   2800/12

Each of the above progressions will provide slightly better performance. Also, there are times when a lower data rate DRAM with tight timings will outperform one with a higher data rate. For example, DRAM that runs at 1866/8 will outperform 2133/10 or 11 DRAM.

You can find a tighter CL at those frequencies. Both Corsair and G.Skill have CL9 sets in 2400, and you can find a few sets of 2133 with a CL of 8.

I tend to stay away from any DRAM at 1333/10 or 11, 1600/10, 1866/11 and up and so on. With those timings and with pricing as it is, you can often find a lower data rate set of DRAM that will outperform higher data rate DRAM for the same price.

  • Nuckles_56
    Thank you for this useful and informative article
  • das_stig
    With AMD motherboards, you should set the memory to unganged mode for a tiny performance improvement unless you're running a webserver.
  • vicstead
    Thank you Jim for this very informative article, an enjoyable read.
  • Mahruay
    Nice read although could you explain what real world improvements can be seen in faster RAM.
  • boju
    Nice article, answers a lot for people and definitely will link for future references. I need to ask though, is there any reason to discriminate DDR3 as per title?
  • TechyInAZ
    Wow this is very informative thank you for this!!
  • MPA2000
    Lost me after Virtual v Physical.
  • clonazepam
    I hope the next part covers performance when using say 3 sticks, where 2 are dual channel, 1 is single channel. Some real world results would be stellar (maybe as a follow-up?)

    I'd also like to see RAM drives covered. Suppose you allocate 4GB out of 16 for a RAM drive. How does the software create the 4GB? Is it using a single chunk of memory, is it taking 1GB from each of the 4 sticks? Is it from the beginning, middle or end of the 16GB of memory?

    Covering how to identify true "memory leaks" versus a more common scenario where RAM usage grows intentionally from the caching of more and more assets.
  • damric
    Great article, Tradesman! I give it Two thumbs up and two big toes up too!

    Only 1 issue:

    Ganged vs Unganged: that actually doesn't have to do with single or dual channel.

    Quote AMD:
    Ganged mode means that there is a single 128bit wide dual-channel DRAM Controller (DCT)
    enabled. Unganged mode enables two 64bit wide DRAM Controllers (DCT0 and DCT1).
    The recommended setting in most cases is the Unganged memory mode. Ganged mode may allow slightly
    higher Memory performance tuning and performs well in single-threaded benchmarks.
    Depending on the motherboard and BIOS, it may be required manually setting the timing parameters for each
    DCT (in Unganged mode) when performance tuning the memory or fine tuning the timings. Some BIOS
    versions apply the same timings automatically for both DCTs in an Unganged mode.

    Unganged is like a normal divided highway with two directions. Ganged let's traffic use all of the lanes in one direction at a time. Unganged is said to be more efficient but no one really ever tested this thoroughly to see if any applications would be better served in ganged instead. You could still have unganged single channel or dual channel, and ganged single channel or dual channel. If that's confusing I'll try to explain with more complicated interstate highway anecdote.

    Lastly, I see you have a new AMD rig. Did your head explode when you saw how much more difficult it is to tune memory on that platform than on your past intel rigs?

  • Shankovich
    Awesome article! These kinds of articles is what brought me to Tom's in the first place years ago!