DDR DRAM FAQs And Troubleshooting Guide

References
By Jim Reece
published

DRAM is probably one of least understood components in a computer. Here are answers to our readers’ most common questions about memory.

How Do I Set DRAM To Run To Spec?

To answer this question, we’ll have to break it into AMD and Intel. We’ll take a look at Intel first. 

Setting up DRAM on Intel rigs is fairly straightforward and easy (most of the time). Usually, there is DRAM that runs at less than 1600 MT/s and DRAM that runs at rates higher than 1600. Check your manual for the preferred slot selections (usually slot one/three or two/four on dual-channel motherboards), and look to see whether the slots are color-coded. With DRAM 1600 and up (with a few exceptions), you get XMP profiles in the SPD of the DRAM. With XMP DRAM, you simply enter the BIOS, enable XMP and select Profile 1. Depending on the actual XMP settings, you can try Profile 2 for a slight performance boost.

If there are any problems, try the following steps:

  1. Make sure you have the latest BIOS.
  2. Ensure your CPU is capable of running the frequency/data rate. If both of these requirements are met but the memory isn’t stable, a small increase in DRAM voltage or MC voltage might be needed. On Intel, I usually suggest about +5mV (0.005V) to either the DRAM voltage, the MC voltage or both. To locate the MC voltage, look for something like CPUVTT, DDRVTT, QPI/VTT or VCCIO. Some motherboards incorporate the MC voltage into the system agent voltage or VCCSA; this is seen most often in LGA 2011. Exercise caution by checking to see what other users have found to be safe and beneficial.
  3. If automatic configuration methods like XMP aren’t available, you can attempt to manually set the timings and voltages to rated levels.
  4. You can also check with the DRAM manufacturer (your best bet) or ask in the forums. We have many knowledgeable members and some DRAM tech reps, and I’m there daily.

AMD setup involves a few minor differences. Whereas with Intel, you look for XMP in the BIOS, an AMD platform without an explicit XMP setting might still have DOCP, EOCP or AMP. These are all ways to enable auto DRAM setup.

DOCP, EOCP and XMP on AMD appear to read the Intel XMP data from the SPD and then apply what the BIOS programmer considers best for a given AMD frequency, which often can be a bit looser than the specifications of the DRAM.

The same steps can be implemented for troubleshooting. Make sure you have the latest BIOS, and with AMD in particular, make sure your CPU can run the frequency/data rate. With AMD, it's much more common to have to add voltage to the DRAM and/or the MC (usually the CPU/NB voltage on AMD motherboards).

Jim Reece
47 Comments Comment from the forums
  • Nuckles_56
    Thank you for this useful and informative article
    Reply
  • das_stig
    With AMD motherboards, you should set the memory to unganged mode for a tiny performance improvement unless you're running a webserver.
    Reply
  • vicstead
    Thank you Jim for this very informative article, an enjoyable read.
    Reply
  • Mahruay
    Nice read although could you explain what real world improvements can be seen in faster RAM.
    Reply
  • 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?
    Reply
  • TechyInAZ
    Wow this is very informative thank you for this!!
    Reply
  • MPA2000
    Lost me after Virtual v Physical.
    Reply
  • 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.
    Reply
  • 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?


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