DDR DRAM FAQs And Troubleshooting Guide

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

Why Doesn’t DRAM Run At Advertised Speed?

This is probably one of the most frequently asked questions about DRAM these days, especially since, for all intents and purposes, 1600/9 is considered the basic entry-level speed for newer systems.

Motherboards are designed to accommodate nearly any CPU compatible with their processor interfaces. But the capabilities of each CPU's memory controller can vary greatly. To that end, motherboards are designed to start new DRAM to a preset default data rate that any and all CPU/MCs can handle—typically DDR3-1066, DDR3-1333 or DDR4-2133. A few modules default to DDR3-1600 or DDR4-2400, but manufacturers rarely use those options. If you have DRAM faster than the default, it will have to be set up to run at the specified data rate for your particular kit. See the XMP, AMP, DOCP and EOCP descriptions in item No. 5and the configuration in item No. 14.

An exception to this is the new Kingston HyperX Fury line, which employs plug and play and, when installed in a supported motherboard (chipset), should automatically set itself up to run at its maximum data rate, up to and including the advertised specification.

You generally have two options for setting up the DRAM: manually, which many enthusiasts prefer in order to get the highest data rate and tightest timings, or, if you're dealing with a 1600 MT/s or faster kit, through an XMP profile (the Fury line is one of the few exceptions).

With an Intel motherboard and some AMD motherboards, you simply enable XMP in the BIOS and generally select profile one. From there, you are ready to go (if your CPU can handle the given data rate). Not all CPUs can handle every data rate, so you may have to set it up manually.

If you’re using an AMD motherboard, it may support XMP. However, it's more likely that it will have an option for DOCP or EOCP, which takes data from the XMP profile and translates it to the appropriate preset timings of the BIOS. With these motherboards, check the timings when you’re done, as the manufacturers often set them looser (higher than the timings the XMP spec provides for). Tightening them to the XMP profile can provide better performance.

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