DDR DRAM FAQs And Troubleshooting Guide

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.

Will Quad-Channel DRAM Work In Dual-Channel Motherboards?

When you see a four-DIMM set of DRAM advertised as quad-channel, that's marketing at work. You can easily take that same set and run one DIMM in single-channel mode, two DIMMs in dual-channel mode, three in tri-channel mode or all four in either quad- or dual-channel mode.

Each stick of DRAM is an individual 64-bit device and runs as such. On a dual-channel motherboard, with two or four modules in the proper slots, the MC (memory controller) sees all the DRAM as a single 128-bit device. If three are in an LGA 1366-based motherboard or configured as tri-channel in an LGA 2011 motherboard, then the MC sees all the DRAM as a 192-bit device. Four DIMMs set up in the proper slots of an LGA 2011 motherboard for quad-channel mode are seen as a 256-bit device, rather than four 64-bit devices.

I’ve seen many people buy a four-module set with the express purpose of using two modules in two separate motherboards. However, this is rare because, usually, the four-module sets cost a little more than if you were to buy two equivalent two-module sets. This is because it takes more testing for the manufacturers to match up modules for a four-module set.

Jim Reece
Topics
DDR3
Memory
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