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.

Why Does CPU-Z Indicate Single-Channel Mode With Two DIMMs?

If you see the DRAM showing as "single channel" in the Memory tab of CPU-Z and you are running two or more memory modules on a dual-channel motherboard, there are a few things that could be wrong:

  1. The memory modules may not be in the proper slots. Your manual should show the correct slots for the DRAM. Generally, a four-slot motherboard should use (from the CPU) slots one and three or slots two and four for a two-DIMM setup, or slots one through four for a four-DIMM setup. Most dual-channel motherboards color-code the slots for you to fill for dual-channel operation. If you’re using an odd number of memory modules on a dual-channel motherboard, you can use flex mode, which allows different sizes of DIMMs to work together. Flex mode is covered in item No. 7.
  2. If it’s an AMD motherboard, there is often a setting in the BIOS for ganged or unganged mode. You can manually set the DRAM to unganged (basically, single-channel mode) or ganged (dual-channel mode) regardless of which slots the modules are in.
  3. It’s possible the system isn’t seeing your entire amount of DRAM. Ensure that it’s showing the full amount of DRAM installed. For example, it may show only one DIMM even if two are installed, or it may be showing both but only half the amount of DRAM that it should. This can have a number of causes:You may have a bad DIMM. Pull and clean the gold contacts. I suggest using foam swabs and isopropyl alcohol (rubbing alcohol). Erasers can leave a gummy residue. Q-Tips or cotton swabs can leave fibers on the contacts. Check each DIMM individually to ensure it can boot the system by itself. If both boot up the rig, then move to he next suggestion. If you have another set of DRAM available, try those.It could be a single bad slot. Pull the modules and blow out the slots with compressed air. If they were in slots one/three, then try them in two/four. Some motherboards show a preference for one set of slots or the other. If you determine it’s a single bad slot, then it’s time to RMA the motherboard.It could be a bad channel on the motherboard or the memory controller (MC) located in the CPU. If the memory modules are in slots one/three, try them in one/two and see what you have, and then try them in three/four. If both show up and the full amount of DRAM appears in one combination but not the other, then the one that doesn’t show may be bad, or the MC might be bad. If that’s the case, first try loosening the CPU cooler, then snugging it back down, but not overly tight.Your CPU cooler may not be installed correctly. Oftentimes, the CPU cooler gets tightened too much in a corner or side, which can throw the CPU out of level so all the pins don’t make full contact, and that can result in an error.You may have bent or broken pins; there may be debris or thermal compound in the socket or on the bottom of the CPU. Pull the CPU and check for these and other problems. If nothing changes, you'll have to take it to a shop or RMA the motherboard and/or the CPU.Look in MSCONFIG and see if Windows is limiting your DRAM. Go to START, and type MSCONFIG in the search box. ENTER > BOOT > ADVANCED >. Ensure the Max Memory box is unchecked.
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