What Are The Rules On Mixing Two Different Types Of RAM?

What Are The Rules On Mixing Two Different Types Of RAM?

Dear Lifehacker,

I’ve got some old RAM lying around that I’m looking to use. What are the rules on mixing RAM? As long as they’re the same modules (DDR, DDR2, etc), should I experience any performance issues?

Mystified Memory Mixer

Photo by Heather Greene.

Dear Mystified,

You are right about mixing different RAM modules — if there’s one thing you absolutely can’t mix, it’s DDR with DDR2, or DDR2 with DDR3 and so on (they won’t even fit in the same slots). RAM is pretty complicated, but there are a few things you can mix and a few things you shouldn’t. In any case, I don’t recommend it. If you’re buying new RAM, you’re probably going to make your life a lot easier by buying the exact same model as you currently have in your machine. That said, if you absolutely have to mix them, here are some general guidelines.

You want to make sure each stick has the same cas latency, timings and voltage. While you can tweak these settings in the BIOS to make the two sticks match (we briefly showed you how when we discussed overclocking your processor), I don’t know why you’d want to. You’d have to spend quite a bit of time messing around with it all and probably underclock at least one of your DIMMs in the process — and there’s no guarantee it would work even then. Really, it’s a lot more trouble than its worth.

Mixing RAM speed, however, is a slightly different matter. In theory, if you had to, you could mix, say, this Patriot model (DDR3 1333) with this Corsair model (DDR3 1600), since they have the same cas latency, timings and recommended voltage. Your motherboard would probably just automatically underclock the faster one and you wouldn’t run into any problems. Thus, it’s possible, but note that when you start mixing speeds, a chain is only as strong as its weakest link, so to speak. Your RAM will only run at the speed of the slowest DIMM, unless you wanted to overclock the others.

None of this necessarily guarantees functioning RAM, of course — you may be greeted with the Blue Screen of Death if your DIMMs just don’t like each other (or your motherboard doesn’t like one of the DIMMs). Most of the time, though, your computer will run fine if you mix different brands, sizes and speeds. If you’re just doing it to cobble together a second PC from old parts and don’t want to spend any money, that’s fine — but if you’re adding RAM to your current computer, I’d recommend getting the exact same type of RAM you already have installed. Memory is cheap enough nowadays that you’re probably better off just buying some new DIMMs and calling it a day — that’s the only way you’re going to get the best performance out of your PC.


P.S. If you’ve got your own tips and experiences mixing RAM, share them in the comments.


  • I understand CL and voltage but how do I match up timings? Am I looking for a data rate number such as 800 MT/s, or something like a 7.8US Refresh Interval (8192 CYCLES/64MS)or does timing just refer to the speed like PC2-6400?

  • I had a friend with an old PC and I also had an old PC and one of my 64 Sdram sticks was buggy, so I thought I could use one of his. When I first booted the system, it showed I had 128mbs, so I was happy, but once XP started to boot, it did a memory dump and squealed like a stuck pig! Haha. Couldn’t get it to ever really boot after that. I took out each stick and tried them separately and of course, the one from my friend’s PC made my PC squeal. So I just took it out and all was back to normal. So just to verify, my PC uses th 183 pin? type (forgot the number but you know what I mean) currently with one 64mb stick (the other died) and the system can acommodate up to 512 (i.e. two 256mb sticks). The stick I took from my friend’s PC was a SYN DIMM and although it did say “100” I guess something like voltage? or something was not compatible.

  • Hey guys, thought id share this. I had an old board from gigabyte that i wanted to upgrade the ram on, which ran fine with the 512mb it had in it until i removed it to see what it took and reinstalled it. The system would boot up give a blue screen of death and restart over and over. Im saying this just in case you have the same problem. What happened was when i pushed the ram back in most of the solder points n the bottom of the board broke loose and caused this problem. I fixed it by resoldering all 200 or so points.

  • Thanks for this. 🙂 One question: suppose I put in some ram that turns out to be incompatible and my system doesn’t boot or sh*ts itself in some other way; will this cause permanent damage to my computer, or can I just remove the unsuccessful sticks and be back to normal??

    • Way late to the game here but I just happened to notice your question and that no one ever replied. No, there is no reason it should cause any permanent damage to your computer, the only way you could cause permanent damage would be to try to force the wrong type of RAM into a slot, like trying to put DDR2 into a DDR3 slot, but that would take a lot of misguided effort. Beyond that, just remove the offending RAM module once shut down, and on reboot it should recalculate your RAM and run just fine.

  • Hi…
    I have a 2 slots of RAM in motherboard, In one slot i have 2 GB RAM, i also have 512 MB RAM, Now should i use that 512 MB RAM with that 2GB RAM? (Both are DDR 2 RAMs)…

    • Look at the memory type designation on the two RAM boards – Should be PC2-4200 or PC2-5300 etc. This indirectly indicates the speed. As stated in the article the motherboard will likely clock to the lowest common denominator (or not work or give unpredictable errors) if the speeds are different. So if your 512MB RAM is a lower number so slower you will be slowing your main 2GB RAM down for the sake of an extra 25% more RAM – not worth it!
      Best advice – throw the 512 away and buy another 2GB module (assuming it is 32 bit OS so 4GB maximum). Your PC and you will be much happier with the performance.
      There is a good free system scanner from Crucial (google crucial memory scan). That will recommend which of their products will be compatible with your PC and give prices new. Use that as a guide to suitable speed options (or just get the same speed as your existing 2GB RAM). No need to buy Crucial unless you want to but seems to be perfectly good memory. Could buy second hand on Ebay if you don’t mind the risk using the PC2-xxxx number from the scan or your existing RAM. I understand, but have not had the problem myself, that RAM from different manufacturers can have problems because of different latency etc. So to be super safe choose same make if possible.

    • Hay having 32 gb of ram his choice just means it take a lot longer to fill to compassity. Like he probly atracked to XXX size and meeds the lager ram just to down load the photo they sent him bahaha. Sorry i realy am i see a duck in a barrel 🙂

  • Hey there,

    I presently have 2x4GB 1600MHz RAM modules. I was thinking of upgrading one of the modules to Kingston 1600MHz RAM module, and may be sometime later upgrade the other module. Will this cause any issues on my laptop.
    Also suggest some good gaming RAM modules!!

    • Something I would like to note is that the voltage will cause issues. Ie a small but noticeable difference; 8 gb corsair xms 1600 1.65 V 8 gb corsair xms 1333 1.5 V. — This caused my computer to go into a permanent sleep mode where all I could do is restart the computer to allow it to function as normal. I think when you mix speeds it’s supposed to run at the slowest of the 4. Anyway fixed the problem. Now I am about to pair the 1600 corsair 1.5 V with crucial ballistx 1600 1.5 V.

  • hi

    If computer is having different ram memory means one is having 4 GB and another one is having 8 GB but same speed and voltage and also both are DDR4.
    1. Is the system will run peacefully? or else any problem will happen?
    2. Is the memory get shared with one another while opened more application?

    • Possibly, even probably, but your motherboard and/or CPU type might be more (or less) accomodating to different RAM sizes. Also, if your motherboard supports dual channel RAM, you might have to try different slots for each module to find the best configuration.
      According to my old ASUS P8-Z77 V-Pro motherboard manual, it can deal with different RAM module sizes, as long as the modules are all the same timings and voltages; it will also run part of the memory of a bigger module in dual channel mode if it’s on the same channel as another smaller module. I.E. if you put in a 4GB module on the 1st slot of channel A and an 8GB module in the 2nd slot of channel A, 4GB of the 8GB module will run in dual channel mode and the other 4GB of the 8GB module will run in single channel mode. I haven’t tried this, but it is in the motherboard manual.
      Your motherboard may not be as flexible; it might be necessary to put the different size modules in different channel slots (if the motherboard has more than on channel). Best to start putting them in the same channel slots (Channel A – slot 0 / Channel A – slot 1) and see if that works. If not, put one stick in a channel A slot and one on a channel B slot (check your motherboard manual for recommendations on which slots to use for the best speed and compatibility).

  • I have a similar question as sureshan.
    I have a 4 gig dd3 and a 2 gig ddr3 my computer seems to be running fine and speeds are good for me a general user. I put them in msi 760gm-p34,and loaded windows 10. But my current question is that on MSI website the latest drivers are up to windows 7 x64
    Any suggestions about drivers?

  • Hi There,
    I have Question regarding mixing RAM module,
    Actually I Have Notebook with 8 gb soldered to Mainboard. I Check Current soldered 8gb run with CL17 and speed 2400 MHz(PC19200). So my plan is adding another Ram Module into empty slot with 4gb (PC19200) in size. speed and CL remaining the same.
    Could you give me advise that it would Make my Notebook crashed or will some thing bad happen to notebook performance?
    Thank you very much

  • Hi,

    Out of my experience, nothing will be a problem except the latency. I have mixed a hynix 2GB and a Corsair 4GB RAM on a HP probook notebook and it’s working fine from the past 2 years.

  • I’m looking to buy more ram, since I only have 6gb. The ram I currently have is from my old Acer pc. I can’t buy the same kind of ram because it came with the pc, and it’s not sold anywhere. I have two sticks, one 2gb one 4gb. Can I buy another 4gb stick from a different brand? I don’t want to buy two new sticks, it would be much easier to just buy one.

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