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?

Signed, 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.

Sincerely, Lifehacker

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


Comments

    The layout/density of the chips on each module can effect whether a mobo will post or not eg single or double sided, high or low density.

    thanks for explanation but i dnt really get the fact am looking for.

    Thanks for the explanation! I would have had to go through multi-page tutorials filled with superfluous information just to find this kind of stuff usually. This is succinct and to the point.

    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?

    This is probably too late for you, Sam, but CAS Latency is the "timing" being referred to here.

    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.

      I would just like to point out that in think it's funny your running around with that size RAM. I, on the other hand, am happy with my 32 GB :)

    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.

    That post was back in 2012. Also, he did say old PC. Stop trying to brag about your 32gb, more ram doesn't mean you have a bigger dick, dick.

    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!!

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