Mixing and matching RAM?

Discussion in 'PC Hardware' started by Juniper Phoenix, May 27, 2016.

  1. Juniper Phoenix

    Juniper Phoenix MDL Novice

    May 2, 2016
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    So I have a HP Compaq DC7900 CMT desktop, that came with what appears to be the two 2GB sticks of DDR2 667MHz DIMM RAM. (It has four RAM slots.) I went to the local computer parts place and got another two sticks of 2GB RAM, which ended up being 800MHz RAM with slightly faster timings. From what I'd seen on the computer manual the MC and mobo can handle this fine, and it did for a long time before I noticed when I started to use the 6-8th GB of ram, stuff would start to freak out. I ran Memtest86+ and after a while I figured out that that stick had one bit that was defective, so I tossed the stick and put the other in a bag. The computer has only the stock sticks of RAM now and I was curious if there's any real serious issue with mixing and matching RAM sticks from wherever. I have seen both sides, that it will destroy your mobo and hardware, and that it will do nothing, but all my computing life I've mixed and matched weird RAM (my media server laptop has 3gb in two SODIMMs, one from an apple laptop) and never had problems.

    tl;dr (as well as question) would it be a bad idea to get another 2GB stick and go back to 8GB RAM?

    Thanks for reading! First new topic for me. :biggrin:
     
  2. MrMagic

    MrMagic MDL Guru

    Feb 13, 2012
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  3. Juniper Phoenix

    Juniper Phoenix MDL Novice

    May 2, 2016
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    Can/Does the mobo and MC do that automatically? I've never messed with the timings and voltages, nor do I know how, I just usually stuck the RAM in and it chugged along.
     
  4. MrMagic

    MrMagic MDL Guru

    Feb 13, 2012
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  5. bpwnes

    bpwnes MDL Member

    Aug 11, 2015
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    If all the sticks are good then it might be that the BIOS doesn't like the different timings. In most systems timing differences are okay, but I have run across some that don't like it. You can check for a BIOS update and that might help. I've seen "improved memory compatibility" listed in some BIOS update release notes before.

    I have some old servers here that do not like different timings at all, even if the memory is compatible with it. That being said, I also have an ASUS 1366 board with 11GB of RAM in it, all of which is just random DDR3 I had laying around, and it has run fine for years w/o a single issue. Some motherboards are just picky.
     
  6. Juniper Phoenix

    Juniper Phoenix MDL Novice

    May 2, 2016
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    Well, the fourth stick of ram was totally bad, but I put the working 2GB stick into slot 3 and the BIOS reported Flex mode, and everything is working a-okay with 6GB of RAM. The BIOS is fully updated and whatnot as well. The sticks that came with the computer have up to JEDEC #3 and go at 6,6,6,18,24 at 1.8V, and the odd one out goes 5,5,5,18,23 at 1.8V. The memory tab shows it going at 5,5,5,15. tRC didn't show up in the Memory tab. Thanks for all the help, it looks to be working fine!