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Mix and match RAM?

Discussion in 'Off Topic' started by Jeremy Paterson, Apr 1, 2011.

  1. I'm normally good about finding my own answers on the internet, but I'm a bit stumped with this one and afraid to take a chance.

    I was previously using 1 stick of RAM. Here are the specs:
    1 GB DDR2 667MHz (4-4-4-12) 1.8v
    Product Page

    I just bought a 2-pack of 1GB sticks with, as far as I can tell, the same specs.
    Product page

    I removed the old one and installed the 2 new ones per the Mobo manual (putting them in same-colored slots for "dual channel.") Computer started up and is running fine.

    Here's my question... would it be okay to install the old stick along with the 2 new ones for a total of 3GB? If there's a risk, I don't want to do it... I'll just buy another identical twin pack and go for 4 GB (well... 3.5 GB useable because I'm still using XP ... FTW!) I just hate to see that 1GB stick sitting there on my desk not doing anything.

    Any help here would be appreciated.
  2. You can add the third stick, you may lose Dual Channel mode but I doudt you would notice any real world difference.
  3. It should run without problems, set (in the BIOS) the ram timings to the lower ones of the new kit.
  4. Jim Cole

    Jim Cole
    Premium Member

    The computer will run fine, and as mentioned by Eyghon you will lose the dual channel mode, but you won't really be able to tell the difference unless you were running benchmark software or running some seriously ram hungry game.
  5. Thanks for the replies. Tobias, where did you see the timings listed for the new RAM. All I can find is CL=5. I can't find the other timings. If I set it to "Auto" in the BIOS, will it just match them up for me?

    Also, since I'll be losing dual-channel, which is better: 2GB dual channel, or 3GB single channel?
  6. Jim Cole

    Jim Cole
    Premium Member

    Performance wise, it would be better to have dual channel due to the system being able to access the ram on a wider bus, but if you are doing things that chew up ram like photoshop, it might be better to have the 3 gigs of ram in the system, that way you cut down on the disk cache access a bit.
  7. Here are the timings. The latter numbers might be different because of different modules in every production cycle, the right numbers are stored in the so called SPD on the modules itself and can be accessed through CPU-Z under Windows.

    CAS Latency (CL) 5
    RAS-to-CAS-Delay (tRCD) 5
    RAS-Precharge-Time (tRP) 5
    Row-Active-Time (tRAS) 15

    If you have a newer CPU than Pentium 4 or AthlonXP, dual channel is not a dealbreaker anymore. Modern memory controller either they are in the chipset like in the Intel Core (2) duo/quad series or in case of any other actual CPU on the CPU-dice itself, can work perfectly in normal desktop applications (games, big office suites, browsing) with a uneven count of memory modules.
    In some special applications (huge data mining software, file compression where only the raw bandwidth counts) it is better to use an even proportion of memory lanes and modules, but the loss are most small numbers which don't be noticeable without a benchmark. If you use a modern operation system like Vista or Windows 7, the larger memory pays of every time.
    CPUs are generally memory latency bound, thats why the CPU-caches and memory read ahead strategies are so important for the overall performance.
  8. I have an Intel Core 2 Duo. I tried it with all 3. I didn't run it long enough with only 2 to get a feel for it, so I can't really tell if it's better or not. I can DEFINITELY tell that it's better than only 1 though!

    When I boot up and it runs the POST, it tells me that memory is running in "flex mode" (it said "dual channel mode" prior to installing the 3rd stick.) I didn't make any changes in the BIOS.

    Anyway, things are running faster than they were before so I'll just leave it like it is.