When I put in more RAM, the OS uses less than before

Trying to help a friend out with this, but I've never had this problem before so I'm asking for help here.

So he had 2x2GB sticks (different for each). Then he bought 2x4GB sticks that both were the same brand (Corsair). All of these sticks are 1333 DDR3.

The problem was that when I put in all 4 sticks, Win7 said that there is 12GB of RAM, but only 6 GB usable. I later started running memtest86 and even there it said there is 6GB of Memory (about 6134 I think).

So I took them all out and only put in the 2 new ones (2x4GB), note that the motherboard has 4 slots - #1 and #2 are one color and #3 and #4 are a different color. From what I understand, #1 and #2 run in dual channel mode (and #3 and #4). So I put the 2 new ones in and Win7 said that it has 8GB and used all of them too.
Then in the 3rd slot I put in one 2GB stick and Win7 said that it now uses 10GB (all of it too).
And then when I put in the 4th stick in, the OS said that it has 12GB, but only uses 6GB.

So in the end, I put in more RAM, but that resulted in the PC having less than before :heink:

At the moment I'm running memtest with all 4 sticks in, waiting for results.

What do you think is the problem?
5 answers Last reply
More about when before
  1. Is your Windows x64 our x86 ? ? Also check bios for updates, and check with different ram if you can.
  2. ^ His windows shows more than 4 gigs for use so must have x64 bit.
    1) it is highly recommended that when using multiple memory modules that they are the Same speed, same CL rating and same Voltage.
    Most likely Bios is incountering a problem enabling all four slots in daul channel mode due to mismatch of fourth stick.
    2) Some mother boards have a problem when all four slots are populated do to loading - Most likely not your problem but is a remote posibility.

    MAKE sure that you are using the latest Bios FW version!

    PS there is VERY little performance benifit going from 8 Gigs to 12 Gigs. Bottom line is just use the two MATCH 4 gig sticks for 8 Gigs of ram, Or if MUST have >8 gigs Ram then buy a 2nd set that matchs the speed, CL and Voltage ratings to the 2 x 4 modules.
  3. I agree with RetiredChief. Your friend is best off just running the two 4 GB sticks for a total of 8 GB. Get the performance benefit of dual channel. Unless he's trying to run some CAD program or Photo Shop there isn't a lot of benefit in gaming to have more then 8 GB right now. Sure it can help, but 8 GB is the sweet spot.
  4. Does dual channel really change the speed that much? I was thinking of leaving the 2x4GB sticks and one 2GB stick in the third slot.
  5. Not sure, But is is posible that the two matched sticks will run in daul chanel mode while the third stich will be single channel. You can verify this by runing CPU-z and looking at the memory tab. Use the pull down box to select each stick and look at channel operation (rigth side).

    Two answer your question. Theoritically it should double the memory performance as twice as many operations can be completed per given cycle - practically never get double, how much, - not sure.
    Explanation: http://en.wikipedia.org/wiki/Multi-channel_memory_architecture

    As I, and others have pointed out the diff between using 8 gigs of Ram vs 12 gigs is MOCH-Nixs.
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