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Corsair XMS2 CM2X1024-6400


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I have 2 matched pairs of this ram.

Unfortunately there seems to be a compatibility between the pairs.

The only difference i can see is 1 set is v5.1, while the other is v5.2.

While trying to run these all together, memtest fails or XP freezes on boot up.

Yet when i run the sets seperately they function fine.

Surely being the same brand & model they should all work together?


Thinking it was my motherboard i returned it and got a loan one. So i am now probably going to get a nice fee lol




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The memory controller can not keep up with the extra DRAM at the rated 6400 speed. You will need to drop the speed of the DRAM from 800Mhz to 667Mhz. If you had purchased 4 X 1024MB of PC8500 (1066Mhz) DRAM, then you would have had to drop to PC6400 (800MHz) DRAM, etc. 2 X 2048 will not issue this problem. This is a problem of all 4 B Banks being populated and is related to the on motherboard memory controller not begin able to load and access DRAM as fast with 4 Banks populated as it can with 2 Banks populated. You must slow the relationship down with 4 Banks populated.


Think of it this way. If you have a small phone book, then when you go into the index to find the page where you will find the phone number you are doing so at a certain speed due to the pages of the Index. Then you have to drive through the pages to get to the number. Now if your index is twice as large and the pages twice as many, then it takes longer to access the data. Now DRAM has a Strobe and the length of the strobe is how long the rows and columns can be left open before they must be refreshed. There is not enough time for the dram to be refreshed and then accessed with 4GB at the full access speed of the DRAM. The chipsets are optimized for 2GB, not 4GB and for 2 DRAM slots, not 4 DRAM slots populated. You can overclock the FSB (and hence the Memory Controller Hub = MCH) to gain some extra bandwidth and thus access the capabilities of the DRAM since the chipset is now clocked up. Usually when you clock up the FSB and concurrently the Memory Controller Hub (MCH) you need to raise the voltages of the CPU/MCH a bit as well.


Shut the system down and install two sticks. Enter the BIOS and set the DRAM to 667Mhz with 5-5-5-18 JEDEC timings. Shut the system down and install the second set of DRAM. You need to manually set this because the motherboard defaults to setting for 2 DRAM banks throughput, not four banks.

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Yes. They went through memtest fine.

I tryed 1 stick from the new pair to make a total of 3Gb.. System would post.. but memtest would show a huge drop in memory b/w and XP would load very slowly and be laggy once loaded.

Put in the last stick and system wont post.

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