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Mixing different speed memory modules

I am running a MSI K7T266 Pro2 Motherboard (MS-6380) with 512mb or Crucial Memory # CT6464Z265 with the following stats - DDR PC2100 - UNBUFFERED - NON-ECC - DDR266 - Voltage: 2.5V - Memory Timings:CL=2.5.
I am trying to add a second 512mb module.  I found a great deal at TigerDirect on the following Ultra brand memory - DDR PC3200 - 400mh  - (I apologize, but no other stats are available...)
I can install either memory module into my PC and it will work properly.  I can do this in any of the three Memory Slots on the Motherboard.  When I install both together, the PC only sees 512mb of memory.  I have tried upgrading the BIOS, changing the BIOS settings, swapping the slots several times and everything else that I can think of.  
Can I mix these two types of memory in a PC?  From what I have read, I should be able to do this, but it seems that I can not.  Any suggestions?


1 Solution
you can check the compatibility at


but i think your mobo is just picky about them
I agree - in most cases, you can mix different speed RAM, but some motherboards just don't like it.

Generally, you can mix speeds, but you must operate the system at the speed of the slower of the two modules.  The problem can arise because most modern memory modules have an "SPD" chip (serial presence detect), a ROM that lets the computer "READ" the specs of that memory module.  If two such modules conflict, the computer might not configure the system in a useable manner (this would be a function of the BIOS code).  You can try a manual over-ride in the BIOS and see if that helps.

There are other incompatabilities that can arise, the general rule that you can mix speeds isn't hard and fast, it's just a guideline.

From your post, I'd say that you clearly cannot mix THESE two memory modules in that motherboard.

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