RAM not compatible

NoahL asked:

I’m new here and new to servers in general, so I might just be overlooking something. I recently was given a few free Apple Xserves (3,1). I decided I would try to build a single better server from all of them so took some 2GB RAM sticks from one of the Xserves and added it on to a board with 8GB RAM sticks. When I tried to boot up the server, it wouldn’t boot and the system activity lights were flashing, indicating a DIMM error. Could these RAM sticks be incompatible? They both came from an Xserve 3,1 and I know all of the RAM works. The server boots fine with just the 8GB sticks or the 2GB sticks, just not the two together. Both sticks are 1066 MHz DDR3 ECC. Thanks!

My answer:

The Xserve Setup Guide states that all the DIMMs must be identical. Therefore, you cannot mix different sizes of DIMMs in the same Xserve.

(Note that identical means that they must have the same specifications for size, speed, and timings. They don’t necessarily have to be the same brand, but using RAM that Apple didn’t sell you may invalidate the support contract you don’t have anyway.)

Also note that you need to install the DIMMs in specific slots depending on how many DIMMs you have and whether the server has one or two CPUs installed. The Xserve Setup Guide has an illustrated display showing which slots to use.

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