I have a Dell Poweredge C2100 I recently purchased, with two L5640@2.27GHz CPUs installed. I'm trying to max the memory and for some reason the middle banks are not seen? I tried every possible and impossible combination, the middle bank DIMMs are ignored. I’m losing 6 potential slots with precious memory. If I move the sticks from C0-C1-C2 bank into B0-B1-B2 bank (middle), they are not seen anymore. I even changed the motherboard, thinking it is defective. It has to be an explanation why the middle banks are not registering the memory.

Memory is not seen into B0-B1-B2 and E0-E1-E2 banks:

I can change the size of sticks from 8 to 16GB into any memory bank except middle ones, they are seen properly. As soon as I move or add any memory into middle banks, they are not seen by the system. I also played with the bios settings, no dice. Currently set to Independent.

I’m using Samsung memory, tested with Memtest86. The sticks are good, if I shuffle them into working banks, they are seen without errors.

18 x Samsung 8GB 2Rx4 PC3L 10600R 09-10-E1-D2 M393B1K70CH0-YH9 

I read the C2100 manual twenty times, thinking there is a pin or something that disables the RAM, could it be because I use L5640 2.27 processors? I mean I’ve seen in the past speed being throttled from 1333 to 1060 based on processor type but never having the bank completely ignored.