Can the M6400 support 5GB of ram ?

In 1Gb+2x2GB config ?

 

Yep, shouldn't be a problem.
Supports up to 4x4GB, any configuration below that should work.

 

Er, no there is some issue with pairing.
"From thw manual:

I'm confused as there is currently a single sodimm and its booting. So, can I put 2x2GB in slots B & C for a total of 5GB ?

 

Unless there is some magic restriction on the M6400, that's just on paper. If you put 2x2 in slots B and C I would be shocked that it does not boot. And if it doesn't... take out the single GB stick, simple solution.

 

When you use more than 2 slot, you need to have matched A&D and B&C modules --> 5GB is not possible, but you could get 6GB (2x2 + 1x1) or 8GB (2x2 + 2x2).

 

Guys, sorry but this is not true. You do have to match top with bottom modules but ONLY if you populate both. You can leave one of the memory modules open and populate it later.

 

So you're saying 5GB would work, correct?

 

Correct, it will work if configured correctly but the cost of adding another 1GB DIMM should not be that great.

 

Did you try this? My M6400 came with 4 GB and I had 1GB module left, so I put it in and it didn't worked, no matter which configuration I tryed, so I upgraded to 4x2GB and everything works fine. Well perhaps the 1GB module was defect.

 

I just tried this, and it WORKS.
My M6400 came with 1 GB, and I added 2x2GB for a total of 5 GB.

The user guide that came with the computer was incorrect.
The service manual is more precise, it says IF C is populated THEN B must be matched and similarly for A&D.
https://support.dell.com/support/edocs/systems/wsm6400/en/sm/memory.htm#wp1180190

Running memtest86 now.