Yeah the corresonding slots between A and B always match.  If I put just the DIMMs of a particular size in (so either all the 8GBs only, or all the 2 GBs only), things work fine.  It's only when I mix them within a bank (while still matching between A and B), that the machine won't even POST.  I'll put it to bed for now, I'm glad to hear I understand the docs right, I'll just have to be super careful when buying my next upgrade.  Thanks for you thelp.
Hi, I am struggling to understand all the options I have when adding memory to our R510 server.  It is dual processor.  I understand the layout of 3 channels per processor with slots A-1 and A-4 making up a single channel.  Where I'm having trouble with is if memory of different sizes can be mixed.  The statement in the manual that is throwing me off is this: "Memory modules of different sizes can be mixed in A1-A4 or B1-B4 (for example, 2-GB and 4-GB), but all populated channels must have identical configurations." When I had first read this I understood 'A1-A4' as meaning all of the slots, A1, A2, A3, A4.  I think it means only A-1 and A-4 though since they are two slots making up a single channel.  If it is just referring to A-1 and A-4, it still doesn't quite make sense to me because how would you ever mix sizes in these two slots and have them equal the size in slots 2 or 3?  Meaning, if I had a 2 GB and 4 GB DIMM in 1 and 4, that channel is 6 total.  If I understand "all populated channels must have identical configurations" to mean the same amount of RAM in GBs, it would mean slots 2 and 3 would need 6 GBs each.  Unless "all populated channels must have identical configurations" means the channels that correspond to each other on both procs? If someone can explain to me what I'm missing and give an example of how you could mix RAM sizes (assuming all the same speed and all dual ranked), that would be great.  Thanks!
R510 - memory upgrade options