sometimes it's not as simple as running a memory test program to determine if it's "bad ram".
about RAM and motherboards
always check your motherboard manual for proper memory slot configuration.
according to this memory article and intel's article, and crucial memory's article (which is more accurate), a quad channel architecture like this has a 256-bit data bus, which is REALLY WIDE, and I wonder how the mobo mfr's can get that many traces in such a small space. is this for real? I had multiple troubles routing even 1 trace between IC leads doing my "acid bath" circuit boards. I am kind of wondwering if the bus is 128 bits and the guy who wrote the article made a mistake.well, as it turns out, this is not real.
according to this DDR3 memory pinout, the data bus (DQ0-DQ63) is 64 bits wide (verifying what others have said). Crucial, who makes RAM sticks, has said that 'n-channel'-memory architecture is essentially staggared memory. it seems odd to me that the data bus could be "128 bits wide" when the ASUS P79X79 quad-channel memory motherboard (see manual) (which takes 8 DIMMs) can have just 1 stick in place (and so can many lesser motherboards,at a perfoermance penalty). my guess is the data bus on the motherboard is 64 bits, and 1 and 2 just are halves of memory but constitute separate memory buses, and A, B, C, D for a given 1 or 2 should have the same type of memory in it (at least that last part is what this mobo manual says).
my little surprise
I have a dell poweredge 600sc server, it has a problem with the chipset or somewhere on the motherboard, because the memory address where the problem is MOVES AROUND depending on how much memory I put in! even with new RAM!
if you have more RAM than will fill 1 set of channels, try swapping the RAM around and see if the bad memory address changes. if it does, then it's the RAM. if it doesn't, then it's the mobo. you have to do this right, because mobos have multiple channels. get an antistatic wrist strap from radio shack (the expensive one).
at first I thought it was faulty RAM so I bought replacement RAM. memory test programs show a RAM failure at 2 addresses (one of them flaky) now I know it's not a RAM failure...
what I haven't figured out yet
I am not entiirely sure I understand "channels" yet in newer PC architecture yet. it seems like motherboard manufacturers who have quad channel architecture mix channels together when adding some amounts of memory, but they use up 1 first (this is not a channel), at least for the ASUS P79X79 motherboard. see my comment about 256 bits (routing 256 wires/traces).