Bad RAM Channel??

Hi Everyone,

Here are my Specs:
AMD FX-6100 (stock clock)
ASRock 990FX Extreme 3 Motherboard
Corsair Vengeance 8GB (2x 4GB) CMZ8GX3M2A1600C9B
2x hitachi 7200rpm 320GB HDDs in RAID 0
XFX Radeon 6870 GPU
750w PSU
Win7 Pro x64

All settings are BIOS default, except RAM clock is set at 1600 (keeps wanting to clock at 800 on auto)

I just upgraded the CPU, MB, and RAM on my Phenom I system to Bulldozer. I was able to POST, set up my RAID, install an OS, basically everything looked fine....until I checked my memory bandwidth.

Only 9GB/s, so clearly it's running in single-channel mode, even though I have the modules set up in dual mode (A1, B1 or A2, B2). Then I check Windows System Information, which lists 8GB installed, 4GB usable. Memtest 86 also only reads 4GB.

Then I performed these steps:
1) Update BIOS
2) Clear CMOS
3) Reseat CPU and RAM, clear CMOS again for good measure

Same deal. So then I remove one DIMM and test individual RAM slots. I get no POST with either DIMM in either of the Channel B slots. And no POST with both DIMMs in the Channel B slots. But Everything works fine with a DIMM in either of the Channel A slots.

Windows also reads 8GB installed and usable in Memtest and Win with both DIMMs in Channel A, although obviously it is running in Single-Channel mode. My bandwidth also went up to 10.9 GB/s after putting both DIMMs in Channel A.

The Corsair RAM is not on ASRock's list of supported memory for this board, but hell, The board supports RAM up to 2100(oc), the CPU 1866, and the memory is only 1600, 1.5v.
3 answers Last reply
More about channel
  1. Set your ram to 1600 in the UEFI BIOS.

  2. Thanks for the quick response. But I actually do have the RAM set at 1600 in the BIOS.

    But even if I did allow the BIOS to underclock it like it wants to, it should still POST in either channel, right?

    I don't think my problem is really the bandwidth, but why won't the system POST with RAM only in Channel B? I can't find anything that says a particular slot must be populated in order for the MB to POST.
  3. Got it fixed. I had a bad mobo. RMA'd it and everything is good now!
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