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AMD build with 8GB memory, 64-bit Win 7, but bios only reports 4GB, and Windows reports 3.90 GB usable, single channel.

post #1 of 5
Thread Starter 
UPDATE: For future Googlers (because I know how frustrating it can be to find a thread about your exact problem, only to see that it fizzled out with no closure).... it turned out to be a defective motherboard -- a boring solution, I know, and probably one I should've presumed from the beginning, but I know how finicky AMD mem controllers can be about RAM sometimes, so my knee-jerk reaction was to consider issues with memory compatibility and the mem controller itself. But as it turns out, the first M5A99FX PRO R2.0 simply had two bad DIMM slots (both on Channel B). It's the first time I've ever seen a board with malfunctioning DIMM slots where the RAM was actually recognized as installed but not usable. In my experience, bad DIMM slot = doesn't see RAM.

To be sure it wasn't an issue with the case shorting something or the cooler backplate warping the board, I ran the old motherboard outside of the case and used the stock AMD cooler. Result was the same. (There's always the possibility that I unknowingly did something in the very beginning that permanently damaged the board, but that would be a first for me. I inspected it closely and found nothing physically wrong, at least to my non-engineer eyes).

Anyways, returned the old board, and the new board worked perfectly out of the box with the originally purchased RAM, at its rated settings I might add (2133, 10-12-12-31, 1.6v).

I recently helped someone assemble a gaming PC, and ran into an issue with the memory not being recognized properly.

The parts he purchased (The ones relevant to this discussion):
AMD FX-8320
ASUS M5A99FX PRO R2.0
G.SKILL Sniper Series 8GB (2 x 4GB) DDR3 2133 Model F3-2133C10D-8GSR - Timing 10-12-12-31, voltage 1.6v
(I did not expect it to run at 2133 necessarily. It was merely on sale and cheaper than 1866/1600 kits at the time)

Symptoms/relevant facts:
  • Main BIOS screen shows 4096MB installed memory.
  • Under the Advanced tab in the bios, Northbridge Settings, the bios recognizes that DIMM 1 and DIMM 3 (and DIMM 0 and 2, when I tried that configuration) are each occupied with a 4GB module.
  • Windows control panel --> System shows "Installed Memory: 8GB (3.90 GB usable)"
  • CPU-Z shows 8GB installed as well, but Channel says "Single" (even though I do have them installed in a dual-channel configuration).


Things I tried:
  • Made super-extra sure that I had indeed installed the 64-bit OS -- yes, it is 64-bit Windows 7.
  • Cleared CMOS countless times tried different mem settings in the bios
  • Manually set speed, timings, and voltage to the mem's specs (won't boot at 2133, of course)
  • Tried frequencies all the way down to 1066 -- same result
  • Used the motherboard's memOK button -- same result
  • Reseated the RAM multiple times - same result
  • Tested each stick individually - recognized properly (all 4GB usable if only one DIMM is installed)
  • Tried other DIMM slots contrary to the motherboard manuals suggested arrangement -- same result
  • Ensured that "Maximum Memory" was unchecked in Msconfig boot advanced options
  • Ensured that Memory Hole Remapping was enabled in the bios
  • Inspected the contacts for any chips/scratches or contaminants of any sort. All clean.
  • Did the same for the DIMM slots. Clean.
  • Inspected the CPU for any bent/missing pins -- looked fine

Some of the more obvious things to try were not possible that day -- Didn't have a spare PC to test the RAM, didn't have time to run memtest, and did not have spare RAM or another AM3 CPU to test.

I was suspecting that the 2133 kit was a mistake, so the solution of the moment was to order a Corsair Vengeance 8GB 1600 kit, the exact model number that is on the motherboard's QVL (the sniper series RAM was not on the list, but since it was Gskill, I had assumed it would be fine.) That kit will come in the mail this week. He plans to install it himself (made sure he knew how), and if that solves the problem, he'll send the G.Skill back. Otherwise, I plan on driving back over there and continuing diagnostics.

In the mean time, I was hoping someone here has some insight, as it's been a while since I've had any hands-on experience with an AMD build (since Bulldozer). Probability that the Corsair kit will resolve the problems? And if it doesn't, what else should I be prepared to test next time I go over there? The next thing I am suspecting is a faulty memory controller on the CPU. frown.gif
Edited by StephenP85 - 3/10/14 at 10:59am
post #2 of 5
Is the RAM set to ganged or unganged mode?
Green Dragon
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Green Dragon
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post #3 of 5
Thread Starter 
I didn't touch that setting at all. The bios sets it to unganged by default. Ganged vs. unganged does not determine single vs dual channel, though. It merely changes the way the memory is accessed by CPU cores. There's no reason it should not run correctly as unganged (and 2x64 bit dual-channel is preferable over 1x128 dual-channel), but I'll add Ganged to the list of things to try for ****s n giggles, though.
post #4 of 5
Umm...updated BIOS? I'm not sure...
Green Dragon
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Green Dragon
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Windows 10 Professional 64-bit Acer G7 G237HLbi Acer G7 G237HLbi Acer G7 G237HLbi 
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post #5 of 5
Thread Starter 
Update:

The new RAM produced the same result. Tried a brand new 8320. Same result... mad.gif

Now we have a new motherboard on the way (same brand/model).

Thing is, the RAM is recognized and functions properly in the first two slots, but in single channel obviously. As soon as I put it in any dual channel configuration, only 3.90GB are usable. Tried ganged and unganged, no difference. It knows the RAM is there, just can't use it.

I've built probably somewhere just under 200 PCs, and I have never seen this happen. I have had motherboards with bad DIMM slots before, but it was pretty clear that the DIMM slots were bad. They straight up did not work.

At least wednesday, he'll be handing over the PC to me so I'll have much more time/resources to obsess over it and try every little thing. Suggestions on additional stuff to try is much appreciated. For some reason, I'm skeptical about it being the motherboard, but who knows. I've never used this particular board before.
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