I've been trying to diagnose this problem for a couple of days now. I've narrowed some things down.
Issue Summary
Previously, I had a 2x4GB DDR3-1600 MHz kit (CMZ8GX3M2A1600C9) running in dual channel mode on my motherboard. The motherboard has 4 slots and supports up to 32 GB and 2133 MHz.
I purchased a 2x8GB DDR3-1600 MHz kit (CMZ16GX3M2A1600C10) and immediately started having issues. Random BSoDs showing error c000021a, sometimes I can boot into Windows but the resolution is wrong, graphics card is not detected properly, other components fail to appear, applications fail to launch, etc. Running either of the DIMMs alone works in every slot.
Working Configurations
- 1x8GB in any slot
- 1x8GB + 1x4GB in slots A2/B2
- 2x8GB in slots A2/B2 + 1x4GB in slot B1
Strangely, the presence of another DIMM in a separate channel causes the 2×8 kit to behave correctly. The 4GB DIMM in question is from the previous 2×4 kit.
Ideal configuration is to run the 2×8 kit in A2/B2 for a total of 16GB.
What I've Tried
- Tweaking BIOS settings to ensure correct MHz were being applied
- Tried each DIMM in every slot
- Lowered speed to 1333 MHz
- Tried enabling X.M.P. Profile #1
- Used "OC Tuner" to automatically set clock speeds
- Applied default settings in BIOS
- Performed a full power cycle, unplugged cord, switched off PSU
- Performed full BIOS reset with jumper
- Updated to latest BIOS
- Two full passes of both Memtest86 and Memtest86+ showed 0 errors
- Confirmed both sticks are truly identical via CPU-Z
- Tweaked CAS timings
- Slightly increased voltage (1.5 to 1.52)
The Kicker
When I install one of the older 4GB DIMMs alongside the new 2x8GB kit, everything runs fine. No more BSoDs, no driver or performance issues, etc.
Notice that CPU-Z sees the 4GB DIMM with a lower bandwidth of 667 MHz even though it tests at 1600 MHz. It also has an older XMP version and the CAS timings are different. I've tried to adjust the CAS timings for the new kit to match the older one and this yielded no results.
This has led me to believe it has to do with the motherboard settings, as when the 4GB is installed, something must be changing that allows the 2x8GB kit to behave.
What am I missing here? Why does the 2x8GB kit misbehave but running either 8GB DIMM alone or running both alongside a 4GB DIMM works fine?
Best Answer
Never found a true solution, but I had been planning to upgrade to Windows 10 for some time. I did that tonight and then tried putting the 2x8GB kit back into the machine on its own. The issue is now gone.
It seems Windows 7 was somehow the culprit, but it doesn't explain why the 2x8GB kit worked fine alongside an additional stick of 4GB. It must have been related to software in some way.