Only half of the memory is usable...

Hello,



I own ASUS Sabertooth 990 FX mobo, CPU is 6-core AMD Phenom II X6 1095T. I bought 2 kits (= 2 times 2x4GB = 16GB) of Corsair Vengeance CMZ8GX3M2A1866C9. When I insert them into the slots, BIOS detects that the slots have been fed with the memory (they are visible under ASUS SPD Information) but it says that RAM has size of 8GB...

Windows 7 Enteprise 64 bit says that I have 16GB RAM, but usable is about 7.96GB.

Same with Kubuntu 14.04 64bit - dmidecode shows correctly that all 4 slots are fed with memory (4GB in each of them) but total memory is 8GB only.



I've tried to:

- reset CMOS

- reseat the CPU

- swap the memory modules between the slots to check if there's a faulty module or not

- cleaned the memory slots with air

- set the AI Overclock Tuner to D.O.C.P. and chose the profile which runs the memory exactly with the timings written in the Motherboard Qualified Vendor List...so it runs on 1866MHz now instead on the default 1333MHz; it's stable also, but I still can see just 8GB instead of 16GB



And what to check next ? I have no further idea. Any help would be appreciated.



Thanks !

Vladimir