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Using multiple tools, I have verified that my computer can "see" that 8GB of RAM is installed, but only is using 4GB of ram. I've seen this behavior with:

  • Memtest86+ 4.20: Memory SDP Information shows 2x 4GB DIMMs installed in Slots 0 & 1. CAS timings match BIOS. Also, Ram Clockspeed is at 532 MHz instead to 1033MHz.
  • Windows 7 64-bit: System Properties reports 8GB installed, 4 GB usable
  • Linux (amd64 kernel) utility 'free' reports 4GB or ram

System Specs:

i7 Processor
8GB DDR3 Ram
EVGA X58 SLI3 Motherboard
Windows 7 64-bit Pro
8800GT Video Card

I've verified the proper Slot locations on the motherboard. They are correct according to the manual.

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Is memory remapping enabled in the BIOS? Also, Memtest will show you the clock speed, which is different from the transfer rate (that's the whole point of DDR, to transfer twice per clock cycle). –  Ben Voigt Apr 25 '12 at 3:39
    
is the board a "tripple channel" type of board? Populate the 3 green slots only , then test what happens. Also with the memory controller now on the cpu, tearing off the heat sync and checking all the pin connections of the cpu becomes a fun thing to check when having a memory issue. some web reports exist of offset pressures of the heatsyncs and tiny damages at the cpu socket effecting few pins not connecting. IF (somehow) tripple works proper, the configuration for 4 dimms changes again, the order being filling the first 4 slots closest to the cpu –  Psycogeek Apr 25 '12 at 4:03
1  
If you only put one of the DIMMs in, do you still get 4GB RAM? –  Harry Johnston Apr 26 '12 at 4:43
    
Turns out it was a bad ram module –  Aquadisco Jun 21 '12 at 22:26
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