One fix for this problem
Hello All,
I spotted this very issue last night on my new rig.... 8 gigs installed, ( 3.99 usable ) displayed in My Computer - Properties
Funny thing was that I know it wasn't there before, and I had just completed some decent overclocking in the last few days.
I was able to correct this quickly by remembering something I read about when trying to select the proper DDR3 memory / motherboard combination.
The note basically stated that if you intended on filing up all your DIMMs.. in my case... 4... you would not be able to run the memory in dual channel, and Windows 7 64bit might have problems... so they recommend buying 2 huge Dimms.. which were too expensive for me... etc...
Short answer... the memory I purchased was 4x 2 Gig Corsair DIMMs rated at 1600MHz..... and my motherboard stated it could run DIMMS at 1600GHz without overclocking them... but...
THAT IS ASSUMING YOUR CPU IS RUNNING AT STOCK SPEEDS....
Same with XMP profiles... they assume you have stock CPU.
If you go in and slow down your BLCK and/or memory speed to slightly lower than your max NON-overclocked DIMM speed ( 1600 MHz in my case ).... viola...
I am now running my i5 750 at a very cool temperature at 3.83 GHz.... and my memory at 1573MHz ( lower than the 1600 stated limit for my motherboard)... and
after slowing the ram down a touch and booting back into Windows 7 64bit... no more problem....
Motherboard was limiting access to the DIMMS due to the 4 DIMMS in dual channel.
Hope this helps someone... I was happy to not have to abandon my overclocking achievements all together.
Cheers,
Sin machine