64 bit windows using half of installed memory

[berry]

Hi, I'm well aware that this is a commonly asked question, however every thread I've read through I've tested all their fixed and am still coming up dry.

I'm running a 64-bit Windows 7 version on:
Motherboard: Gigabyte GA-P55-USB3
bios vers: Award Software F9
Dual Channel Memory: 4GB 2x2 in Channel 1, 8GB 4X4 in channel 2 (Corsair 1600Mhz, DDR 3 [every stick])
And its all colour matched so it's not like I can really mess that up
Cpu:Intel i5, Quad core @2.8Ghz (Generation 1 i5, no OC)

Windows is telling me that I have 12GB of Ram, but only 5.99 Useable.
I've gone into msconfig and ensured that I have no "maximum memory" set

Logically from what I can tell, Windows is letting me use Slot 1 from each channel, and just disregarding slot 2.

I've gone quickly through my BIOS but can't see anything that would be stopping me from using the other 6 gigs.

In my resource monitor it claims 6153Mb is "hardware reserved" and if I knew a way to find out what exactly its reserved by I would, but sadly I'm out of ideas.

Any other suggestions would be very much appreciated, thanks

 

[arunmohan]

http://www.tomshardware.com/forum/267749-30-windows-usable

 

[Raiddinn]

First go to start, run, MSCONFIG, BOOT.INI, advanced options, and see if the RAM box is checked and has a number in it. If so, either uncheck the box and restart or try changing the number and restarting.

If that is no go then do the following:

Try switching the ones from channel 1 into channel 2 and the ones from channel 2 into channel 1. See what happens.

If that doesn't work, you could consider the following:

Ideally, it is the best idea to just use 4 of the exact same stick type without mixing and matching different speeds and sizes etc. You might be able to avoid problems like these if you just throw out the old and buy another set of 2 x 4GB of the exact same part number as the 2x 4gb you have now.

 

[berry]

Best answer selected by berry.