Problem with 6GB of ram

Hello,
i have just installed windows 7 64-bit ultimate, and i have 6GB of ram, 3 X 2GB, DDR3, FBS 1600, but W7 shows 4GB of ram, what is the reason ???
Thank you in advance.

Are you sure its 64-bit? check system info in control panel to confirm. Also check your motherboard can take 6GB of memory.

mine has a max of 8gb - I have 6gb but Win only can use 5.5 gb as 500mb is used for hardware. I am also assuming 8GB is the max memory mapping for my MB so 2gb of "hidden memory" mapping is used for hardware as well.

Remember in some cases twice as much memory is used in 64-bit compared to 32-bit as 32 x2 = 64

To double the amount of addresses one additional bit is all the is needed.
32-Bits = 4_GBits of addressing
33-Bits = 8_GBits of addressing
34-Bits = 16_GBits of addressing
35-Bits = 32_GBits of addressing
36-Bits = 64_GBits of addressing
-----
40-Bits = 1,024_GBits of addressing
48-Bits = 262,144_GBits of addressing
64-Bits = 17,179,869,184_GBits of addressing

Each bit is a binary switch. Each time you add a binary switch you double the amount of addresses the operating system can address.

If you are using a 32-bit operating system. The maximum amount of addresses is 4_GB. Remember everything in the computer needs addressing. After all hardware has been addressed then the remainder of the addresses can be alloted to system memory. This is why a 32-Bit operating system cannot address all 4GB of memory.

If you are using a 64-bit operating system. The maximum amount of addresses is 17,179,869,184_GB. This is a big jump from 4_GB. And they are now talking about 128-Bit operating systems as well.

This Windows 8 talk - can't be 128-bit thats gotta be BS. Thats a totally different architecture. I mean for me Win7 in my opinion is the real acceptance of 64-bit for PCs. When did 32-bit start out for PCs - 1989?

What is your motherboard?