Ram problem usable ram vs installed ram?

Everyone has answered your question correctly. The reason a 32 bit O/S. can only address -4GB memory is because in binary, 2 to the 32nd power:

2^32 = 4,294,967,296 bytes

In a 64 bit O/S 2 to the 64th power:

2^64 = 1.84467441 × 10 to the 19th power

Do you have a 32-bit operating system or a 64-bit operating system?

If you have a 64-bit operating system, the problem is that your BIOS is not remapping the RAM where the operating system can find it. Go into the BIOS settings and turn memory remapping *ON*.

If you have a 32-bit operating system, the problem is that the BIOS is remapping RAM where the operating system cannot find it. Go into the BIOS settings and turn memory remapping *OFF*. Note that this will only get you to about 3.5GB or so. 32-bit versions of Windows cannot address more than 4GB and about .3GB to .8GB is used up by other mappings.

Yep, you probably have a 32 bit operating system installed. You need a 64-bit operating system to be able to use that much Ram. Before you ask, you can't just download 64 bit and install it on a 32 bit. You won't believe how many people ask that lol.

You need to install a 64 bit operating system to use more.