Note that if you're using a 32bit version of Windows (like most home users) than your system will only use 4GB of RAM, even if your motherboard supports and is installed with 8GB.
And if it's Windows Vista you're using, you are only left with 3.12GB for user applications.
A 32 bit OS cannot go beyond 4GB of addressable memory.
Why? A 32-bit register means that 2^32 addresses, or 4 gigabytes worth, can be referenced. This is a hard, mathematical limitation.
This 4GB includes system memory, video RAM, and any onboard memory - anything that uses an address. This is why users see less than 4 if that's what they installed. What happens is the OS assigns addresses in order of importance: whatever's on the Motherboard, then Video, and then the installed DIMMS. What you see displayed as usable is the value of your physical RAM less Video and onboard.
You may be able to put more physical RAM on the Motherboard, but you cannot use it (unless you're using a motherpord that supports PAE (Physical Address Extension) AND tweaked your Windows to enable PAE AND USING ONLY DRIVERS THAT SUPPORT PAE- or you'll have shitloads of Blue-Screen Stop errors.
To use more than 4GB total addressable memory, you much go to a 64bit OS. That gives 2^64 (17,179,869,184 gigabytes) of addressable space.
So, Tzahi, if your Windows is a 32bit version, you're only using 4GB out of the 6GB you've got there...
