The Zone

 

If you're one of those lucky people who can afford 4GB in your computer, you might have noticed how come you only have 3GB or so and not 4GB instead.  Well the answer lies in a 32-bit (x86) processor, even if it supports 64-bit (x64), for you need n x64 operating system before you can take advantage of the x64 feature.

 

An x86 processor can only support up to 3GB or so of memory, even if it actually is supposed to support up to 4GB.  The loss of the nearly 1GB is due to other hardware in the computer which the processor must communicate with, and so this takes up the extra space which could have been given to you to get more memory.

 

The only solution is to use an x64 OS - but even then, you need x64 software to take advantage of beyond the 3GB.  So the next time you think about upgrading to 4GB of memory, if you don't have x64 software on an x64 OS, then you better just install 3GB of memory and use the extra 1GB to purchase something else instead.

 

Source : Microsoft Support