In a 32-bit version of Windows, users will not be able to install and use more than about 3GB of memory. Though many 32-bit versions of Windows list a 4GB maximum memory, they are not able to address anything more than 3GB. This is due, in part, to the way your system sets up memory addresses in your computer.
A 32-bit processor is programmed to use 32 bits (hence the name) to locate each byte of memory. To determine how many addresses this gives us, we would need to take 2 (each bit can be either 0 or 1) to the 32nd power. So 2^32= 4,200,000,000. This means that each memory address 32 bits long can only refer to a location within this number (4.2 billion, or 4GB). Because your computer uses these memory addresses to locate all peripherals in the machine, it cannot address 4GB of memory even if it is installed
This means that if you would like to use more than 3GB of memory, you would need to have a 64-bit Operating system. It is fairly easy to tell which version of Windows you have. You can check this by clicking on the Start button and going to Control Panel. Once in the Control Panel, click on the System icon.
On the General tab, next to Windows XP, it will say x64 if you have a 64-bit version of the OS.
Click View and Print Details. In the System section, it will show the version of the OS under System Type. If your machine is capable of running a 64-bit OS, but is not running one, it will tell you.
Under Windows edition, it will tell you if you have a 64-bit version.
Note: If you would like to install a 64-bit version of Windows, please check with your system manufacturer to ensure that you have a 64-bit processor as 32-bit processors are not able to run a 64-bit OS.