When you're running Windows on a system with 4GB RAM, you might have noticed that the entire amount of RAM is not detected (it's somewhere around 3.6GB). This is because of the way HIGHMEM (4GB and up) is handled.
Fortunately, there is a way to solve the problem, allowing the full use of 4GB...

A solution to our problem is by forcibly enabling Intel's Physical Address Extension (in short, PAE). This is done by taking the following steps:

Locate the boot partition (this usually is C: but could be something else): it contains the bootloader files such as ntldr, boot.ini, etc.

Open the boot.ini file, which is in the root of that partition (e.g. c:boot.ini). Note that you might need to change  ...