I have installed a pair of DDR2 PC2-6400 2Gb modules into my Toshiba Satellite Pro 300 running Win xpPro Sp 3 32bit.

When I do a scan using the "Crucial" website scanner it shows I have 4Gb of RAM installed, yet when I check on the "system" on the Xp control panel it only shows 2.99Gb ?? The Crucial site says that Xp Pro sp3 32bit will work and use upto 4Gb So where has 1Gb dissapeared to???

nigel, October 2011

Some of that memory is mapped to your video card.
Some more is mapped to the various I/O devices, like the USB and sound adaptors, as well as the keyboard.
Then, there is the ROM of the BIOS.

It all ads up to roughly 1 Gb, the video part been, by far, the bigest contributor.

Unless you have a 64 bits CPU and a 64 bits OS, you can't use that part. The CPU, OS and drivers DO use it, but the applications can't.

Electro, October 2011