I have recently upgraded (he he) back to xp from vista and i recognised that xp only sees 3.2 gb of ram in my system when i have 4.0gb in the bios it shows up but not xp any suggestions why not.? cheers
That's because you have a 32bit version of XP. 32bit versions can only recognize up to 3-3.5GB of RAM (including your videocard RAM). 64bit OS's, on the other hand, can recognize above 4GB.
32 bit operating systems like xp, Linux, and some versions of vista can only use about 3.5 gb of memory(ram+video card).To use 4gb of ram you would need a 64bit operating system like Vista 64bit.
It's because windows can only address up to 4GB (2^32bits = 4GB) ram, but some of this address space is needed for hardware. The more peripherals you have, the less it will be able to use as RAM.
I'm not sure the PAE switch allows you to use the WHOLE 4GB, but it should allow you to use more than you can currently. It's been a while since I ran 4GB, I don't really remember