why isn't my computer using all my memory?

Yes, I've seen that a thousand times. Your system is using "integrated" video which shares memory with RAM. Upgrade to a standalone video card with dedicated memory for better performance (and to free up the 128MB that you have missing).

When you first turn the PC on, enter the BIOS. You can usually see how much is being used and even adjust it. Typically, you want to leave it at the default setting until you upgrade to a video card.

Sounds like your system may be allocating some memory to the graphics card. This is pretty common in low-end notebooks that have integrated graphics.

If this is a notebook then you're not going to be able to add a video card so your other option is to add more RAM or if it is a vista machine you can even use a USB 2.0 flash drive to provide additional memory to the system.

Take it easy - the reason it says 894 is that some of your memory is shared with onboard video graphic.

some of that memory is to run your operating system vista is a bigger file than xp

because you haven't run any program or game yet in your pc, try to play a game, or program, then pause it and then minimize it then alt ctrl del you should see in the task manager how much memory your pc is using

SOME OF YOUR MEMORY IS BEING USED TO RUN YOUR SYSTEM.SO IT WILL SHOW AVAILABLE RAM ONLY