G'Day,
Generally this can be seen in the
BIOS, especially if you have 'on-board' graphics.
For example...if there is
1024MB RAM installed, and the graphics use
64MB RAM; then, the available RAM will be
960MB RAM.
If you want to determine this, you can go
here, and download a
freeware program called Everest™ Home Edition.
(Click on the coloured link.)
Post back with any other queries/concerns.
Kind Regards,