believe your BIOS Post screen... its the first screen you see when you powerup. looks like Dos with a bunch of system info. may disapear quickly... but it shows you specs such as total system Ram.
you could even go into BIOS and disable quick boot... then the next time it boots up, it will scan your system Ram to do a quick check for errors... at witch time it finishes it will be obviouse how much ram it shows.