Donet

When I start FSX SE with the FSUIPC log tape running at the top of the screen I start of with a reading of around 1911800. After flying for a while it drops down to 1500000 and in heavy scenery areas like Seatle in Orbx Pacific NW it drops to 600000. My question is what do these numbers represent.. Is it VAS memory and are they bytes or megabytes or what? As you can see I'm not a computer guru but I'd like to know so that I can see how they might relate to numbers I see in Task manager