I guess you could take a view by simply looking at
System -> System Info -> Summary within XBMC. This will tell you how much RAM you're using.
If it helps, my Revo 3600 is reporting as 2771MB total, 2551MB free - that's with 4Gb on board. Acer explain where the RAM has gone to on
this site. It's not that the Atom can't address the full 4GB, it's just that the architecture of the box eats it:
Quote:256 megabytes (MB) is assigned as video memory (I have this set to 512MB in the BIOS - certainly one advantage of more RAM).
A total of 512 MB is used for PCI hardware resources.
256 MB is dedicated to PCI Express hardware resources.
... so that's 1.25GB gone, 2.75 left, give or take a bit. And XBMC and the OS is taking up a whole 220MB when it's not playing anything (Confluence skin, XBMC PVR pre-11) - bear in mind the OS, though, and how memory is used and how swap typically reflects RAM. On my system, that figure goes up by about 120MB when I'm playing a 1080p h.264 file at 2.5Mb/s, so still within the 2Gb I had originally.
You could always open a shell and use
top or similar to measure whether it's the CPU or memory that's slowing you down. I originally upgraded to try to get Vista to work properly before I gave up on the concept of "properly" and deleted it - not sure if I'd bother now.
Mind you, my CPU(s) hardly break sweat either because of the VDPAU acceleration. I love my little ION box!