4GB freed suddenly

[vee_ess]

No, I didn't have to unmount anything to move the ISO I don't think, but I'm not quite sure I follow. My page file is at 192MB, I've never seen it higher, actually (max is at 384MB). I did clear out my history, but I hadn't surfed that much since the last time I cleared it out (about two weeks ago), but it must still be a big source of the data that's missing.

I think you are talking about Computer Management. It has a disk section for management (partitioning and formatting) and defrag. The disk management says that the partition is healthy. I don't have a quota set for any users.