I occasionally run Windows' Disk Cleanup to purge cruft
left over from updates. I started it today and it reported
that it could liberate 21GB! on C:. The list of files to
delete included an entry I'd never seen befo "Compress
your OS drive" (20GB), but that entry was NOT checked so
would be skipped if I pressed OK. Is Cleanup proposing to
actually compress the drive or is there a hulking file
somewhere that it concludes I don't need?