I just did a full backup of my Vista RTM to an USB disk.

Before starting the backup I cleaned up unnecessary files and
'cleaned' th ehibernation file to reduce size.

Drive C then still contained about 60 GB of files (little or no data
files: those are stored on another drive, I backed up C: only).


Because backup finished surprisingly fast, I took a look at the backup
files afterward: there's only 15 GB. How come it's only 1/4 of the
contents of my C drive?