The hard drive space on my Vista machine recently dropped to almost nothing, and I was really confused what was going on. I used my favorite disk space visualizer (WinDirStat). However, I couldn’t figure it out. Finally, I found that the following steps cleared it up:

1. Run Disk Cleanup (search from Start menu)

2. Choose “Files from all users on this computer”

3. When it’s done scanning (which can take forever), select the More Options tab

4. Select Cleanup under System Restore and Shadow Copies

This freed over 40 GB for me! I think that what happened is that the Zune software touched all of my media, which created shadow copies of each file, using a bunch of space. Shadow copy space must not show up for utilities like WinDirStat.

There’s a useful article on My Digital Life on how to limit how much space will be used. My was set to unbounded space.