I suspect something strange about my disk usage. I had 9GB of free space on my primary partition and then after two days suddenly I had 16GB free. I had not since installed, deleted, or downloaded anything. This has repeated several times; free space on my primary partition (C:) seems to rise and fall by itself. Can someone explain where this might be coming from? I am using Windows 7 x64.
This is not so much a problem but could be being caused by System Restore creating new restore points and deleting old restore points.
The creation of a restore point is done automatically every few days, I would expect the check for and deletion of old restore points to happen on a similar time frame.
Creating a restore point would block off some space while deletion would free it up again.
Restore points (also known as shadow copies) allow you to use Previous Versions, which is a useful feature if you accidentally delete a file, and also allow you to restore your system to a previous "known good" working state.