Q. Why does a partition show much more disk space used than the size of the files that are contained on the partition?

A. I was looking at a virtual machine and it showed 38 GB of space used on the C drive. When I looked at all the folders on the drive, however, I could only account for 16 GB of disk space. I was looking at hidden files, everything. So what was the other 22GB of space?

After some investigation I found that system protection was enabled, which, once a day and before system events such as installing a program, takes a snapshot of the file system. System protection uses up to 15 percent of the space on a disk, by default, saving snapshots that can be used for restoration purposes, and these snapshots added up to a lot of disk space.

I reclaimed my space by turning off system protection, because I never used system restore anyway. Obviously, you need to be careful of this approach if you use system protection, as this will wipe out all those restore points. To turn off system protection, open the System applet in Control Panel and click the System Protection link. You can enable and disable system protection on each disk, and if you disable system protection all system restore points for that drive are deleted.

Your other option is run the Disk Cleanup utility, which doesn't require you to turn off system restore. The utility is located in the Start menu under System Tools in the Accessories folder. Choose to clean up files for all users of the computer and then select the More Options tab, which gives the option to delete system restore and shadow copies other than the most recent restore point, as shown here.

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