When a Windows PC reaches less than 10 percent (or 100MB) of free disk space, it can waste a lot of time trying to use the relatively small amount of empty territory. Worst of all, you can get mysterious lockups or strange error messages. To quickly check how much space you have left on a drive or a partition, right-click on the drive icon and select Properties. Or, if you have a system utility installed, click on its icon in the Windows Taskbar. If you have less than 100MB of free space left, move seldom-used files and programs to removable media, dump items you never use in the Recycle Bin (and don't forget to empty it), or--better yet--upgrade to a bigger, faster hard drive.