When you run Disk Cleanup, one of the categories of files available is "Compress Old Files." From the description of these files you would presume that it is not safe to actually remove them (as they may be programs of data that you may need in the future), but the fact that they are presented during Disk Cleanup leads one to suspect that they could/should be deleted.

1. Can these files safely be deleted?
2. Is there a way to determine just which files will be deleted?

The "compress old files" feature allows you to squeeze down the size of files on your hard disk so they'll take up less space. Any file on the disk that is older than a specified age is compressed. Note that you can still open these files. They aren't removed from the disk. Windows XP does not "zip" these files. It uses NTFS compression, which compressed each cluster within a file individually. To use it, the drive needs to be formatted with NTFS. You won't even know that the file is compressed unless Windows Explorer is configured to show compressed files in a different color.

Here's how you change the age files need to be before Disk Cleanup compresses them:

1. Click Start, point to All Programs, point to Accessories and then point to System Tools. Click Disk Cleanup.
2. A Disk Cleanup dialog box will appears. Select the drive you want to clean up and click OK.
3. In the Disk Cleanup for dialog box, click on the Compress old files entry, then click the Options button.
4. You can change the number of day in the Compress Old Files dialog box. Sixty days is a good round number. Click OK.
5. Click OK in the Disk Cleanup dialog box.

Disk Cleanup is designed to mark the following types of files for removal: temporary Internet files, downloaded program files (such as ActiveX controls and Java applets), Windows temp files, Windows components that aren't being used and installed programs that aren't being used. It's usually safe to remove these. In the Files to Delete box on the Disk Cleanup tab of the Disk Cleanup applet, you'll see a list of the types of files recommended to be deleted. For example, if Disk Cleanup lists "Office Setup files," these are the files used to install Office. Removing them won't harm your program, but if you do a repair or patch operation, you might have to insert the Office installation CD. On the More Options tab, if you click the Clean up button for Windows components or Installed Programs, you'll be shown a list where you can check or uncheck boxes to indicate which components or programs you want to remove.