You should back up data on your hard disk(s) that are not available anywhere else. For example, you might not want to back up Windows-based application programs, because you can reinstall them. However, it might be faster to restore the application programs from a backup tape rather than reinstall them if you have to replace a disk.
You can use the Windows NT backup program, Ntbackup.exe, to back up the data to a cartridge tape. You can also back up to another computer, such as a file server or the disk on a computer that is shared by other users. If you back up to another computer, you should have your files included in the backup procedure for that computer.