Setup creates a hidden, system, read-only file called SETUP.LOG in your SystemRoot\REPAIR directory. This file becomes very important if you need to repair or reinstall Windows NT.
Caution Do not delete the SETUP.LOG file.
To reinstall Windows NT, the Setup program must be started again. As it did in the initial installation, Setup inspects your system's configuration and determines whether your computer has the required free disk space to install Windows NT. It also detects existing versions of Windows NT.
If your computer does not have the required free disk space, Setup gives you the option to delete the previous versions. If you select Yes, Setup uses the SETUP.LOG file to determine which files it can delete to make space on your hard disk. If SETUP.LOG is missing, no files can be deleted and you might be forced to reformat your hard disk to reinstall.