The 001 file extension can be used to indicate backups or archives from many programs, including the popular application Norton Ghost. These files are often part of a backup or an archive that has been split in to multiple files due to the 2GB limit that is present on the FAT file system. In the case of Norton Ghost, these files are packaged with a GHO file which describes how to put the files together and which files are needed for the full archive to be pieced together.