Backing up onto a disk with files
Unless you use the /a switch, backup deletes old files (including read-only files) from a backup disk before
adding new files to it.
Backup log file
If you use the /l switch and do not specify a name and location for the log file, the backup command adds a file named BACKUP.LOG to the root directory of the source
drive. If the BACKUP.LOG file already exists, backup adds the current entry to the file. A backup log-file entry uses the
The date and time of the backup appear on the first line.
Each filename appears on a separate line with the number of the backup disk
that contains the file.
The backup log file can assist you later, when you need to identify the files
you want to restore. The restore command always returns a file to the original directory or subdirectory
recorded in the backup log, creating the subdirectory if necessary.
Labeling backup disks
It is important to label and number backup disks consecutively. As each disk
is filled, backup prompts you for the next disk. When you restore files, you need to insert the
backup disks into the disk drive in the same sequence. To check the sequence
of backup disks (MS-DOS version 3.3 or later), use the dir command to check the disk number.
Backup and system files
The backup command cannot back up the system files IO.SYS, MSDOS.SYS, and CMD.EXE. You
can use the sys command to copy these files onto a floppy disk.
Using an old version of the restore command
You cannot use an old version of the restore command (MS-DOS version 3.2 or earlier) for files backed up with MS-DOS
version 3.3 or later. If you attempt this, Windows NT displays the following
Source does not contain backup files
This error occurs because the format of old backup files differs from the
format of files backed up with MS-DOS versions 3.3 and later.
Backup exit codes
The following list shows each exit code and given a brief description of its