Disk Operating System (DOS)

Description, syntax and usage of the FORMAT, CHKDSK, and DISKCOPY DOS external commands.

DOS External Commands

Unlike the DOS internal commands, which are loaded into random access memory as part of COMMAND.COM each time a computer is booted, the DOS external commands are disk-bound. That means they must be fetched from disk and loaded into RAM each time they are used.

FORMAT.EXE, CHKDSK.COM, and DISKCOPY.EXE are three examples of external commands. Their syntax follows.

Prepares a diskette for use by DOS.

Syntax: FORMAT [d:]

Parameters: [d:] = Drive which is to receive the format.

Optional switches:

  • /s Include all system files necessary to make disk "bootable"
  • /b Reserve space for system files on diskette. (Formats 320k instead of 360k).
  • /v Volume label of 11 characters

Some examples:
  • To format a diskette in drive B: without system files:

  • To format a diskette in drive A: with system files:
  • FORMAT A: /s

  • To give the formatted diskette a volume name, include the /v switch:
  • FORMAT A: /V

  • Combine switches to format a boot diskette with a volume label:
  • FORMAT A: /S /V

Analyzes disk or diskette (first and only parameter) and displays disk and memory status report.

Syntax: CHKDSK [d:] [/f] [/v]

Parameters: [d:] = Drive upon which to perform CHKDSK.

Optional switches:

  • /f Fix. Writes lost clusters to a disk file and corrects file allocation table.
  • /v Verbose. Lists all files on a disk.


  • To display statistics about the diskette in drive A:
  • To display statistics about the first hard disk and fix any lost clusters:
  • CHKDSK A: /f

Makes an exact copy of a diskette, including hidden system files if they are present.

Syntax: DISKCOPY [d1:] [d2:]

Parameters:[d1:] = Drive for source diskette, [d2:] = Drive for target diskette.


  • To make an exact copy of a diskette in drive A: to a diskette in B:
  • To make an exact copy of a diskette using only drive A:

    (Change source and target diskettes as requested).
DISKCOPY asks for a SOURCE diskette (the diskette being copied) and a TARGET diskette (the diskette being copied to). The TARGET diskette need not be formatted, DOS will format it while doing the DISKCOPY. If the SOURCE diskette is bootable, the system will be transferred to the TARGET as well. The two disk drives must always use the same media.

Bruce Miller, 2018
DOS Articles Index

All Articles Index

  Hermit Homepage