The Hermit Hermit's Free Library  MS-DOS

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

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:
Some examples:


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:



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.


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.