This is an extract of an article in Dr. Dobb's, April 1981.

     This program requires a Z80 MPU, at least 32K byte RAM memory, two
flexible disk drives and CP/M 2.x.

     All console I/O is done using the standard CP/M function calls.
For maximum test speed, access to protected system areas and to avoid
error interception by CP/M, disk I/O is performed directly by calls to
the BIOS drivers.

     The program is configured to test a soft sectored, double density,
double-sided 8" disk with 154 tracks (77 per side), 52 records per track
(26 for single density) and 128 byte sectors.  If using a different type
of disk drive, the number of tracks and/or records per track may be
specified during the initialization dialog, or the program may be reas-
sembled to modify the default configuration.

     The program does not exhaustively check out the drive.  Any errors
detected by the program must be interpreted with care.	Intermittent
errors occurring throughout a broad range of disk addresses probably
indicates a problem with the disk drive unit.  Errors indicated at con-
sistent addresses within adjacent tracks may result from worn or damaged
disk.  Error-free execution of the test certainly indicates an intact
and useable diskette.

     NOTE:  the program is rather insensitive to drive problems related
to head movement since the diskette is addressed in a smooth sequential
manner.

     ERROR LISTING

     Errors detected by the program may be itemized on the system con-
sole or the line printer.  The pass, drive name, track and sector where
the error occurred are listed.	All numbers are in decimal.  The error
type is designated at the right.  In the explanations below, 'hardware
error'signifies an error status code passed from the low-level disk
driver and usually means a CRC fault or seek incomplete.

     The program may be aborted at any time via a CTL-C.
	

ERROR TYPE		      EXPLANATION
============================================================
read error - original data    If running in restore  mode,
			      hardware read error noted as
			      the original data was being
			      loaded into memory.

write error - test data       Hardware error noted as the
			      test data pattern was being
			      written on the diskette.

read error - test data	      Hardware error noted as the
			      test data pattern was being
			      read back from the diskette.

compare error - test data     Difference was found between
			      the data pattern that was
			      written to the diskette and
			      the data that was read back.

write error - restore phase   Hardware error noted as the
			      original data was being
			      written back to the diskette.

read error - restore phase    Hardware error noted as the
			      restored original data was
			      being read back for verification.

data cannot be restored       Compare error found between
			      the original data rewritten to
			      the diskette and the same
			      sectors read back for verification.