VERDISK is a quick way to check on the condition of disks, to
give warning of impending failure.

	It uses the PC disk I/O call (INT 13) to verify the readability of
each sector on the disk.  All verify errors are reported, indicating the
error type (drive seek, controller, CRC, missing sector, missing addr mark),
the side, track and sector, and the number of unsuccessful retries, up
to a maximum of 5.  The batch ERRORLEVEL is also set as a return code.

	All PC and AT  5.25" floppy formats and IBM hard disks are
supported.  The IBM 8" floppy formats are not supported.  If you have
hard disks then DOS device B: must be BIOS unit 80H, C: must be 81H,
and so on.

Syntax:  VERDISK d:

Where d: is the drive specifier.

The ERRORLEVEL is OR'ed with    to indicate
  1        recoverable disk error (successful retry)
  2        non-recoverable error (unsuccessful after 5 retries)
  4        non-supported disk type
  8        invalid drive spec