IBM 5170 Technical Reference page 387

becomes necessary to modify any of the parameters, build
another parameter block and modify the address in
Disk-Pointer to point to the new block. The parameters were
established to operate both the High Capacity Diskette Drive
and the Double Sided Diskette Drive. Three of the parameters
in this table are under control of BIOS in the following
situations. The Gap Length Parameter is no longer retrieved
from the parameter block. Gap length used during diskette
read, write, and verify operations is derived from within
diskette BIOS. Gap length for format operations is still
obtained from the parameter block. Special considerations are
required for formatting operations. See the prologue of
Diskette BIOS for the required details. If a parameter block
contains a head settle time parameter value of
°
milliseconds,
and a write operation is being performed, at least 15
milliseconds of head settle time will be enforced for a High
Capacity Diskette Drive and 20 milliseconds will be enforced
for a Double Sided Diskette Drive.
If
a parameter block
contains a motor start wait parameter of less than 1 second for
a write or format operation or 625 milliseconds for a read or
verify operation, Diskette BIOS will enforce those times listed
above.
• The following procedure is used to determine the type of
media inserted in the High Capacity Diskette Drive:
1. Read Track 0, Head 0, Sector 1 to allow diskette BIOS to
establish the media/drive combination.
If
this is
successful, continue with the next step.
2. Read Track 0, Sector 15. If an error occurs, a double
sided diskette is in the drive. If a successful read occurs, a
high capacity diskette is in the drive.
3. If Step 1 fails, issue the reset function (AH=O) to diskette
BIOS and retry. If a successful read cannot be done, the
media needs to be formatted or is defective.
ROM BIOS and DOS do not provide for all functions. The
following are the allowable I/O operations with which IBM will
maintain compatibility in future systems.
Compatibility 9-9