[PC] [XT] [AT]
Expects: AH    05H
CX    track (cylinder) number in the high 10 bits (see below)
DL    drive: 0-3=diskette; 80H-81H=hard disk
DH    head number
ES:BX addr of buffer containing formatting info (see notes)
                                                                  
Returns: AH    BIOS disk error code if CF is set to CY
                                                                  
Info: This formats a single track on one head of a diskette or hard
disk.  Any existing data on that track is destroyed.

CX Bits 6-7 of CL are the high two bits of the 10-bit value whose
low 8 bits are in CH.  See INT 13H 02H for details.

ES:BX The layout of the data ate ES:BX varies by drive type and BIOS:

PC (and all diskette operations)
ES:BX points to a series of 4-byte values, one for each sector on
the track.  The layout is 'CHSL':

Offset Size Contents
                                                                 
+0     1   bCylinder   track number: 0-n
+1     1   bHead       head number: 0-n
+2     1   bSector     sector number: 1-n
+3     1   bLenCode    0=128, 1=125, 2=512, 3=1024

There is one of these 4-byte structures for each sector on the
track (for instance, 36 bytes for a 9-sector-per-track diskette).
Interleave is set up by organizing them non-sequentially (e.g.,
1,5,2,6,3,7,4,8)

AT (and all modern hard disk drives and BIOSes)
ES:BX points to a series of 2-byte values, one for each sector on
the track.  The layout is 'FS':

Offset Size Contents
                                                                 
+0     1   bFlag       00=good, 80=bad/unusable
+1     1   bSector     head number: 0-n
2               length of one record

There is one of these 2-byte structures for each sector on the
track (for instance, 110 bytes for a 55-sector-per-track hard
disk).  Interleave is set up by organizing them non-sequentially.

XT (very old XT BIOSes only)
ES:BX is not used; instead AL contains an interleave value
between 1 and 16.

See Also: DOS fn 440dH 42H (IOCTL format track)
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INT 13H 05H: Format Track