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Int 13h, 05h            Format Cylinder                                   all

    Initializes each sector on a specified cylinder with sector
    address and size information.

        Entry   AH    = 05h
                AL    = Number of sectors to format (diskette) or
                      = Interleave (XT)
                CH    = Cylinder number (10-bit value; upper 2 bits in CL)
                DH    = Head number
                DL    = Drive number
                ES:BX = Pointer to address field list (See below)

        Return  AH = Status of operation (See Service 01h)
                CF   Set if error, cleared otherwise

    ------------------------------------------------------------------

    Note
    Values in DL less than 80h specify floppy disks; values from 80h
    to 87h specify fixed disks.

    The cylinder number is a ten-bit quantity (0 through 1023). Its
    most significant two bits are in bits 7 and 6 of CL; the remaining
    eight bits are in CH. The starting sector number fits in the
    low-order portion (lower 6 bits) of CL.

    If an error is encountered, use Service 0h to reset the drive and
    retry the operation.

    For the AT, XT-286, and PC Convertible, the BIOS executes Int 15h,
    Service 90h (Device Busy), for the diskette (Type = 01h) and the
    fixed disk (Type = 00h) prior to waiting for the interrupt. Int
    15h, Service 91h (Interrupt Complete), is executed upon
    completion. Also diskette operations that require the diskette
    motor to be on will call Int 15h, Service 90 (Device Busy), with
    the type equal to "Diskette Drive Motor Start" (Type = FDh). This
    allows the system to perform another task while the drive motor is
    waiting to get up to speed.


    Interleave        "Interleaving" is the process of putting
                      logically contiguous sectors in physically
                      noncontiguous locations, in order to to increase
                      disk performance. Below is outlined the
                      different ways of changing the interleave factor
                      depending on the type of media (fixed disk or
                      diskette) and the machine type.

                      The pointer to the address field list (ES:BX)
                      varies depending on what type of machine and
                      type of disk (fixed or diskette) the formatting
                      process will occur on. Also the interleave
                      factor is specified differently for the
                      different machines and disk types. Below are the
                      formats for the different types of machines and
                      disks.

    Diskette          ES:BX points to a list of address marks for each
                      sector on the track to be formatted. Each
                      address mark consists of 4 bytes. Therefore, to
                      format a 9- sector track, the list MUST consist
                      of 36 bytes (4 * 9). The 4 bytes making up the
                      address mark are defined as follows:

                          Byte 1 - Cylinder number (C)
                          Byte 2 - Head number (H)
                          Byte 3 - Sector number (R), or Record number
                          Byte 4 - Sector Size (N)
                                      0 - 128 bytes per sector
                                      1 - 256 bytes per sector
                                      2 - 512 bytes per sector
                                      3 - 1024 bytes per sector

                      Note that you can change the interleave factor
                      by specifying byte 3 (sector number) in a non-
                      sequential order.

                      Standard MS-DOS diskettes are formatted with 512
                      bytes per sector (N=2) and with no interleave.
                      Thus, the address field list for a standard
                      MS-DOS nine- sector track would look like this:

                             C H R N    C H R N    C H R N ... C H R N
                             0 1 1 2    0 1 2 2    0 1 3 2     0 1 9 2

                      Before formatting a diskette, if there is more
                      than one type of diskette supported by the
                      drive, you will need to call Service 17h (Set
                      DASD Type for Format) or Service 18h (Set Media
                      Type for Format). If these services are not
                      called, Service 05h will format the disk using
                      the maximum disk type supported by the disk
                      drive. Older machines that don't support Service
                      17h (Set DASD Type for Format) or Service 18h
                      (Set Media Type for Format) may have to directly
                      modify the Diskette Drive Parameter Table. This
                      table is pointed to by Int 1Eh. If modifications
                      are made to the Diskette Parameter Table, make
                      sure the original values are restored.

    XT                The XT uses the AL register to specify the
                      interleave factor. The pointer ES:BX is not
                      needed for the XT.

    AT and XT-286     These machines use an address table (pointed to
                      by ES:BX), similar to the one used in diskette
                      mode but with a slight variation. The buffer
                      must be 512 bytes long. The first 2 * (sectors
                      per track) bytes contain information for each
                      sector on the track. For each sector, there are
                      2 bytes in the table. These 2 bytes are defined
                      as follows:

                            Byte 1 - Sector Format state (F)
                                      00h - Good sector
                                      80h - Bad sector
                            Byte 2 - Sector number (N)

                      For example, the following table is used to format a
                      track for a fixed disk with 17 sectors per track and
                      an interleave factor of 3.

           db    00h, 01h, 00h, 07h, 00h, 0Dh, 00h, 02h, 00h, 08h, 00h, 0Eh
           db    00h, 03h, 00h, 09h, 00h, 0Fh, 00h, 04h, 00h, 0Ah, 00h, 10h
           db    00h, 05h, 00h, 0Bh, 00h, 11h, 00h, 06h, 00h, 0Ch