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Int 13h, 0Ch            Seek to Cylinder                           fixed disk

    Positions the read/write heads over a specified cylinder for a
    fixed disk. This service can be performed on fixed disks only.

        Entry   AH = 0Ch
                CH = Cylinder number (10-bit value; upper 2 bits in CL)
                DH = Head number
                DL = Drive number (Bit 7 must be set)

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

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

    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.

    Even though the head value is not needed, you must supply a legal
    value--or else the seek will not be performed and an error will be
    returned.

    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.