INT 13h,  0Bh (11)       Write Long                               diagnostics

    Writes one or more long sectors to a fixed disk from memory. A long
    sector is a sector of information plus 4 bytes representing the ECC
    code for the sector. This service can be performed on fixed disks
    only.

       On entry:      AH         0Bh
                      AL         Number of sectors to write (1-127)
                      CH         Cylinder number (10-bit value; upper 2 bits
                                 in CL)
                      CL         Starting sector number
                      DH         Head number
                      DL         Drive number (Bit 7 must be set)
                      ES:BX      Address of memory buffer

       Returns:       AH         Status of operation (See Service 01h)
                      AL         Number of sectors written
                      CF         Set if error, else cleared

    Writes the information at a memory buffer to the sectors starting at
    the specified location (head, cylinder, and track)

       Notes:         This service is for diagnostics only. For a more
                      generalized version, see Service 03h, which writes
                      sectors for both diskettes and fixed disks. Also see
                      INT 26h (DOS), which  allows the writing of absolute
                      sectors from any type of block device.

                      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.

                      The value returned in AL (number of sectors written)
                      may not give the correct number of sectors, even
                      though no writing error has occurred. Use the
                      results of the Carry flag and AH (status flag) to
                      determine the status of the operation.

                      The number of sectors to write (AL) can be 127
                      sectors at most.

                      If an error is encountered while writing a sector,
                      use Service 0h to reset the drive and retry the
                      operation. It is recommended that at least 3 retries
                      be attempted before an error is signalled, since the
                      error may have resulted from the diskette motor not
                      being up to speed.

                      Because of the architecture of the DMA channel, an
                      error will occur if the buffer in memory for the
                      sectors overlaps a 64K page boundary. A 64K page
                      boundary is a memory location which is one of the
                      following (10000h, 20000h, 30000h, etc.). Ensure
                      that no part of your buffer falls on such a
                      boundary. If it does, then create a new buffer or
                      start the buffer just after the boundary.

                      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.