This structure is used in the following IOCTL fns:
    440dH 41H (write track on logical drive)
    440dH 61H (read track on logical drive)

    DvRq 13H  (generic IOCTL for block devices)

  Offset Size Contents
  ▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
    +0     1  rSpclFns     (always 00)
    +1     2  wHead        head to read/write
    +3     2  wTrack       track (cylinder) to read/write
    +5     2  wStartSect   starting sector (0-based; sector 1=0, 2=1...)
    +7     2  wSectCnt     sector count (0-based; use 8 for 9-sector track)
    +9     4  fpBuff       32-bit addr of buffer containing data to write
                           (440dH 41H) or addr to hold data read (440dH 41H)
          0dH (13)         size of an IoctlRdWrtTrackRec

   Notes: The wStartSect field is relative to the start of the track (for
          instance, to write an entire track on a 9-sector/track diskette,
          set wStartSect to 0 and set wSectCnt to 9.

          This is the only place I've seen where tracks are not specified
          with their "hardware code" numbers (e.g. 1-9).

See Also: fn 440dH (Generic IOCTL for block devices)
          Device Drivers
          DOS Functions