NAME
        TD_GETNUMTRACKS -- return the number of tracks for the type of disk
                           drive for the unit that was opened.

   FUNCTION
        This command returns the number of tracks that are available
        on the disk unit.

   IO REQUEST INPUT
        io_Device       preset by the call to opendevice()
        io_Unit         preset by the call to opendevice()
        io_Command      TD_GETNUMTRACKS
        io_Flags        0 or IOF_QUICK

   IO REQUEST RESULT
        io_Error - 0 for success, or an error code as defined in
                   <devices/trackdisk.h>
        io_Actual - if io_Error is 0 this contains the drive type connected to
                    this unit.

   SEE ALSO
        td_getdrivetype