You move the drive head to a specific track by passing an IOExtTD to the
device with TD_SEEK or ETD_SEEK set in io_Command, and io_Offset set to
the byte offset of the track to which the seek is to occur.

    DiskIO->iotd_Req.io_Offset = (ULONG)(TRACK_SIZE * track);
    DiskIO->iotd_Req.io_Command = TD_SEEK;
    DoIO((struct IORequest *)DiskIO);

   Seeking is not Reading.
   -----------------------
   TD_SEEK and ETD_SEEK do not verify their position until the next
   read. That is, they only move the heads; they do not actually read
   any data.