NAME
       ReadUnitID - reread and return the type of drive (V37)

   SYNOPSIS
       idtype = ReadUnitID( unitNum ), DRResource
        D0                     D0         A6

        ULONG ReadUnitID(LONG);

   FUNCTION
        Rereads the drive id for a specific unit (for handling drives
        that change ID according to what sort of disk is in them.  You
        MUST have done a getunit before calling this function!

   INPUTS
        unitNum -- a legal unit number (zero through three)

   RESULTS
        idtype -- the type of the disk drive.  Standard types are
                defined in the resource include file.

   EXCEPTIONS

   SEE ALSO
        getunitid()

   BUGS