NAME
       AllocUnit - allocate a unit of the disk

   SYNOPSIS
       Success = AllocUnit( unitNum ), DRResource
        D0                   D0         A6

        bool allocunit(long);

   FUNCTION
        This routine allocates one of the units of the disk.  It should
        be called before trying to use the disk (via GetUnit).

        In reality, it is perfectly fine to use getunit/giveunit if allocunit
        fails.  Do NOT call freeunit if allocunit did not succeed.  this
        has been the case for all revisions of disk.resource.

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

   RESULTS
        Success -- nonzero if successful.  zero on failure.

   EXCEPTIONS

   SEE ALSO

   BUGS