another feature of the -rt mode is the memory locking ... it's enabled on machines, where _POSIX_MEMLOCK is defined (at least on linux it is). this will force the memory to be represented in the physical memory. (one will not be able to allocate more memory).
actually i think they should be two separate features :
the real-time priority ( -rt )
and the memory locking ( -ml ? )
cause you might want a high priority without the memory limitation.
cheers, sevy