I don't know about the others, but at least both QNX and Minix3 cheated a little, i.e. allowing servers to write directly to other user space programs. Also, t

I don't know about the others, but at least both QNX and Minix3 cheated a little, i.e. allowing servers to write directly to other user space programs. Also, the presence of microkernel+multiserver systems is still quite symbolic in comparison with the monolithic couterparts.