> Since inter-process communication in Amiga OS was based on message passing with memory-sharing, it was impossible to add MMU-based memory protection later. W

> Since inter-process communication in Amiga OS was based on message passing with memory-sharing, it was impossible to add MMU-based memory protection later. Why can't you do shared memory message passing with MMU protection? There is no reason an application in a modern memory protected OS can't voluntarily share pages when the use case is appropriate. This happens today. You can mmap the same pages, you can use posix shm, X has the shm extension...