The key features are isolation and fault management. Isolation means that each process is separated from the others and can only communicate via a safe means. W

The key features are isolation and fault management. Isolation means that each process is separated from the others and can only communicate via a safe means. What happens when a process dies? Good systems have far more fault-tolerance. An additional benefit is security. Your model can rely on some processes having the capability to access confidential data. These act as proxies for accessing that data and protects it. The OpenBSD operating system has used this "privilege separation" trick for years. Everything with shared memory will die in the long run. The hardware can't keep on fooling us with a big memory space shared among all processes anyway.