Page "Microkernel" Paragraph 36

A key component of a microkernel is a good IPC system and virtual-memory-manager design that allows implementing page-fault handling and swapping in usermode servers in a safe way.

Since all services are performed by usermode programs, efficient means of communication between programs are essential, far more so than in monolithic kernels.

The design of the IPC system makes or breaks a microkernel.

To be effective, the IPC system must not only have low overhead, but also interact well with CPU scheduling.