The functionality of the kernel is broken down into separate processes,usually called servers. Ideally,only the servers absolutelyrequiring such capabilities run in a privileged execution mode. The rest of the servers run in user-space. All the servers,though,are separated into different address spaces. Therefore,direct function invocation as in monolithic kernels is not possible. Instead, microkernels communicate via message passing: An interprocess communication (IPC) mechanism is built into the system,and the various servers communicate with and invoke “services” from each other by sending messages overthe IPC mechanism.
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