ENVS 1500 Lecture Notes - Lecture 13: Microkernel, Message Passing, Virtual Memory
13 May 2018
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ENVS 1500 Tutorial 13 Notes – Macintosh OS X
Introduction
• The Mach operating system kernel includes message passing, interrupt processing,
virtual memory management, scheduling, and a basic set of I/O device drivers.
• It is possible to build a microkernel with nothing but message passing, interrupt
processing, and minimal memory management, although the practical advantage of
doing so has not been shown.
• The microkernel configuration constitutes a client-server system, where clients and
servers reside on the same system.
• Operating system services outside the essential functionality are performed by
programs in user mode.
• Each program acts as a server that performs specific operating system tasks upon
request of application programs as well as other operating system programs, the clients
in this model.
• Clients request services by sending messages directly to the microkernel.
• The microkernel passes the messages to the appropriate server, which performs the
required function, and replies to the request by sending a message back to the client.
• The reply is also passed through the microkernel.
• System security and integrity is maintained, because all communication must pass
through the microkernel.
• One of the advantages of the microkernel configuration is that it is possible to create
different operating system designs simply by changing the service programs that reside
outside the microkernel, while maintaining the security and stability of the microkernel.
• For example, Macintosh OS X is one of many operating systems built on the Mach
microkernel.
• The microkernel approach offers reliability, flexibility, extensibility, and portability.
• It is particularly amenable to object-oriented design.
• New features can be added easily without compromising the system.
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