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System Software

Notes
Figure 2.8: Diagram of Exokernel

In client-Server Model, all the kernel does is handle the communication between clients and
servers. By splitting the operating system up into parts, each of which only handles one fact of
the system, such as file service, process service, terminal service, or memory service, each part
becomes small and manageable; furthermore, because all the servers run as user-mode processes,
and not in kernel mode, they do not have direct access to the hardware. As a consequence, if a
bug in the file server is triggered, the file service may crash, but this will not usually bring the
whole machine down.
Another advantage of the client-server model is its adaptability to use in distributed system. If
a client communicates with a server by sending it messages, the client need not know whether
the message is handled locally in its own machine, or whether it was sent across a network to a
server on a remote machine. As far as the client is concerned, the same thing happens in both
cases: a request was sent and a reply came back.

Figure 2.9: Diagram of Client-Server Model

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