Page 43 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes The computer networks used in these applications consist of a collection of processors that do
not share memory or a clock. Instead, each processor has its own local memory. The processors
communicate with one another through various communication lines, such as high-speed buses or
telephone lines. These systems are usually referred to as loosely coupled systems (or distributed
systems). Some operating systems have taken the concept of networks and distributed systems
further than the notion of providing network connectivity. A network operating system is an
operating system that provides features such as file sharing across the network, and that includes
a communication scheme that allows different processes on different computers to exchange
messages. A computer running a network operating system acts autonomously from all other
computers on the network, although it is aware of the network and is able to communicate with
other networked computers. A distributed operating system is a less autonomous environment:
The different operating systems communicate closely enough to provide the illusion that only
a single operating system controls the network. We cover computer networks and distributed
systems in units coming up.

Distinguish between the client-server and peer-to-peer models of distributed
system.

V Distributed Operating Systems

he V operating system is a microkernel operating system that was developed by
faculty and students in the Distributed Systems Group at Stanford University in the
T1980s. V was the successor to the Thoth and Verax operating systems.

The key concepts in V are multithreading and synchronous message passing. Communication
between threads in V uses synchronous message passing, with short, fixed-length messages
that can include access rights for the receiver to read or write part of the sender’s address
space before replying. The same message-passing interface is used both between threads
within one process, between threads of different processes within one machine, and between
threads on different machines connected by a local Ethernet. A thread receiving a message
is not required to reply to it before receiving other messages; this distinguishes the model
from Ada rendezvous.
One common pattern for using the messaging facility is for clients to send messages to
a server requesting some form of service. From the client side, this looks much like RPC
(remote procedure call). The convenience of an automatic stub generator is lacking, but on
the other hand, the client can pass one parameter by reference, which is not possible with
RPC. From the server side the model differs more from RPC, as by default all client requests
are multiplexed onto one server thread. The server is free to explicitly fork threads to handle
client requests in parallel, however; if this is done, the server-side model is much like RPC too.

Questions:
1. Differentiate between V distributed operating system and distributed operating system.

2. Define remote procedure call.

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