Page 24 - DCAP403_Operating System

Unit 2: Operation and Function of Operating System

Protection Notes

The various processes in an operating system must be protected from each other’s activities. For

that purpose, various mechanisms which can be used to ensure that the files, memory segment,
CPU and other resources can be operated on only by those processes that have gained proper
authorisation from the operating system.

Example: Memory addressing hardware ensures that a process can only execute within
its own address space. The timer ensures that no process can gain control of the CPU without
relinquishing it. Finally, no process is allowed to do its own I/O, to protect the integrity of
the various peripheral devices. Protection refers to a mechanism for controlling the access of

programs, processes, or users to the resources defined by a computer controls to be imposed,
together with some means of enforcement.
Protection can improve reliability by detecting latent errors at the interfaces between component
subsystems. Early detection of interface errors can often prevent contamination of a healthy
subsystem by a subsystem that is malfunctioning. An unprotected resource cannot defend
against use (or misuse) by an unauthorised or incompetent user.

Task “Memory is the most expensive part of system.” Discuss.

Networking

A distributed system is a collection of processors that do not share memory or a clock. Instead, each
processor has its own local memory, and the processors communicate with each other through
various communication lines, such as high speed buses or telephone lines. Distributed systems
vary in size and function. They may involve microprocessors, workstations, minicomputers, and
large general purpose computer systems.

The processors in the system are connected through a communication network, which can be

configured in the number of different ways. The network may be fully or partially connected.
The communication network design must consider routing and connection strategies and the
problems of connection and security.
A distributed system provides the user with access to the various resources the system maintains.
Access to a shared resource allows computation speed-up, data availability, and reliability.

Command Interpretation

One of the most important components of an operating system is its command interpreter. The
command interpreter is the primary interface between the user and the rest of the system.
Many commands are given to the operating system by control statements. When a new job is
started in a batch system or when a user logs-in to a time-shared system, a program which reads
and interprets control statements is automatically executed. This program is variously called
(1) the control card interpreter, (2) the command line interpreter, (3) the shell (in Unix), and so on.
Its function is quite simple: get the next command statement, and execute it.
The command statements themselves deal with process management, I/O handling, secondary

storage management, main memory management, file system access, protection, and
networking.

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