Operating Systems

Objective

The historic background What the OS means? Characteristics and types of OS General Concept of Computer

System

A Computer System consists of five components, namely,

Hardware provides the basic resources including CPU, Memory,

Harddisk, etc. Application programs

define the ways in which resources are used to solve the problems of the users

Users to use the system

OPERATING SYSTEMS (OS) to operate the system

Document

policy to guide the application

How can application programs make use of hardware resources?

How to move a program from disk to main memory?

How can a character be read in from the keyboard and is displayed on the screen?

How to control a printer for printing a file? Operating systems provide a link between

application programs and the hardware.

What Operating Systems can do? Program modules within a computer

system that govern the control of system resources

OS is a resource manager which: Keeps track of the resources Enforces policy that determines who get

what, when, and how much Allocates resources Reclaims resources

Terminology Resource

Is a commodity necessary to get work done. This includes the disk drives, CPUs, etc.

Process Is a fundamental entity that requires resources to accomplish,

basically a program in execution. Command Interpreter

It is a special process that reads commands from a terminal.. Thread

sometimes called a lightweight process (LWP). It is a basic unit of CPU utilisation

Historical Developments

Stage one The computer systems at that time were massive,

expensive and difficult to use. Stage Two, Operator-driven

In an effort to avoid idleness, an operator was hired to perform the repetitive tasks

Stage 3 Off-line Much of the operator’s job was mechanical. The

next stage was to automate that job

Historical Development. Stage Four, Spooling

At this stage, disks were introduced as a secondary storage medium.

Stage five, Multiprogramming having more than one job by partitioning the main

store into several pieces, Stage Six, Time sharing system

called multi-tasking and is a logical extension of multiprogramming.

Stage Seven, Distributed Systems The more recent development focuses on

distributed computing.

Spooling

Multiprogramming

Time sharing

Structure of Operating systems There are four different structures

as given below: Monolithic system Layered System Virtual Machine Client-server model

OS Components

Process Management Memory Management Secondary Storage Management I/O System Protection System Command Interpreter System

Monolithic

Layered

Virtual Machine

Client-server

Future trend Multiprocessing will become much more common. Hardware architectures of the future will distribute

control into localized processors. Languages are being developed to exploit

concurrency Massive parallelism will become common will be designed to foster (foster means help) the

operation of virtual machines Developments in software engineering will result

in more maintainable

Classification of Operating System Off-line, Batch and Remote batch On -line, Time sharing Personal computing, User

progammable Data base, Real time Non-programmable, Multi-user single user, System features

Characteristics of OS

Have priority over user programs Manage input, output, memory and

CPU (Data entry, output to printer) Increase computer system

efficiency Sequence and schedule programs Handle hardware errors and

pProvide security for user programs

Windows 95/98 - Outline

Win95 was released in August 1995

Total rewrite and replacement for Windows 3.x

Windows-95 “backwards compatible” with software from earlier O/S

Major, modern features include

Summary Compatibility

It means that the ideal operating system is designed to provide execution environments for applications for other operating systems.

Portability It means that the operating system can be ported to a variety of

different machines Robustness

It means that the ideal operating system can provide protection from accidental or deliberate damage by user programme

Usability Easy to use, click and drag are more friendly than DOS prompt

commands

Summary Efficiency

The system functions quickly, makes optimum use of the resources Flexibility

Adaptability to a specific environment, like Unix can be in Minicomputer or PC

Transparency Users are unaware of all details they need not know

Security Protecting data from unauthorized access

Integrity Protecting itself and users from damage or any other ill effect of

other’s error or malice.