Operating Systems

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

A Computer System consists of five components, namely, n Hardware u provides the basic resources including CPU, Memory, Harddisk, etc. n Application programs u define the ways in which resources are used to solve the problems of the users n Users u to use the system n OPERATING SYSTEMS (OS) u to operate the system n Document

policy to guide the application n How can application programs make use of hardware resources? n How to move a program from disk to main memory? n How can a character be read in from the keyboard and is displayed on the screen? n How to control a printer for printing a file? n Operating systems provide a link between application programs and the hardware.

What Operating Systems can do? n Program modules within a computer system that govern the control of system resources n OS is a resource manager which: u Keeps track of the resources u Enforces policy that determines who get what, when, and how much u Allocates resources u Reclaims resources

Terminology n Resource u Is a commodity necessary to get work done. This includes the disk drives, CPUs, etc. n Process u Is a fundamental entity that requires resources to accomplish, basically a program in execution. n Command Interpreter u It is a special process that reads commands from a terminal.. n Thread u sometimes called a lightweight process (LWP). It is a basic unit of CPU utilisation

Historical Developments n Stage one u The computer systems at that time were massive, expensive and difficult to use. n Stage Two, Operator-driven u In an effort to avoid idleness, an operator was hired to perform the repetitive tasks n Stage 3 Off-line u Much of the operator’s job was mechanical. The next stage was to automate that job

Historical Development. n Stage Four, Spooling u At this stage, disks were introduced as a secondary storage medium. n Stage five, Multiprogramming u having more than one job by partitioning the main store into several pieces, n Stage Six, Time sharing system u called multi-tasking and is a logical extension of multiprogramming. n Stage Seven, Distributed Systems u The more recent development focuses on distributed computing.

Spooling

Multiprogramming

Time sharing

Structure of Operating systems n There are four different structures as given below: n Monolithic system n Layered System n Virtual Machine n Client-server model

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

Monolithic

Layered

Virtual Machine

Client-server

Future trend n Multiprocessing will become much more common. n Hardware architectures of the future will distribute control into localized processors. n Languages are being developed to exploit concurrency n Massive parallelism will become common n will be designed to foster (foster means help) the operation of virtual machines n Developments in software engineering will result in more maintainable

Classification of Operating System n Off-line, Batch and Remote batch n On -line, Time sharing n Personal computing, User progammable n Data base, Real time n Non-programmable, Multi-user n single user, System features

Characteristics of OS n Have priority over user programs n Manage input, output, memory and CPU (Data entry, output to printer) n Increase computer system efficiency n Sequence and schedule programs n Handle hardware errors and pProvide security for user programs

Windows 95/98 - Outline n Win95 was released in August 1995 n Total rewrite and replacement for Windows 3.x n Windows-95 “backwards compatible” with software from earlier O/S n Major, modern features include

Summary n Compatibility u It means that the ideal operating system is designed to provide execution environments for applications for other operating systems. n Portability u It means that the operating system can be ported to a variety of different machines n Robustness u It means that the ideal operating system can provide protection from accidental or deliberate damage by user programme n Usability u Easy to use, click and drag are more friendly than DOS prompt commands

Summary n Efficiency u The system functions quickly, makes optimum use of the resources n Flexibility u Adaptability to a specific environment, like Unix can be in Minicomputer or PC n Transparency u Users are unaware of all details they need not know n Security u Protecting data from unauthorized access n Integrity u Protecting itself and users from damage or any other ill effect of other’s error or malice.