Unit 1-Introduction-to-OS-Tan

8/7/2019 Unit 1-Introduction-to-OS-Tan

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Computer People 2000 1

Unit 1

Introduction to Operating System


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What is an Operating System?

An OS is a program which act as an interfacebetween a user of computerand computerhardware.

Keyboard Mouse

PrinterRAM/ROM

HDMemBus

SystemBus

Monitor

CD

Processor

FloatingPointUnit

IntegerUnit

Cache

ControlUnit


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Layered View of a Computer System


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What is an Operating System?

An OS is a control program, which controls andcoordinate the use of Hardware among thevarious application program for the varioususers.

The OS is similar to Government. The OS is a resource allocater.

(CPU time, memory space, file storage space,input/output devices).

Primary Goal : convenience of the user. Secondary Goal: efficient operation of computer

system.


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History of Operating System-The First Generation(1945-1955)

The computers were built with tens of thousandsofvacuum tubes, were very slow.

A single group of people designed, programmed,

operated and maintained each machine. All programming was done in machine language

by wiring up plugboards to the control machinebasic functions.

Programming language were unknown.

Only numerical calculation were carried out.


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History of Operating System-The Second Generation(1955-1965)

The introduction oftransistors made possible tobuild reliable system that can be sold to thecustomers.

This also made separation between program,operator and other personals.

These systems were used for scientific andengineering calculations.


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History of Operating SystemThe Second Generation(1955-1965)

For example: If a programmer wants to run aFortran, he will follows following steps.

Load Fortran Complier.

Program read from card reader to magnetictape.

Compiler produced assembly language code

to tape. Assembly to binary code to tape and then to

the user result.


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Setup time was main problem in perviousoperation.

To solve this problem two fold solution were

developed. Professional computer operators hired to reducedsetup time.

Jobs with similar needs were batched togetherandrun through the computer as group.

There were still problems with this approach.

When a job stopped, the operator has to takenotice which program has problem.


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History of Operating System-Simple Monitor

Loader

Job sequencing

Control CardInterpreter

User programarea

Monito

r


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CPU

Card reader Line Printer

CPU

Card reader Tape Drivers Tape Drivers Line Printer


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History of Operating System-The Third Generation(1965-1980)

ICs and Multiprogramming (Mini Computers)

Previously 7094 were used for scientificapplication.

1401 were used for commercial use. IBM introduced system 360 to cater both needs

in one system.

For this a complicated OS were introduced to

handle all these computations. Multiprogramming were also introduced in this

generation.


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History of Operating System-Multiprogramming

In multiprogramming the computer is asked to runseveral programs at the same time.

The processor could be kept busy for the most of timeby switching from one program to another in the rapid

succession. In a batch multiprogramming system, a series of jobs

are loaded into memory at the same time, while onejob is waiting for an I/O transfer another job is started.

JOB A Running I/O Wait Running I/O Wait JOB B I/O Wait Running I/O Wait Running


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History of Operating System-Time Sharing

A time sharing OS use CPU scheduling andmultiprogramming to provide each user wit asmall portion of a time shared computer.

This system allows many users tosimultaneously share the computer.

CPU switches rapidly from one user to next.

Early computer was not interactive system. One programmer at a time.

Batch system no interaction.


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History of Operating System-The Forth Generation(1980-1990)

LSI made it possible to built PC for personal use. Two famous OS were introduced. MS-DOS and Unix

Also introduced Network and distributedoperating systems. Networking OS, the users are aware of the

existence of multiple computer, and can log in toremote machines and copy files from one

machine to another. Each machine runs its own local OS and has its

own user.


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History of Operating System-Distributed System

Recent trend in computer system is to distributecomputation among several physical processes.

Two such systems are available.

Tightly Coupled System: the processorsshares memory and clock.

Loosely Coupled System: the processors donot share memory and clock, such processors

has its own local memory.


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Operating System Concepts

OS has four major concepts.

Process

Files

System Call

The Shell


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Process:

Process is the program in execution.

It consisted of the executable program, theprograms data, and Stack, program counter,stack pointer and other registers.

All these information are stored in the process

table.


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Files: Files consists of sequence of bit, byte, lines or

records whose meanings are defined by its

creator.

Files are mapped by the OS on to the physicaldevices.

The OS provides a uniform logical view ofinformation storage.


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Following major tasks are performed by OS.

The creation and deletion of files.

The creation and deletion of files.

The support of primitives for manipulating filesand dir.

Mapping files onto secondary storage.

The backup of files on stable storage media.


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System Calls: User programs communicate with the OS and

request services from it by making System Calls.

Corresponding to each System Call is a LibraryProcedure.

This procedure puts the parameter of the SystemCall in a register and then issues a TRAPInstruction.

The TRAP Instruction is executed to changemode from user to kernel.

Control goes to Operating System.


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OS determines which system call is to be carriedand examines the parameters.

Kernel indexes the dispatch table, which

contains pointers to service routines for systemcalls.

If the parameters are valid, OS performs tasks.Otherwise it return error.

For example: Count = read (file, buffer, nbytes);


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The Shell:

Editors, compilers, assemblers, linkers andcommand interpreters are not the part of OS.

UNIX command interpreter is called The Shell.

Shell make heavy use of many OS features.

It is interface between a user and the OS.

When any user log in, a shell is started up. The Shell has terminal as standard input and

standard output.


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Operating System Structure

Monolithic Systems:

The structure is that there is on structure.

The OS is written as a collection ofprocedures.

Each procedure can call otherprocedurewhenever it needs.

In this approach all the individual procedures are

complied together into single object file with thelinker.


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Operating System Structure

Basic structure for the OS:

A main program invokes the requestedservice procedure.

A set ofservice procedures that carry out thesystem call.

A set ofutility procedure that helps the service

procedures.


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Operating System StructureLayered System

The OS is broken up into a number of layers.

Bottom layer is hardware and the topmost layeris the user interface.

A typical layer consists of data structures and aset of routines to service the layer above it.

The major difficulty with layered approach is

careful definition of layers, because a layer canonly use the layers below it.

Less efficient than other approaches.


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Operating System StructureVirtual Machines

The timesharing OS provides: 1. Multiprogramming 2. An extended machine with a convenient interface

than the bare hardware.

The heart of the system runs on bare hardwareand does multiprogramming with several virtualmachines to the next layer up.

Each Virtual machine is identical to the true

hardware. Each can run any OS that run directly to thehardware.


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Operating System StructureVirtual Machines

For time sharing, this machine can runinteractive system call called CMS(Conversational Monitoring system).

CMS CMS CMS

Vm/370

370 Bare Hardware

System Calls

TrapI/OInstructions

Trap


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Operating System StructureClient Server Model

In this module Kernel handle the communicationbetween clients and servers.

By splitting the OS up into parts, each of which

handles one facet of the system. Such as fileservice, process service or memory services.

Advantage of this OS is its adaptability to use indistributed system.


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Operating System StructureClient Server Model

Client

Process

Client

Process

Process

Server

Terminal

Server File

Server

Memory

Server

Kernel

User Mode

Kernel ModeClient Obtain serviceBy sending messageTo server processes


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Windows NT Client-ServerStructure

Unit 1-Introduction-to-OS-Tan

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