TOPIC1-INTRO os

8/7/2019 TOPIC1-INTRO os

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BITS 1213 - Operating Systems 1

Introduction:

Operating System Overview

Topic 1


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Consists of the

most used andmost fundamental

components of the

OS


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Operating Systems (OS) O/S controls the execution of application

programs and acts as an interface between

applications and the computer hardware O/S objectives:

to make a computer more convenience to use

to efficiently use the computer system resources

to permit the effective development, testing and

introduction of new system functions without

interfering with service


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The O/S provides services in the following

areas:

1. Facilities for Program creation editors,compilers, linkers, and debuggers

2. Program execution loading in memory, I/Oand file initialization

3. Access to I/O and files deals with the specificsof I/O and file formats

4. System access Protection in access toresources and data Resolves conflicts for resource

contention

OS Services


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OS Services

5. Error detection and response

eg. Memory failure, ending a program and report error .6. Accounting

eg. used for billing users (on multiuser systems)

eg. collect statistics on resource usage


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Evolution of OS Must adapt to hardware upgrades and newtypes of hardware.

Examples: Character vs graphic terminalsIntroduction of paging hardware

Must offer new services, eg: internetsupport

The need to change the OS on regular basisplace requirements on its design modularconstruction with clean interfaces object oriented

methodology


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The Evolution of O/S

Serial Processing

Simple Batch Systems

Multiprogrammed

Batch Systems

Time-Sharing Systems


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Serial Processing No operating system

The programmer interacted directly with the

computer hardware Machine run from a console, consisting of display

lights, toggle switches, input device and a printer

These systems presented two main problems:

scheduling result in wasted computer idle time orinsufficient allotted time

requires a considerable amount of setup time


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The concept of batch operating system was introduced

to improve utilization

The idea was to use a software known as the monitor

the user no longer has direct access to the machine

The user submit a job (written on card or tape) to a

computer operator.

The computer operator place a batch of several jobs on ainput device.

Monitor manages the execution of each program in the

batch.


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Monitor reads jobs one at a timefrom the input device.

Monitor places a job in the user

program area. Each program is constructed to

branch back to the monitor when itcompletes processing

the monitor would automaticallybegin loading the next program


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Machine time alternates between execution of user

programs and execution of the monitor

Two sacrifices:

some main memory is now given over to the

monitor

some machine time is consumed by the monitor both of these are forms of overhead



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Uniprogramming The processor is often idle.

I/O devices is slow compared to the processor

the processor spends a certain amount of time executinguntil it reaches an I/O instruction

it must wait until that I/O instruction concludes before

proceeding


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Expand memory to hold two, three or more

programs

when one job needs to wait for I/O, the processor canswitch to the other job no waiting for I/O

known as multiprogramming or multitasking

Multiprogramming uses hardware that supports

I/O interrupts and DMA (direct access memory)

Memory management is needed requires

scheduling algorithm

Multiprogrammed Batch Systems


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Multiprogramming


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Multiprogramming


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Time-Sharing Systems To provide a mode for interactive jobs

Multiprogramming can be used to handle multiple

interactive jobs the technique is known as time sharing

the processors time is shared among multiple users

Multiple users simultaneously access the system

through terminals the operating system interleaving the execution of each

user program in a short burst or quantum ofcomputation


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Assume that there are four interactive users with

the following memory requirement:

JOB1: 15,000

JOB2: 20,000

JOB3: 5,000

JOB4: 10,000


(Example)


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(Example)


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Major Achievements Five major theoretical advances in the

development of operating systems:

processes

memory management

information protection and security

scheduling and resource management

system structure


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(1) Processes A program in execution

An instance of a program running on a computer

The entity that can be assigned to and executed on

a processor

A unit of activity characterized by a single

sequential thread of execution, a current state, andan associated set of system resources


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Process Consists of three components

An executable program

Associated data needed by the program

Execution context of the program

All information the operating system needs to manage the

process


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(2) Memory Management Process isolation

Automatic allocation and management

Support for modular programming

Protection and access control

Long-term storage


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(3) Information Protection and

Security Availability

Protecting system against interruption

ConfidentialityUsers cannot read data for which data is unauthorized

Data integrity

Protection data from unauthorized modification

Authenticity

proper verification of the identity of users and validity ofmessages or data


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(4) Scheduling and Resource

Management Fairness

give equal and fair access to all processes

Differential responsiveness discriminate between different classes of jobs

Efficiency

maximize throughput, minimize response time, and

accommodate as many uses as possible


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Major Elements of Operating

System


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(5) System Structure View the system as a series of levels

Each level performs a related subset of functions

Each level relies on the next lower level to

perform more primitive functions

This decomposes a problem into a number of more

manageable sub problems


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Operating System Design

HierarchyLevel Name Objects Example Operations

13 Shell User programming Statements in shell language

environment

12 User processes User processes Quit, kill, suspend, resume

11 Directories Directories Create, destroy, attach, detach,

search, list

10 Devices External devices, such Open, close,

as printer, displays read, write

and keyboards

9 File system Files Create, destroy, open, close

read, write

8 Communications Pipes Create, destroy, open. close,

read, write


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7 Virtual Memory Segments, pages Read, write, fetch

6 Local secondary Blocks of data, device Read, write, allocate, free

store channels

5 Primitive processes Primitive process, Suspend, resume, wait, signal

semaphores, ready

list


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4 Interrupts Interrupt-handling Invoke, mask, unmask,

programs retry

3 Procedures Procedures, call stack, Mark stack, call, return

display

2 Instruction Set Evaluation stack, micro- Load, store, add, subtract

program interpreter, branch

scalar and array data

1 Electronic circuits Registers, gates, buses, Clear, transfer, activate,

etc. complement

Level 1-4 represents hardware


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Characteristics of Modern

Operating Systems Microkernel architecture

Small operating system core

Contains only essential operating systems functions

Many services traditionally included in the operating system are nowexternal subsystems

device drivers

file systems

virtual memory manager

windowing system security services

Multithreading

process is divided into threads that can run simultaneously


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Thread

dispatchable unit of work

executes sequentially and is interruptable Process is a collection of one or more threads

Symmetric multiprocessing

there are multiple processors

these processors share same main memory andI/O facilities

All processors can perform the same functions


Operating Systems


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Operating Systems Distributed operating systems

provides the illusion of a single main memory and

single secondary memory space used for distributed file system

Object-oriented design

used for adding modular extensions to a small kernel

enables programmers to customize an operating systemwithout disrupting system integrity

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