Operating System Course Overview, Slides of Operating Systems

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Operating System

Course Overview

 (^) Pre-Requisites

 (^) EE-321 Computer Organization and Architecture

 (^) Textbook

 (^) “ Operating System Concepts ”, By Abraham

Silberschatz, Peter Galvin, and Greg Gagne, 10th

Edition, Publisher: John Wiley and Sons

 (^) Reference Books

 (^) “ Operating Systems: Principles and Practice ” by

Thomas Anderson, Michael Dahlin, 2nd Edition

 (^) “Operating Systems. Internals and Design Principles”

by William Stallings, Prentice-Hall

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Course Objectives

 (^) To provide knowledge how operating systems work

 (^) To introduce basic resource management techniques,

issues of performance, avoiding deadlocks etc. to equip

students with sufficient knowledge about the working

mechanism of Operating System

 (^) To apply knowledge for conducting research and

development

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What is an Operating System?

 (^) A program that acts as an intermediary between a user

of a computer and the computer hardware

 (^) Operating system goals:

 (^) Execute user programs and make solving user problems

easier

 (^) Make the computer system convenient to use

 (^) Use the computer hardware in an efficient manner

Computer System Structure

 (^) Computer system can be divided into four components:

 (^) Hardware – provides basic computing resources

 (^) CPU, memory, I/O devices

 (^) Operating system

 (^) Controls and coordinates use of hardware among various

applications and users

 (^) Application programs

 (^) define the ways in which the system resources are used to

solve the computing problems of the users

 (^) Word processors, compilers, web browsers, database systems,

video games

 (^) Users

 (^) People, machines, other computers

What Operating Systems Do

 (^) Depends on the point of view

 (^) Users want convenience , ease of use and good

performance

 (^) Don’t care about resource utilization

 (^) Operating system is a resource allocator and

control program making efficient use of

Hardware and managing execution of User

programs

Operating System Definition

 (^) No universally accepted definition

 (^) “ Everything a vendor ships when you order an operating

system ” is a good approximation

 (^) But varies wildly

 (^) “ The one program running at all times on the computer ” is the

kernel, part of the operating system

 (^) Everything else is either

 (^) A system program (ships with the operating system, but not part of

the kernel) , or

 (^) An application program , all programs not associated with the

operating system

 (^) Today’s OSes for general purpose and mobile computing also include

middleware – a set of software frameworks that provide addition

services to application developers such as databases, multimedia,

graphics

Overview of Computer System

Structure

Computer System Organization

 (^) Computer-system operation

 (^) One or more CPUs, device controllers connect through common bus

providing access to shared memory

 (^) Concurrent execution of CPUs and devices competing for memory

cycles

How a Modern Computer Works

A von Neumann architecture

Multiprogramming (Batch system)

 (^) Single user cannot always keep CPU and I/O devices

busy

 (^) Multiprogramming organizes jobs (code and data) so

CPU always has one to execute

 (^) A subset of total jobs in system is kept in memory

One job selected and run via job scheduling

 (^) When job has to wait (for I/O for example), OS switches

to another job

Multitasking (Timesharing)

 (^) A logical extension of Batch systems

 (^) the CPU switches jobs so frequently that users can interact

with each job while it is running, creating interactive

computing

 (^) Response time should be < 1 second

 (^) Each user has at least one program executing in

memory  process

 (^) If several jobs ready to run at the same time  CPU

scheduling

 (^) If processes don’t fit in memory, swapping moves

them in and out to run

 (^) Virtual memory allows execution of processes not

completely in memory

Dual-mode Operation

 (^) Dual-mode operation allows OS to protect itself and other

system components

 (^) User mode and kernel mode

 (^) Mode bit provided by hardware

 (^) Provides ability to distinguish when system is running user code or

kernel code.

 (^) When a user is running  mode bit is “ user ”

 (^) When kernel code is executing  mode bit is “ kernel ”

 (^) How do we guarantee that user does not explicitly set the mode

bit to “kernel”?

 (^) System call changes mode to kernel, return from call resets it to user

 (^) Some instructions designated as privileged , only executable in

kernel mode

Transition from User to Kernel Mode 20