Fall 2000M.B. Ibáñez Lecture 01 Introduction What is an Operating System? The Evolution of Operating Systems Course Outline.

Fall 2000 M.B. Ibáñez

Lecture 01Introduction

What is an Operating System?

The Evolution of Operating Systems

Course Outline

Fall 2000 M.B. Ibáñez

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 – Make solving user problems easier– Allocate resources in a efficient and fair way

Fall 2000 M.B. Ibáñez

Abstract View of System Components

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Hardware

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lots of different components,with different speds,different protocols for communication

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user 1 user 2 user n

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They want low cost and efficient services

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compiler text editor database system

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They want to have an easy life (don’t have to worry about speeds,use of file instead of blocks, large memory, etc)

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Operating System

Fall 2000 M.B. Ibáñez

Services given by an Operating System

• Efficient program execution– Keeping all the devices busy– Good throughput for the user

• Access to I/O devices

• Controlled access to system and files

• Error detection and response

• Accounting

Fall 2000 M.B. Ibáñez

Evolution of Operating SystemsSerial Processing

• From the late 1940s to the mid-1950s• There was no Operating System

– These machines were run from a console, consisting of display lights, toggle switches, some form of input device, and a printer

• Job scheduling– A user used a sign-up sheet to reserve machine time.

• How to run a job?– Load the compiler and source program into memory– Save the object program– Loading and linking together the object program and common functions

Fall 2000 M.B. Ibáñez

Evolution of Operating SystemsSimple Batch Systems

• Mid-1950s

• The users did not interact directly with the computer system. The operator would sort programs into batches with similar requirements.

• The user prepared a job. A Monitor executed the job.$JOB

$FTN

<FORTRAN instructions>

$LOAD

$RUN

<data>

$END

Fall 2000 M.B. Ibáñez

Memory Layout For a Resident Monitor

Boundary

InterruptProcessing

DeviceDrivers

JobSequencing

Control LanguageInterpreter

UserProgram

Area

Monitor

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From Operating Systems.Internals and Design Principles.W. Stalling. Prentice Hall

Fall 2000 M.B. Ibáñez

There are some hardware features desirable

• Memory protection the user program should not alter the monitor’s

area

• Timer to prevent a single job from monopolizing the

system

• Privileged instructions I/O instructions by example

Fall 2000 M.B. Ibáñez

Multiprogrammed Batch Systems

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time

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A

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A

a

A

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B

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B

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time

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A

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B

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A

a

B

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A

Fall 2000 M.B. Ibáñez

Effects of Multiprogramming

Uniprogramming Multiprogramming

Processor use 17% 33%

Memory use 30% 67%

Disk use 33% 67%

Printer use 33% 67%

Elapsed time 30 min. 15 min.

Throughput rate 6 jobs/hr 12 jobs/hr

Mean response time 18 min. 10 min.

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From Operating Systems.Internals and Design Principles.W. Stalling. Prentice Hall

Fall 2000 M.B. Ibáñez

Time-sharing systems

• 1960s, they become common early 1970s

• Multiprogramming allows the processor to handle multiple batch jobs at a time

– Main objective: Maximize processor use

• Multiprogramming can be used to handle multiple interactive jobs: time -sharing

– Main objective: Minimize response time

• Processor time is shared among multiple users

• Multiple users simultaneously access the system through terminals

Fall 2000 M.B. Ibáñez

Primitive Time-sharing Operating System

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Monitorjob 1free

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Monitorfreejob 2

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Monitorfreejob2job3

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Monitorfreejob1job3

Fall 2000 M.B. Ibáñez

New problems for the Operating Systems

• Multiple jobs are in memory– They must be protected from interfering with each other

• Multiple interactive users– The file system must be protected so that only authorized

users have access to a particular file

• The contention for resources, such as printers and mass storage devices, must be handled

Fall 2000 M.B. Ibáñez

Characteristics of Modern Operating Systems.What forces a change?

Developments in hardware

• Multiprocessor machines

• Greatly increased machine speed

• High-speed network attachments

• Increasing size and variety of memory storage services

New applications

• Multimedia applications

• Internet and Web access

• client/server computing

Fall 2000 M.B. Ibáñez

Characteristics of Modern Operating Systems Microkernel architecture

• A microkerner architecture assigns only a few essential functions to the kernel, such as– Address spaces

– Interprocess communication

– Basic scheduling

• The microkernel approach simplifies implementation, provides flexibility, and is well suited to a distributed environment

Fall 2000 M.B. Ibáñez

Characteristics of Modern Operating SystemsMultithreading

• Multithreading– technique in which a process, executing an application,

is divided into threads that can run simultaneously

• Thread– dispatchable unit of work

– executes sequentially and is interruptable

• Process – collection of one or more threads

Fall 2000 M.B. Ibáñez

Characteristics of Modern Operating Systems Symmetric multiprocessing (SMP)

• Systems with multiple multiprocessors– there are multiple processors

– these processors share same main memory and I/O facilities

– All processors can perform the same functions

• Advantages over uniprocessor architectures– Performance

– Availability

– Incremental growth

– Scaling

Fall 2000 M.B. Ibáñez

Characteristics of Modern Operating Systems Distributed operating systems

• provides the illusion of a single main memory

• used for distributed file system

Fall 2000 M.B. Ibáñez

Outline of the Course

• Processes

• Memory

• I/O devices

• File systems

• Protection and security