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

2. Fall 2000M.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

3. Fall 2000M.B. Ibáñez Abstract View of System Components

4. Fall 2000M.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

5. Fall 2000M.B. Ibáñez Evolution of Operating Systems Serial 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

6. Fall 2000M.B. Ibáñez Evolution of Operating Systems Simple 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 $LOAD $RUN $END

7. Fall 2000M.B. Ibáñez Memory Layout For a Resident Monitor Boundary Interrupt Processing Device Drivers Job Sequencing Control Language Interpreter User Program Area Monitor

8. Fall 2000M.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

9. Fall 2000M.B. Ibáñez Multiprogrammed Batch Systems

10. Fall 2000M.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/hr12 jobs/hr Mean response time 18 min.10 min.

11. Fall 2000M.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

12. Fall 2000M.B. Ibáñez Primitive Time-sharing Operating System

13. Fall 2000M.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

14. Fall 2000M.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

15. Fall 2000M.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

16. Fall 2000M.B. Ibáñez Characteristics of Modern Operating Systems Multithreading 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

17. Fall 2000M.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

18. Fall 2000M.B. Ibáñez Characteristics of Modern Operating Systems Distributed operating systems provides the illusion of a single main memory used for distributed file system

19. Fall 2000M.B. Ibáñez Outline of the Course Processes Memory I/O devices File systems Protection and security