CIS250 OPERATING SYSTEMS

Chapter One Introduction

Objectives Define the term Operating System Discuss the various types of Operating systems – simple batch – multiprogrammed batched – time-sharing – pc systems – parallel systems – distributed – real-time

What is an Operating System? The one program that is running at all times - the kernel A program that acts as a intermediary between a user and the hardware –It provides services to programs and users –It should ensure that the programs do not interfere with the system Provides an environment to run programs efficiently. Must be convenient to the user A control program

Four Components of a Computer System Hardware Operating system Application programs Users

Hardware CPU Memory Input/Output Devices

Operating System Resource allocator Coordinates the use of hardware among applications and the users; handles conflicts, requests. Controls resources

Application Programs Compilers Databases Games

Operating Systems History In the beginning.... –large machines were run from a console –one instruction processed at a time –program was loaded into memory manually –front panel switches were used –programmer was the operator

Early Batch Systems Software and hardware added to improve efficiency –Hardware card readers line printers magnetic tapes –Software assemblers, loaders, linkers common function libraries device drivers for each I/O device - tells OS how buffers, flags, registers, control and status bits for each device should be run

Compilers were created FORTRAN and COBOL –Programming was easier –Operating was more complex If a mistake was made, had to start over from the beginning During set up, CPU sat idle

More Complex Operating Mount FORTRAN compiler from tape –Load program through the card reader –Write to tape FORTRAN compiler produces assembly code Mount another tape for assembly Link O/P to library routines Execute binary object code Load into memory and debug

Then…Simple Batch Systems Had operators and programmers - this reduced setup time; but CPU still idle when there were errors Created automatic job sequencing - resident monitor introduced Replaced slower I/O devices (card readers, line printers) with magnetic tape

Automatic Job Sequencing Resident monitor introduced –Program in memory, transfers control from one job to the next –Job Control Language- batch programs; lack of interaction between user and job –I/O devices still slower than the CPU Replaced slower I/O devices (card readers, line printers) with magnetic tape –tape was sequential - fill tape, re-wind, unload, mount

More Processing Improvements Replaced sequential tapes with random access disk systems Developed spooling (large buffer) Job created pools to increase CPU utilization Job scheduling to administer job pool CPU scheduling

Spooling Simultaneous Peripheral Operation On-Line Uses disk as a large buffer Reads ahead for I/P devices and storing O/P files until output devices can handle them Can read I/P of one job and O/P of another

Multiprogrammed Batched Systems Job Scheduling –O/S selects the job, Loads it into memory, Executes the job –CPU utilization is increased - CPU not idle when there is work –CPU “switches” jobs; uses CPU scheduling

Terms Multi-programming: multiple programs running concurrently Multi-tasking: multiple threads within a process Multi-processing: multiple CPUs - to maximize CPU efficiency –share bus, clock and sometimes memory

Parallel Systems Symmetric - all CPUs are equal; I/O can be processed on any CPU Asymmetric - master CPU distributes tasks to slaves and the master usually does all I/O

Distributed Systems – loosely coupled, resource sharing –processes are “distributed” across systems which do not share a bus or a clock –if one system fails, the entire system does not crash Real-time Systems - control device in a dedicated application; rigid time reqmnts.