10/06/ :03:20 CSC Alliance — 1 Kimera Richard Phone: INSTITUTE OF COMPUTER SCIENCE DEPARTMENT OF INFORMATION TECHNOLOGY Kimera Richard Phone: INSTITUTE OF COMPUTER SCIENCE DEPARTMENT OF INFORMATION TECHNOLOGY Introduction to operating systems: BIT 2104 Chapter 1: Introduction and Overview Thursday 5 th September

MUST- ICS Chapter 1: Introduction  An operating system is a program that manages the computer hardware.  It also provides a basis for application programs and acts as an intermediary between a user of a computer and the computer hardware.  An amazing aspect of OSs is how varied they are in accomplishing these tasks.  Mainframe OSs are designed primarily to optimize utilization of hardware.

MUST- ICS Chapter 1: Introduction  Personal computer (PC) OSs support complex games, business applications, and more customizations  Handheld computer OSs are designed to provide an environment in which a user can easily interface with the computer to execute programs.  Thus, some OSs are designed to be convenient, others to be efficient, and others some combination of the two.

MUST- ICS Chapter 1: Introduction  To understand what OSs are, we must first understand how they have developed.  In this chapter, we trace the development of OSs from the first hands-on systems through multiprogrammed and time-shared systems to PCs, and handheld computers.  We also discuss OS variations, such as parallel, real-time, and embedded systems.  As we move through the various stages, we see how the components of OSs evolved as natural solutions to problems in early computer systems.

MUST- ICS Chapter 1: Introduction  What is an Operating System?  Mainframe Systems  Desktop Systems  Multiprocessor Systems  Distributed Systems  Clustered System  Real -Time Systems  Handheld Systems  Computing Environments

MUST- ICS 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.

MUST- ICS Computer System Components  Hardware – provides basic computing resources (CPU, memory, I/O devices).  Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.  Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).  Users (people, machines, other computers).

MUST- ICS Figure 1.1 Abstract view of Components of a computer system.

MUST- ICS Operating System Views  Resource allocator – manages and allocates resources.  Control program – controls the execution of user programs and operations of I/O devices.  Kernel – the one program running at all times (all else being application programs). services include, but are not limited to: disk access, memory management, task scheduling, and access to other hardware devices.

MUST- ICS Early Systems (1950s))  Structure: Large machines run from console, Single user system, Programmer/User as operator, Paper tape or punched cards  Early software : Assemblers, compilers, linkers, loaders, device drivers, libraries of common subroutines.  Low CPU utilization, high setup time.

MUST- ICS Batch Processing (Mainframe Systems)-1960  Batch processing is mainly associated with mainframe computers. Reduce setup time by batching similar jobs  Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system.  Add a card reader, Hire an operator  Common Batch processing usage are; Data processing, printing, databases, image editing, converting of files from one format to another.

MUST- ICS Batch Processing  Resident Monitor: Program that always resided in memory and was used to hold initial control, control transfers to job and then back to monitor.  This was achieved by putting all the instructions the monitor was to use on a patch card

MUST- ICS Memory Layout for a Simple Batch System

MUST- ICS Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. As other programs perform input/out, control is taken to another program

MUST- ICS OS Features Needed for Multiprogramming  I/O routine supplied by the system.  Memory management – the system must allocate the memory to several jobs.  CPU scheduling – the system must choose among several jobs ready to run.  Allocation of devices.

MUST- ICS Time-Sharing Systems–Interactive Computing  The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).  A job swapped in and out of memory to the disk.  On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.  On-line system must be available for users to access data and code.

MUST- ICS Time – sharing continued  Allow interactive terminal access to computer, with many users sharing.  Early system (CTSS, Cambridge, Mass.) gave each user 0.2s of CPU time;  monitor then saved user program state, loaded state of next scheduled user.  Control card interpreter replaced by command language interpreter.

MUST- ICS Time sharing systems (Western Electric Teletype)

MUST- ICS Desktop Systems  Personal computers – computer system dedicated to a single user.  I/O devices – keyboards, mice, display screens, small printers.  User convenience and responsiveness.  Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features.  May run several different types of operating systems (Windows, MacOS, UNIX, Linux)

MUST- ICS Desktop Operating Systems (Apple Macintosh which was introduced in 1984) Reference:

MUST- ICS Parallel Systems  Multiprocessor systems with more than one CPU in close communication.  Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory.  Advantages of parallel system:  Increased throughput  Economical  Increased reliability

MUST- ICS Parallel Systems (Cont.)  Symmetric multiprocessing (SMP)  Each processor runs and identical copy of the operating system.  Many processes can run at once without performance deterioration.  Most modern operating systems support SMP  Asymmetric multiprocessing  Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.  More common in extremely large systems

MUST- ICS Symmetric Multiprocessing Architecture

MUST- ICS Distributed Systems  Distribute the computation among several physical processors.  Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines.  Advantages of distributed systems.  Resources Sharing  Computation speed up – load sharing  Reliability  Communications

MUST- ICS Distributed Systems (cont)  Requires networking infrastructure.  Local area networks (LAN) or Wide area networks (WAN)  May be either client-server or peer-to-peer systems.

MUST- ICS General Structure of Client-Server

MUST- ICS Clustered Systems  Clustering allows two or more systems to share storage.  Provides high reliability.  Asymmetric clustering: one server runs the application while other servers standby.  Symmetric clustering: all N hosts are running the application.

MUST- ICS Real-Time Systems  Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.  Well-defined fixed-time constraints.

MUST- ICS Real time systems forms  Hard real-time - systems where it is absolutely imperative that responses occur within the required deadline. E.g. Flight control systems.  Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM)  Conflicts with time-sharing systems, not supported by general- purpose operating systems.  Soft real-time - systems where deadlines are important but which will still function correctly if deadlines are occasionally missed. E.g. Data acquisition system.  Limited utility in industrial control of robotics  Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

MUST- ICS Real-Time Systems (Cont.)  Real real-time - systems which are hard real-time and which the response times are very short. E.g. Missile guidance system.  Firm real-time - systems which are soft real-time but in which there is no benefit from late delivery of service.

MUST- ICS Handheld Systems  Personal Digital Assistants (PDAs)  Cellular telephones  Issues:  Limited memory  Slow processors  Small display screens.

MUST- ICS Migration of Operating-System Concepts and Features

MUST- ICS Windows Evolution

MUST- ICS Homework 1.What are the three main purposes of an operating system? 2.An extreme method of spooling, known as staging a tape, is to read the entire contents of a magnetic tape onto disk before using it. Discuss the main advantage of such a scheme. 3.In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a) What are two such problems? b) Can we ensure the same degree of security in a time-shared machine as we have in a dedicated machine? Explain your answer. 4.What is the main advantage of multiprogramming? 5.What are the main differences between operating systems for mainframe computers and personal computers?

MUST- ICS Homework 1.Define the essential properties of the following types of operating systems: a. Batch, b. Interactive, c. Time sharing, d. Real time, e. Distributed 2.We have stressed the need for an operating system to make efficient use of the computing hardware. When is it appropriate for the operating system to forsake this principle and to “waste” resources? Why is such a system not really wasteful? 3.Under what circumstances would a user be better off using a time-sharing system, rather than a personal computer or single-user workstation? 4.Why are distributed systems desirable? 5.What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment? 6.What is the purpose of the “resident monitor”? To perform orderly and efficient automatic job sequencing, regardless of errors that might arise. 7.What were control cards used for? To let monitor know what resources are needed for current job, such as compiler, linker, data, etc., when to use them, and with which file; and to tell monitor when it reaches end of job.

MUST- ICS Reference Books  W. Stallings Operating Systems: Internals and Design Principles (4thedition), Prentice-Hall,  A. Silberschatz and P. Galvin Operating Systems Concepts (5th edition),Addison- Wesley,  Most of the other major OS texts are also suitable.

MUST- ICS  Questions? Thanks for yr attention! Lets keep the ball rolling !