THE OPERATION SYSTEM The need for an operating system Layered view of a computer Functions of the operating system Types of operating system Microcomputer operating systems

Need for an OS Computer hardware and machine code only is vary hard to use Users have to communicate with the computer Many users want to use resources of the computer simultaneously Programs may interfere with others’ programs or the overall system Many users may know little about computers

Layered View of a Computer hardware machine code operating system systems programming language compiler / interpreter applications programming language applications package

Types of OS batch processing (jobs in a queue) multiprogramming (or multitasking) time sharing real-time processing

Need for an OS Operating System is a collection of system programs that supervise, control and coordinate the resources and overall operation of the computer system Provides an interface between the user, the computer and the applications.

Functions of an OS Supervise programs while they are running scheduling of jobs, overcome problems Communicate with users (e.g. display messages) Provide utilities to manage the computer system File manager, utility tools Optimize the use of resources of the computer system hw/sw resources(CPU, memory, I/O devices), priorities

Functions of an OS Keep a log of actions taken on all programs Records important events(e.g. illegal operation, errors) Maintain security User accounts and passwords, file security among users and groups Handle errors

OS Communicate with users Supervise programs Provide untilities Keep log of events Optimize use of resources Handle errors Maintain security

Batch processing jobs are put in a batch queue until it is their turn to be run one job cannot start until the previous one is complete most suitable for ‘long’ programs or processes involves large volume of data waste of CPU time as it is waiting for the operation of peripheral devices  spooling

Multiprogramming (multitasking) a no. of different jobs are handled at the same time by the CPU the OS makes use of the time during which a task is waiting for input/output operations to work on another program the capacity of a given computer increases support both batch & interactive jobs

Time sharing (multi-access) due to the fact that the CPU is not in use for most of the time hundreds of terminals are connected by telephone lines to the central computer OS allocate time slice to each user to interact with the CPU (in the central computer) whenever needed supports multiprogramming

Real-time processing computer responds in real time data are processed immediately after input the computer system is dedicated to 1 application only for applications which a very fast response is needed (no delay for even 1 sec.) e.g., anti-missile defence system, aeroplane landing control system

Microcomputer Operating Systems OS programs are commonly stored on a floppy disk or a hard disk Disk Operating System (DOS) before using a microcomputer, one must load the OS or ‘boot’ the system OS then is transferred from disk to main memory, the system is activated - ‘alive’ Kernel – the core part that always reside in mem.

Examples of OS DOS 3.3 (Apple II, 1980’s) PC DOS, MS DOS (IBM XT/AT) Window 3.1 Window 95, 98, Me, NT, 2000 Mac OS Linux Unix (minicomputer to mainframe)