Chapter 1 OS Overview CIS 106 Microcomputer Operating

Chapter 1 - OS Overview CIS 106 Microcomputer Operating Systems Gina Rue CIS Faculty Ivy Tech State College Northwest Region 01

Introduction What is an operating system? • Executive Manager - the part of the computer that manages all of the hardware and all of the software 2

Five Major OS Components • Memory Manager • Processor Manager • Device Manager • File Manager • User Command Interface See Fig. 1. 1 p. 4 3

OS Subsystem Manager Tasks • Monitor its resources continuously • Enforce the policies that determine who gets what, when and how much • Allocate the resources - reclaim it - when appropriate • Deallocate the resource - reclaim it when appropriate See Figure 1. 2 p. 5 4

OS Subsystem Managers • Memory is in charge of main memory. • Process decides to how to allocate the CPU. • Device monitors every device, channel & control unit. • File keeps track of every file in the system. See p. 6 Seven program execution steps 5

Machine Hardware • Hardware - the physical machine and its electronic components. • Software - instructions (programs) written for computer systems. • I/O devices - every physical peripheral unit in the system. See Fig. 1. 3 p. 7 6

Machine Hardware • Mainframe - IBM 360, 1964. Large physically in size and memory • Minicomputers - Digital Equipment Corporation, early ‘ 70 s-. Used by smaller institutions, schools, colleges • Microcomputer - single user system, late ‘ 70’s. Targeted for small business market 7

OS Types • Batch throughput - efficiency : measures # of jobs completed in a given amount of time • Interactive • Real-time • Hybrid 8

History of OS Development • First generation - (1940 -1955) – Assemblers/Compilers translate binary code & English-like commands – System software, macros, programs, utility program and device driver creation – Device driver subroutines written to standardize input and output 9

History of OS Development • Second generation - (1955 -1965) – More cost effective for business environment – Improvements: Computer operators & job scheduling • job scheduling - groups together programs with similar requirements – (JCL) Job Control Language • assists OS manage system resources by identifying users and their jobs, and specify resources to execute each job 10

History of OS Development • Improved CPU performance (2 nd gen. cont. ) – Speed of I/O devices – Use more available storage by blocking records before retrieval and storage • Blocking - several logical records grouped within one physical record – Reduce discrepancy in speed between I/O and CPU – Spooling, program libraries, file access methods, timer interrupts, serial batch 11

History of OS Development • Third generation - (mid-1960 s) – Designed with faster CPU – Relatively slow I/O devices – Solution multiprogramming • concept of many programs sharing the attention of a single CPU • interrupt - CPU notified of events needing OS services 12

History of OS Development • Multiprogramming systems – passive multiprogramming – active multiprogramming – virtual memory – firmware – multiprocessing 13

History of OS Development • Passive Multiprogramming – OS didn’t control interrupt – OS waited for each job to end – Ideal for nonstop processing before issuing an interrupt “CPU-bound” – It would tie up the OS for long periods of time 14

History of OS Development • Active Multiprogramming – allows each program to use a slice of time – when time expired, the job was interrupted by another job – each interrupt job had to wait its turn 15

History of OS Development • Virtual Memory – took advantage of the fact that the CPU could only process one instruction at a time – the entire program didn’t have to reside in memory before execution – divides the programs into segments keeping them in secondary storage 16 until needed

History of OS Development • Firmware – OS was made part of hardware – a program is permanently held in ROM (read only memory) – many programming functions were being carried out by the OS – made programmer’s task simpler 17

History of OS Development • Multiprocessing – more than one processor – more complex languages were designed to coordinate activities – possible to execute programs in parallel 18

History of OS Development • Evolution of personal computers & high-speed communication moved on to: – distributed processing – networked systems – enabling shared hardware & software resources from remote locations 19

Summary • OS functions • Evolution of increasingly complex computers and computer systems General Picture: • hardware and software roles 20