CS 1308 Computer Literacy and the Internet

Introduction

Von Neumann computer

“Naked machine”

Hardware without any helpful user-oriented features

Extremely difficult for a human to work with

An interface between the user and the hardware is needed to make a Von Neumann computer usable

2

System Software: The Virtual Machine System software

Acts as an intermediary between users and hardware

Creates a virtual environment for the user that hides the actual computer architecture

Set of services and resources created by the system software and seen by the user

3

Figure 6.1The Role of System Software

4

BIOS

Basic Input/Output System The first piece of software that starts

when the computer is turned on Stored in Flash Memory

Power-on Self-test (POST) makes sure that all the system components are running properly (e.g. RAM check)

Gets the keyboard, mouse, and other peripherals started

Finds the “Boot” device and starts the operating system

For more information (Google “How does the BIOS work”)

5

Types of System Software

System software is a collection of many different programs

Operating system Controls the overall operation of the

computer Communicates with the user Determines what the user wants Activates system programs, applications

packages, or user programs to carry out user requests

6

Functions of an Operating System

Five most important responsibilities of the operating system

User interface management

Program scheduling and activation

Control of access to system and files

Efficient resource allocation

Deadlock detection and error detection7

The User Interface

Operating systemWaits for a user command

If command is legal, activates and schedules the appropriate software package

Types of User interfacesText-oriented – DOS, Unix, Linux

Graphical – Mac, Windows, Linux

Hybrid – Cell phones, digital cameras, PDAs

Embedded –Microwave ovens, cars, etc.8

System Security And Protection The operating system must prevent

Unauthorized people from using the computer

User names and passwords

Legitimate users from accessing data or programs they are not authorized to access

Authorization lists

9

An OS provides security, e.g. against viruses!

10

16M

Shareware Game

0

Microsoft Word

Doom

DOS OS

Memory

the virus code

Shareware Game

Microsoft Word

Doom

DOS OS

Memory

When an “infected program”is run, the program counter

(PC)might take the value of the

first address of the virus code.Should this happen, the

virus code will be executed.

The virus code overwritesother programs in memory.

How might the OS prevent this?

Efficient Allocation Of Resources

The operating system ensures that

Multiple tasks of the computer may be underway at one time

Processor is constantly busy

Keeps a “queue” of programs that are ready to run

Whenever processor is idle, picks a job from the queue and assigns it to the processor

Memory and secondary storage devices are used efficiently.

11

An OS Allocates Resources Efficiently:

It’s easy for an OS that supports a single user running a single program

12

1. User tells OS to execute program2. OS finds the program on disk3. OS copies the program into memory4. OS initializes the PC to the beginning of the program5. Program monopolizes all computer resources

bus

diskmemory CPU

ALU

PCregisters

Peripherals:•monitors•printers•network connections•etc.

DoomWordWindowsNetscapeJAVASPSS

This wastes computer resources

Input and Output are very slow Disk and peripherals are 10,000x

slower than the CPU The user (typing on the keyboard) is

even slower! CPU time is wasted while waiting for

them During this time, CPU could be

executing other programs!

13

Multitasking

Although it seems like your computer is running many programs at once, including the OS, it is not.

Your computer runs a bit of one program before switching to another.

And then switching again, often because it is waiting for I/O.

Because your computer is very fast, it seems like they are all running at the same time.

14

The Future

Operating systems will continue to evolve

Possible characteristics of fifth-generation systems

Multimedia user interfaces

Parallel processing systems

Completely distributed computing environments – possibly over the internet (cloud computing)

15

Summary

System software acts as an intermediary between the users and the hardware

Your computer would be useless without an operating system and system software.

16