System Software. System software includes all of the programs needed to keep a computer and its...

System Software

System software includes all of the programs needed to keep a computer and its peripheral devices running smoothly

Two major categories of system software are:◦ Operating systems ◦ System utilities

© Prentice-Hall, Inc

The operating system (OS) is a set of programs that perform certain basic functions with a specific type of hardware

Examples of functions of the OS are:◦ Starting the computer

◦ Managing programs

◦ Managing memory

◦ Managing files

◦ Handling messages from input and output devices

◦ Enabling user interaction with the computer


OS stays behind the scenes All software depends on the OS


OperatingOperatingSystemSystem

GUI

Resource allocation◦ Assigning computer resources to certain

programs and processes for their use

Main issues related to resource allocation◦ Sharing the Central Processing Unit (CPU)◦ Sharing memory◦ Sharing storage resources◦ Sharing printing resources


Multiprocessing Multiprogramming Time-Sharing


The use of a powerful computer with multiple CPUs

Multiple programs run simultaneously◦ Each runs on its own processor


Two or more programs executed concurrently◦ Programs take turns using the CPU◦ Event-driven

An interrupt suspends processing to allow another program to run

After the second program runs, the OS returns the CPU to another program


Programs take turns using the CPU Time-driven

◦ Each user is given a slice of time (fraction of a second)

◦ CPU works only on that user’s tasks during his/her time slice

Typically used in applications with many users


Single-tasking systems run one application program at a time

Multitasking OSs have the ability to run more than one application program at a time

Multitasking is accomplished by◦ A foreground application

The active program or program in use

◦ One or more background applications

Inactive program(s) or program(s) not in use© Prentice-Hall, Inc

Background application

Foreground application


Access Windows Task Manager by pressing Ctrl + Alt + Del, select the Start Task Manager option, and then click the Processes tab

First review Von-Neumann architecture◦ System component: CPU, Memory and IO◦ Programs must be in main memory (RAM) to execute◦ cycle under Von-Neumann architecture

Load instruction from memory into instruction register

Operands fetched from memory to internal registersSTART

Fetch next instruction fromMemory to IR, Increment PC

Decode Instruction and fetch data if needed

ExecuteInstruction in IR

STOP ?NO YES

Ideally, we want programs and data to reside in main memory permanently◦ Main memory is usually too small◦ Main memory is volatile – loses contents on power

loss Secondary storage holds large quantities of data,

permanently◦ Magnetic disk is the most common secondary-

storage device

◦ Actually, a hierarchy of storage varying by speed, cost, size and volatility


The operating system allocates memory areas for each running program; it keeps programs from interfering with each other

The operating system uses virtual memory as an extension of random access memory (RAM)



least recentlyused data or

program instructions

pageswapped

out

swap file

Virtual memorymanagement

hard diskpage

swapped in

most recentlytransferred data or

program instructions

memory

Paging: The process of transferring files from the hard disk to RAM and back

You are going to do some research on a particular topic. Thus, you go to the library and look for the a shelve that contains books on that particular topic

You pick up a book from the shelve, find a chair, seat and start reading


You find a reference to another book on the same topic that you are also interested in reading. Thus, you stand up, go to the same shelve, leave the first book and pick up the other book

Then, you go back to the chair and start reading the second book

Later on you realize that you want to read the first book once again (or another related book). Thus, you repeat the same process (i.e., go to the shelve to find it) © Prentice-Hall, Inc

Suppose that instead of taking just one book from the shelve, you take 10 books on the same topic. Then, you find a table with a chair, put the 10 books on the table, sit there and start reading one of the books

If you need another related book, there is a good chance that it is on your table so you don’t have to go to the shelve to get it. Also, you can leave the first book on the table and there is a good chance that you will be needing it again later


cache are relatively smaller and faster to access compared to main memory

Data are transfer to cache with the hope that future requests for that data can be served faster


Input and output devices generate interrupts, or signals, that tell the operating system that something has happened

The OS provides interrupt handlers or mini-programs that begin when an interrupt occurs


Discovering Computers 2012: Chapter 823

Page 408

The user interface is that part of the OS with which the user interacts with a computer


Graphical user interface (GUI)◦ Uses graphics to create a desktop environment◦ Icons (small pictures) represent computer

resources◦ Programs run within on-screen windows

Menu-driven◦ Text-based menus are used to show all of the

options available to the user Command-line

◦ The user is required to type keywords or commands in order to enter data or give instructions





Operating systems typically provide a means to establish Internet connections


Page 408 Figure 8-10

A performance monitor is a program that assesses and reports information about various computer resources and devices


Pages 408 – 409 Figure 8-11

Automatic update automatically provides updates to the program



Booting – The process of loading or reloading the OS into the computer’s memory


The computer copies the kernel from the hard drive into the computer’s memory◦ The kernel

Is the central part of the OS Starts all applications Manages devices and memory Resides in memory at all times Performs other essential functions


Six steps to starting a computer:

Activate BIOS and Setup Program BIOS: Basic input/output system POST: Power on self-test

Sleep state: Transfers the current state of computer to RAM

Hibernate state: Saves battery power Hybrid sleep state: Combines sleep and hibernate

Account: User name, password, and allotted storage space

Multitasking operating systems: Permit more than one application to run at the same time and can manage multiple applications running simultaneously


Page 409


MS-DOS

WINDOWS XP MAC OS

LINUXUNIX


Windows 1.0 (1985)Windows 2.0 (1987)Windows 3.x (1990-1992)Windows NT (1993)Windows 95 (1995)Windows 98 (1998)Windows 2000 (2000)Windows ME (2000)Windows 7

Created in 1984

First OS to use graphical user interface

Easiest operating system for beginners

A new version, Mac OS X, was released in 2000


Developed for IBM PCs in 1981

Uses command-line interface

Use is diminishing


Developed by AT&T in 1970s

Developed concepts of file management and path names

Multitasking OS


Developed in 1991

Open-source code –Available for all to see and use

UNIX typed, More stable than Windows

Powerful and free

Growing acceptance


An embedded operating system resides on a ROM chip on a mobile device or consumer electronic device


Pages 418 - 420


Pages 419 – 420Figures 8-22 – 8-26

A utility program is a type of system software that allows a user to perform maintenance-type tasks



Backup software

Antivirus software

Disk scanning

Disk defragmentation

File compression

Etc.

A backup utility allows users to copy files to another storage medium

A restore utility reverses the process and returns backed up files to their original form

Discovering Computers 2012: Chapter 8 49


Antivirus software protects the computer from computer viruses



Pages 425 - 426


Pages 425 – 426 Figures 8-36 – 8-37


Page 426

Filters are programs that remove or block certain items from being displayed


Pages 426 - 427

Known as a file manager Enables the user to

perform various tasks on storage devices using files, folders, and directories

Tasks include:◦ Creating folders◦ Saving, deleting,

copying, and moving files and folders

◦ Examining the contents of files

◦ Launching application programs© Prentice-Hall, Inc

Search programs enable users to find files on storage devices


Computer startup failure◦ Use a boot disk (emergency disk) in the floppy

drive System slowdown

◦ Scan for viruses◦ Defragment the hard disk


A disk defragmenter reorganizes the files and unused space on a computer’s hard disk so that the operating system accesses data more quickly and programs run faster◦Defragmenting


Pages 423 – 424 Figure 8-32

A screen saver causes a display device’s screen to show a moving image or blank screen if no activity occurs for a specified time

A personal firewall detects and protects a personal computer from unauthorized intrusions


Page 425 Figures 8-34 – 8-35

A file compression utility shrinks the size of a file(s)◦ Compressing files frees up room on the storage

media◦ Two types of compression

Lossy Lossless

Compressed files sometimes are called zipped files◦ Can be uncompressed


Page 427

A media player allows you to view images and animation, listen to audio, and watch video files on your computer



Disc burning software writes text, graphics, audio, and video files on a recordable or rewritable optical disc



A personal computer maintenance utility identifies and fixes operating system problems, detects and repairs disk problems, and includes the capability of improving a computer’s performance



Archive: Single file that contains two or more files stored in a compressed format along with additional information

Windows Update: Keeps the operating system up to date with fixes; also called service packs

File compression utility: Enables the exchange of programs and data efficiently by reducing the size of a file

Safe mode: Operating mode in which Windows loads a minimal set of drivers known to function correctly

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