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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
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OS stays behind the scenes All software depends on the OS
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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
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Multiprocessing Multiprogramming Time-Sharing
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The use of a powerful computer with multiple CPUs
Multiple programs run simultaneously◦ Each runs on its own processor
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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
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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
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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
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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
© Prentice-Hall, Inc
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)
© Prentice-Hall, Inc
© Prentice-Hall, Inc
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
© Prentice-Hall, Inc
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
© Prentice-Hall, Inc
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
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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
© Prentice-Hall, Inc
Discovering Computers 2012: Chapter 823
Page 408
The user interface is that part of the OS with which the user interacts with a computer
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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
© Prentice-Hall, Inc
© Prentice-Hall, Inc
© Prentice-Hall, Inc
© Prentice-Hall, Inc
Operating systems typically provide a means to establish Internet connections
Discovering Computers 2012: Chapter 829
Page 408 Figure 8-10
A performance monitor is a program that assesses and reports information about various computer resources and devices
Discovering Computers 2012: Chapter 830
Pages 408 – 409 Figure 8-11
Automatic update automatically provides updates to the program
Discovering Computers 2012: Chapter 831
Page 409 Figure 8-12
Booting – The process of loading or reloading the OS into the computer’s memory
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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
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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
Discovering Computers 2012: Chapter 839
Page 409
© Prentice-Hall, Inc
MS-DOS
WINDOWS XP MAC OS
LINUXUNIX
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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
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Developed for IBM PCs in 1981
Uses command-line interface
Use is diminishing
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Developed by AT&T in 1970s
Developed concepts of file management and path names
Multitasking OS
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Developed in 1991
Open-source code –Available for all to see and use
UNIX typed, More stable than Windows
Powerful and free
Growing acceptance
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An embedded operating system resides on a ROM chip on a mobile device or consumer electronic device
Discovering Computers 2012: Chapter 846
Pages 418 - 420
Discovering Computers 2012: Chapter 847
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
Discovering Computers 2012: Chapter 848
Page 421 Figure 8-27
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
Page 424 Figure 8-33
Antivirus software protects the computer from computer viruses
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Discovering Computers 2012: Chapter 851
Pages 425 - 426
Discovering Computers 2012: Chapter 852
Pages 425 – 426 Figures 8-36 – 8-37
Discovering Computers 2012: Chapter 853
Page 426
Filters are programs that remove or block certain items from being displayed
Discovering Computers 2012: Chapter 854
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
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Computer startup failure◦ Use a boot disk (emergency disk) in the floppy
drive System slowdown
◦ Scan for viruses◦ Defragment the hard disk
© Prentice-Hall, Inc
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
Discovering Computers 2012: Chapter 8 58
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
Discovering Computers 2012: Chapter 8 59
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
Discovering Computers 2012: Chapter 860
Page 427
A media player allows you to view images and animation, listen to audio, and watch video files on your computer
Discovering Computers 2012: Chapter 861
Page 427 Figure 8-38
Disc burning software writes text, graphics, audio, and video files on a recordable or rewritable optical disc
Discovering Computers 2012: Chapter 8 62
Page 428 Figure 8-39
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
Discovering Computers 2012: Chapter 8 63
Page 428 Figure 8-40
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