OS

OPERATING SYSTEMSSoftware in the Background

Chapter 2

Objectives• Describe the functions of an Operating System

• Explain the basics of a personal computer operating system

• Describe the advantages of a graphical operating system

• Differentiate among different versions of Microsoft Windows

• Explain the need for network operating systems

• Describe the methods of resource allocation on large computers

• Be able to describe the differences among multiprocessing, multiprogramming, and timesharing

• Explain the principles of memory management

• List several functions typically performed by utility programs

Contents• Operating System: Hidden Software• Systems Software• Functions of OS• Types of OS

– MS-DOS– Microsoft Windows– Mac OS– UNIX– LINUX– Network Operating System NOS

• Resource Allocation• Utility Programs

Operating SystemHidden Software

• Definition – provides access to all resources• Kernel

– Manages the operating system– Memory resident– Loads set of programs that lies between applications

software and the hardware– Fundamental software that controls non-resident portions of

the OS as needed

• Booting – Loads the kernel into memory

Systems Software

• Definition:– All programs related to coordinating

computer operations

• Components– Operating System– Utility programs– Program language translators

Functions of OS

• Manage the computer’s resources– CPU– Memory– Disk drives– Printers

• Establish a user interface

• Execute and provide services for applications software

• Carries out all input and output operation

User Interface

• Facilitates communication between the user and the operating system

• Two forms– Command line

• Text-based• Key commands• Examples: MS-DOS, Unix

– Graphical user interface (GUI)• Visual images• Menus• Examples: Windows, Mac OS, Linux

Platform

• Definition:Computer hardware and operating system software that dictate what other software can run

• WintelIntel-based PC running Microsoft Windows

OS is Hidden

• User interested in application software to make the PC useful

• Application software is platform specific

• User must be aware of the type of OS

• User should be aware of the functions of OS

Types of OS

Command line

Single user PC

Network Operating System (NOS)

MS-DOS

• Command-line interface

• Prompt – system is waiting for you to do something

• Key a command

• Not user-friendly

Microsoft Windows

• Graphical user interface

• Eases access to the OS

• Most new computers come with Windows already installed

GUI

• On-screen pictures– Icons– Menus

• Pull down• Pop up

– Click to activate a command or function

• Fast• Easy• Intuitive

Early Days of Windows

Operating environment for MS-DOS

Shell – layer added between users and DOS

Windows Today

• Home/consumer market– Windows 95– Windows 98– Windows Millennium Edition (ME)

• Corporate market– Windows NT– Windows 2000

• Windows XP• Pocket computers and Internet appliances

– Windows CE

Windows 95 and 98• Self-contained OS

• DOS commands still available

• Start programs by– Start button– Double clicking the icon

• Task bar permits movement between open programs

• Long file names up to 255 characters

• Plug and play

• Object linking and embedding (OLE)

Windows 98 Additions

• Internet / intranet browsing

• Support for DVD and additional multimedia components

• Support for large hard drives

• TV viewer and broadcast ability

• Wizards

Improved Windows Features

• Backup

• Interfaces with other software

• Networking features

• Security

• Dr. Watson

Windows

Helps reduce the cost of owning and maintaining a PC

Windows MEMillennium Edition

Multimedia support -- Windows Media Player 7

• Jukebox– Record music CDs as digital files

• Windows Movie Maker– Basic video editing

• Windows Image Acquisition– Scanner and digital camera

Windows MEMillennium Edition

• Reliability Features– System File Protection– AutoUpdate– System Restore

• Help Center• Home Network Support

– Wizard for connecting multiple computers and peripherals

– Multiple users can share a single Internet connection

Windows NTNew Technology

• Engineered for stability• Strong security• Versions

– NT Workstation– NT Server

• Drawbacks– Lacks support for older Windows and MS-DOS

software and hardware– Complex to learn and use– Requires more memory and processing power

Windows 2000

• Stability features• Security features• Uses simple approach to hardware setup

from Windows 98• Versions

– Windows 2000 Professional for individual users– Windows 2000 for network servers

• Was intended for both the corporate and home use, replacing Win NT and Win 98

Windows 2000

• Complex

• Heavy demand for computer resources

• Improvements over windows NT– Maintains user preferences– Self-healing applications software– Supports Windows 98 file structure– Uses plug and play– Provides improved support for laptops

Windows XP

• Extends Windows ME and provides a more stable environment

• Two categories – Network server

• 3 versions based upon network complexity

– Desktop computer• 2 versions

– Professional Client – Personal Client

Windows CE Consumer Electronics

Where used• Embedded systems

– Industrial controllers– Robots– Office equipment– Cameras– Telephones– Home entertainment devices– Automobile navigation systems

• Pocket PC• Internet appliance market

Windows CE Consumer Electronics

Subset of Windows• Less memory

• Smaller screens

• Little or no file storage

• Provides Internet connectivity

Accessibility Options

• Seeing

• Hearing

• Touching

Mac OS

• First commercially successful GUI (1984)

• Served as a model to other GUI systems

UNIX

• Supports– Multi-user– Time-sharing

• Character-based system• Command-line interface• Runs on various processors and many

types of computers• Primary OS used on Internet servers

LINUX

• UNIX-like OS• Open-source software

– Download it free– Make changes– Distribute copies– Restriction – any changes must be freely available to the

public

• PC Setup– PC comes with Windows installed– Install LINUX in a dual-boot configuration

LINUX

• Advantages over Windows– Extremely stable– Internet support– Reinstallation is simpler

• Disadvantage– Scarcity of applications

Network Operating System NOS

• Designed to permit computers on a network to share resources

• Examples– Windows 2000 Server– Novell Net Ware

• Provides– Data security– Troubleshooting– Administrative control

NOS Functions

• Split between client and server computers• Server

– File management

• Client– Requests to the server– Messaging– Has own local OS

• Makes the resources appear as if they are local to the client’s computer

Large Computers

• Used by many people at once

• OS works “behind the scenes” so users can share

• OS must control– Who gets access to resources– What keeps the programs from different

users from getting mixed up with one another

Resource Allocation

• Resource – hardware or software that is needed to complete a task

• Resource Allocation – assigning computer resources to certain programs

• Resource De-allocation – releasing resources when a task is complete

Allocating the CPU

• One CPU– Multiprogramming

• Event-driven• Timesharing

• More than one CPU– Multiprocessing – multiple CPUs can run

several programs simultaneously

Multiprogramming

• One CPU

• Concurrent execution of two or more processes– Several processes open at once– Only one process can receive the attention

of the CPU at any given moment– Effective because CPU speeds are many

times faster than input/output speeds

Event-driven Multiprogramming

• One program receives the attention of the CPU

• Its processing will be interrupted based upon events in the program

• When processing needs to be temporarily suspended, an interrupt is generated

• This is a signal to the operating system to evaluate the cause of the interrupt and determine who should now have CPU time

Event-driven Multiprogramming Example

• Two programs are running – Payroll and Inventory Management

• Payroll needs to read an employee record

• Payroll generates an interrupt

• Normal processing is temporarily suspended

• The CPU looks at the interrupt and initiates the read operation

• While waiting for the read to complete, the CPU begins processing the Inventory Management program

Event-driven Multiprogramming Example

• When the read operation is complete, another interrupt is generated

• Normal processing is temporarily suspended

• The CPU looks at the interrupt and determines its cause

• The CPU will either continue processing the Inventory Management program or return to the Payroll program depending upon their priority

Time-sharing Multiprogramming

• One program receives the attention of the CPU

• A small fraction of CPU time is allocated to the program

• The time slice ends

• The CPU begins processing a different program

• Response time can vary based upon the number of users on the system

Sharing Memory

• Program must be in memory to be executed

• Problems– Programs compete for space– May have a very large program– Memory space for each program must not

overlap

Memory Management

• The process of providing separate memory space to programs

• Memory Protection keeps one program from interfering with another

Memory ManagementMethods

Partitions or regions

Foreground and background

Virtual storage (virtual memory)

Partitions or Regions

• Divide memory into sections

• The partition must accommodate the largest possible program

• Problem– May cause wasted memory space

Foreground and Background

• Programs are placed in either Foreground or Background

• Programs in Foreground have priority for CPU time

• While performing read / write operations for the Foreground program, the CPU gives time to a program in Background

• Programs are placed in a holding queue while waiting to run

Virtual StorageVirtual Memory

Uses concept of Paging

• Divide the program into equal-size pieces (pages)

• Store each piece in equal-size memory spaces (page frames)

• Typical size is 2KB or 4KB

• Create an index to each page and store in a Page Table

Paging Process

• A portion of the program is placed in memory

• The remainder is on disk

• Sections on disk will be brought into memory as needed (one page at a time)

Virtual StorageVirtual Memory

Virtual StorageVirtual Memory

• Problem -- Thrashing– Too large a portion of CPU time is spent

locating the correct page and bringing it into memory

• Solution– Run fewer programs concurrently– Add memory

Memory Protection

• Keeps one program from straying into another• Confines each program to certain defined

limits in memory• Why needed

– Possible for one program to destroy or modify another by transferring to the wrong memory location

– May cause destruction of data

• Action if assigned memory space is violated– Termination of executing program

Sharing Storage

• Several users need to access the same disk pack– One wants to write– Another wants to read

• OS keeps track of the I/O requests

• OS processes I/O requests in order received

Sharing Printing Resources

• Print resources are shared between active programs

• Printouts are generated in pieces as the CPU gives each concurrent program some time

• Problem– The current program may generate a few print

lines– The CPU moves to the next program– The second program may generate a few print

lines, etc.

Sharing Printing Resources

• Result– Printout is worthless as it contains a few lines from

several programs

• Solution – Spooling– Each program thinks it is writing to the printer– The program actually writes to the hard disk– When the program is complete, the file on the hard

disk is sent to the printer

Additional Printing Problem

• Printers are slow compared to the CPU speed

• Solution– The CPU writing to the disk– The program completes quicker

Utility Programs

• Come with System Software• Handle special needs• Perform secondary chores• Do not need to be memory resident

Functions of Utility programs

• File manager – provide access to lists of stored files• Backup and Restore – make duplicate copies of

important files and return the copy to the hard drive if needed

• File compression – reduces the amount of disk space required by a file

• Disk defragmenter – reorganize files so they are stored contiguously on disk providing for faster access

• Device drivers – convert operating system instructions into commands that are known to a specific device