chapter 1 part 3-mod

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CHAPTER 1OPERATING SYSTEM ENVIRONMENT

PART 3

Chapter 1 Part 3

FP202 Fundamentals of OperatingSystem

FP202 Fundamental of OS


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CHAPTER SUMMARY

a) Concept in operating system

b) Components of operating system

c) Different interfaces of operating system

d) Relations between system calls and ApplicationProgramming Interface (API)


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a) Concept in

Operating System


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1) MULTITASKING

Process of letting the operating system perform multiple taskat what seems to the user simultaneously.

The CPU switches from one program to the next so quicklythat appears as if all of the programs are executing at thesame time.

System with multiple processor

- This is the case, since there are several CPU's to executeprograms on .

System with single processor

- Multitasking done by switching execution very rapidlybetween each program, thus giving the impression of

simultaneous execution.-This process is also known as task switching or timesharing.


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2) MULTIPROGRAMMING

Goal of multiprogramming is to efficiently utilize all of thecomputing resources.When a job issues an I/O request (e.g., open a file, read datafrom a file), it cannot continue until the request is fulfilled.The CPU then becomes idle (the job is blockedon therequest).


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3) TIME SHARING

Logical extension of multiprogramming termed multitasking.

Quite often sitting at terminal using a command line interfaceto interact with computer.

Types in commands from keyboard.

A system program called a shell reads command from thecommand line and makes OS system calls to carry outcommands.

Switching between users is very fast.

Goal is to give the illusion that each user has own machine.


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4) BUFFERING

Buffering is a method of overlapping the computation ofa job with its execution.

It temporarily stores input or output data in an attemptto better match the speeds of two devices such as a fastCPU and a slow disk drive.

If, for example, the CPU writes information to the buffer,it can continue in its computation while the disk drivestores the information.


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5) SPOOLING

FP202FundamentalofOS

With spooling, the disk is used as a very large buffer. Usually

complete jobs are queued on disk to be completed later.

A typical example is the spooler for a printer. When a print job is

issued, the spooler takes care of it, sending it to the printer if it is notbusy, or storing it on disk otherwise.


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OPERATING

SYSTEM

COMPONENTS



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Operating system comprises a set of software packages thatcan be used to manage interactions with the hardware.

The following elements are generally included in this set ofsoftware:

1) Kernel

- Represents the operating systems basic functions such as

management of memory, processes, files, main inputs/outputsand communication functionalities.

2) Shell

- Allowing communication with the operating system via acontrol language, letting the user control the peripherals

without knowing the characteristics of the hardware used,management of physical addresses, etc.



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3) File System

- Allowing files to be recorded in a tree structure.

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OPERATING

SYSTEM

INTERFACES

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USER INTERFACE

A user interface is the system by which people(users) interact with a machine. The user interfaceincludes hardware (physical) and software (logical)components.

User interfaces exist for various systems, andprovide a means of:

- Input, allowing the users to manipulate a system,and/or

- Output, allowing the system to indicate the effectsof the users' manipulation.

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USER INTERFACE

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Users may also interact with theoperating system with some kindof software user interface liketyping commands by usingcommand line interface (CLI) orusing a graphical user interface.

For hand-held and desktopcomputers, the user interface isgenerally considered part of theoperating system.

On large multi-user systems such

as Unix-like systems, the userinterface is generally implementedas an application program thatruns outside the operating system.

Operating System Placement


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COMPONENTSOFTHE USER INTERFACE

The user interface has two main components:

Presentation language, which is the computer-to-human part of the transaction.

Action language that characterizes the human-to-

computer portion.

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TYPESOF USER INTERFACES

There are several types of user interfaces: Command Line Interfaces.

Menu interfaces.

Graphical User Interfaces (GUIs).

Voice User Interfaces. Web Form Interfaces.

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1) COMMAND-LINE INTERFACE

CLI are often used by programmers and systemadministrators, in engineering and scientificenvironments, and by technically advancedpersonal computer users.

Examples of CLI application:

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2) MENU INTERFACES

Menu Interface presents user with a menu ofchoices.

Rather than learning specific commands, userchoose them from the menu.

Menus can contain submenus, in which case userneed to memorize how to access a particularcommand.

This is still much easier than memorizing the actualcommand.

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MENU INTERFACE

Menu interfaces commonly appear the beginning of agame, often at the title screen regardless of how menusare used later in the game.

Past the opening menu, games often provide an optionmenu for saving. While these examples constitute menuinterfaces, many games include menu interfaces tocontrol entity actions as well.

Some games provide a series of menus through whichthe player controls game entities that is analogous tomenu systems found in interactive kiosks.

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MENU INTERFACE

The sophistication of these menu interfaces ranges fromsimple, flat menus to deeply nested menus with manysub-options.

The specific representation of menu interfaces can varyas well, some games representing menus as a series ofgraphical buttons, others using text menus.

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MENU INTERFACE

Menu interface provides the user with an onscreenlist of available selections.

A nested menu is a menu that can be reachedthrough another menu.

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3) GRAPHICAL USER INTERFACE (GUI)

A graphical user interface or GUI (sometimespronounced gooey) is a type of user interface itemthat allows people to interact with programs in moreways than typing such as computers

Examples: hand-held devices such as MP3Players, Portable Media Players or Gamingdevices; household appliances and officeequipment with images rather than text commands.

A GUIoffers graphical icons, and visual indicators,

as opposed to text-based interfaces, typedcommand labels or text navigation to fully representthe information and actions available to a user.

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GRAPHICAL USER INTERFACE (GUI)

The actions are usually performed through directmanipulation of the graphical elements.

Pictures tend to make the interface more intuitive.FP202Fun

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GUI CHARACTERISTICS

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Characteristic Description

Windows Multiple windows allow different information to bedisplayed simult aneously on the users screen.

Icons Icons different types of information.On some syst ems,

icons represent files; on others, icons representprocesses.

Menus Commands are select ed from a menu rat her than t ypedin a command language.

Point ing A point ing device such as a mouse is used for select ingchoices from a menu or indicating it ems of in terestin a

window.Graphics Graphical elements can be mixed with text on the same

display.


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4) VOICE USER INTERFACE

A Voice User Interface (VUI) makes humaninteraction with computers possible through avoice/speech platform in order to initiate anautomated service or process.

The VUI is the interface to any speech application. Controlling a machine by simply talking to it was

science fiction only a short time ago.

However, with advances in technology, VUI havebecome more common place, and people aretaking advantage of the value that these hands-free, eyes-free interfaces provide in manysituations.

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VOICE USER INTERFACE

Voice User interface are developing rapidly

There are two different types of voice recognition: Continuous speech systems, allowing for dictation.

Speaker independence, so people can enter commands

or words at a given workstation.

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5) WEB FORM INTERFACES

Web Form interfaces are onscreen forms displayingfields containing data items or parameters thatneed to be communicated to the user.

Web Form interfaces may be implemented using

the Web.

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WEB FORM INTERFACES

A Web Form allows a user to enter data that is sentto a server for processing.

Web forms resemble paper forms because internetusers fill out the forms using checkboxes, radiobuttons, or text fields.

For example, Web Forms can be used to entershipping or credit card data to order a product orcan be used to retrieve data (e.g: searching on asearch engine).

In addition to functioning as input templates for newinformation, Web Forms can also be used to queryand display existing data in a similar manner to mailmerge forms, with the same advantages.

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WEB FORM INTERFACE

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Title

Author

Publisher

Edition

Classification

Date ofpurchase

ISBN

Price

Publicationdate

Number ofcopies

Loanstatus

Orderstatus

NEW BOOK


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RELATION

BETWEENSYSTEM CALLS

AND API

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SYSTEM CALLS

User programs are not allowed to access system resourcesdirectly. They must ask the OS to do that for them.

OS provides a set of functions that can be called by userprograms to request for OS services. These functions arecalled system calls

System calls run in kernel mode.

They can be called by executing a special instruction (trap orsoftware interrupt) which causes processor to switch to thekernel mode and jump to a previously defined location in thekernel.

When the system call finishes, processor returns to the userprogram and runs in user mode.

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APPLICATION PROGRAMMING INTERFACE (API)

An API is a set of functions provided by an operating

system or other system software.

An application program calls the functions to request the

services. An API clearly defines how to call functions and what the

results are. (API is specification, not implementation)

Examples: APIs for file system, graphics user interface,

networking, etc.

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APPLICATION PROGRAMMING INTERFACE (API)

Portability User programs that follow the APIs definition are portable.

An API can provide a common interface for differentimplementations of a service.

For example, the UNIX file system API is the same for allkinds of devices.

X windows API has many implementations on differentmachine architectures

Using an API allows upgrading system software withoutchanging user programs

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