TyroCity: Computer 11 Notes

Input Devices

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Some of the input devices used in a computer are keyboard, mouse scanner, joystick, touch screen, touchpad, track ball, bar code reader, light pen, optical code reader (OCR), MICR, OMR, microphone, digital camera, webcam, card readers, digitizing tablets, etc.

Keyboard

Keyboard is the most basic input device. It is used for text input. It contains multiple keys. User can provide input by pressing the key. The different types of key found in keyboard are:

Alphanumeric keys (A-Z, 0-9)
Function keys (Ctrl, Alt, Caps lock, Enter, Tab, Shift)
Special function keys (F1, F2, F3,……..,F12)
Cursor movement keys (?, ?)
Punctuation keys (,, “” , ’’, ?, !)
Numeric pad
Multimedia keys

On the basis of keys, keyboard can be classified as

XT keyboard -83 keys
AT keyboard -101 keys
Enhanced keyboard -103 and more keys

A keyboard contains an electronic circuit known as keyboard encoder. This circuit detects the pressed key, generates its electronic signal and transmits towards CPU.
On the basis of connectivity, keyboard can be wire or wireless.

Mouse

Mouse is a most common pointing and selecting device. It is used in graphical user interface. Mouse contains buttons for providing inputs. User can provide inputs by moving the mouse and pressing the button. On the basis of buttons, mouse can be:

Two-buttoned mousse
Three-buttoned mouse

Usually, the left button of the mouse is for normal selection and the right button is used for special function and central button is used for scrolling a document.
On the basis of working mechanism and its architecture, mouse can be classified as:

Mechanical mouse
Opto-mechanical mouse
Optical mouse

Mechanical mouse contains a rubber ball and a pair of rotating wheels. When the mouse is moved on the table, the ball rotated which results in rotation of the wheels and generates electronic signal.
Optical mouse operates using reflection of light. It is easier to use but usually less reliable than mechanical mouse.
The opto-mechanical mouse contains both mechanical and electric component.

Track ball
Trackball is the modification of mechanical mouse. It contains rubber ball on its top. User can move the cursor by rotating the ball with finger. It also contains two buttons on the either sides similar to mouse. It was used in older laptops.

Track pad/Touch pad

Track pad is the modification of optical mouse, and touch pad is further modification making it touch sensitive. It contains a window with two buttons on the either sides. User can also provide left click option by tapping the window with the finger. It is mainly used in portable devices like laptops, notebook, palmtop, etc.

Joystick

Joystick is a hand held pointing device which is mainly used for playing games. It is used for controlling objects, their movement, direction and speed of movement. Modern joysticks handle can move in any direction. When the handle is moved, the electronic circuit in the base detects the movement and sends corresponding binary signals to CPU.

Light pen

Light pen is used for creating drawings, designs by directly touching the screen. It is mainly used by designers, architects, engineers, etc. it is used in monitor not having touch screen facility. It is a pen shaped structure containing photo sensitive tip which can capture light emitted from the monitor and mark the position on the monitor.

Touch screen

Touch screen is none of the common input device at present mainly for portable computers. User can provide inputs by directly touching the screen with the metallic pen (stylus), finger or any pointed object. Touch screen is developed by using either of the following technologies:
a) Pressure sensitive
b) Capacitive
c) Infrared

Scanner

Scanner digitizes hard copy or printed images which can be used in digital computers. Scanner copies the image and draws a new digital image in its memory similar to hard copy image.

OCR (Optical Character Reader)

OCR digitizes handwritten or printed text.
Printed text will have fewer errors than hand written. It directly converts hand written text into digital text which can be edited. OCR contains predefined format of all the characters. During digitizing process, it creates an image of the character and compares it with stored format to determine the character.

MICR

It stands for Magnetic Ink Character Reader. MICR is an OCR that can digitize text written or printed by using magnetic ink like iron oxide or barium ferrite. It is used in security systems and for processing cheque in bank.

OMR

It stands for Optical Mark Reader. It is used for answer sheet correction in multiple choice questions. With the use of OMR answer sheet correction will be faster and error free.

BCR

It stands for Bar Code Reader. Bar codes are the magnetic lines used for storing the information about the product like manufacturing date, expiry date, company name, etc. BCR is used to read the information stored in bar codes. Bar codes are also used in security system.

Microphone

It is an input device for sound. It captures sound wave, converts it into digital format and provides it to the CPU. Common mobile computing devices like PDA, smart phone contains microphone.

Digital camera, Web camera

Digital camera captures real time images and video and stores it in a digital format. The image captured by digital camera can be directly used in a digital camera.

Web camera is a digital camera used in internet. It usually captures low quality images so that it could be transmitted at a faster speed.

Card reader

It is used to read the information stored in cards like ATM card, Credit card, Smart card, etc.

Digitizing tablet

It is used to digitize large map or hardcopy images. It is also used to track the movements of living beings and capture them in digital format.

Introduction To Windows 3.1

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction to windows 3.1

If somebody buys a new computer today, it will probably come loaded with Windows. It is a Graphical User Interface (GUI) program meant for IBM compatible PCs. It provides the flexibility of using graphical icons and work interactively with the computer. One doesn’t need to remember operating system commands and type them. He just has to move the small mouse arrow key, known as mouse pointer around the screen (better known as window) and select the require command by pressing the click button. Each window, which represents programs, can be resized and moved around the screen. Multiple windows can appear on the screen at the same time giving user the flexibility of operating more than one program.

Objectives

At the end of this lesson you would be able to:

Understand the concept of windows working environment
Differentiate between confessional character display Interface and graphical user interface.
Explain about various features of Windows
Understand various Icons and their functions.

Types of windows and icons

Before using Windows effectively, it is very essential to understand the concept of window type and Icons used in Windows. The entire screen is termed as Windows Desktop, on which all windows are displayed. It is same as that of laying all your work on the surface of your working table. Here the working table is the Windows Desktop and all your work is individual windows on the desktop.
In general, there are two types of windows and three types of Icons which window uses. The window types are:

Application windows, which displays the executable windows program in GUI mode. These windows can be, opened, closed, resized and moved around the screen or the desktop.
The other type of windows is a document window, which are generated by the executable or application program. These document windows cannot be sized or moved outside the limit of its parent application windows.

Windows uses three types of icons, namely application, document and program icons.

Application icons are the minimized version of the currently running application program. This icon appears at the bottom of the desktop and can be maximized.
Document icons are the reduced document windows. When maximized, it appears within an application window’s workspace.
Program icons that appear within Program Manager and clicking on these icons activate the associated applications and also load the related documents or files.

Parts of windows

All most all windows have common components. The components are:

Title Bar
Buttons for Minimize, Maximize and Restore
Borders for Resizing
Menu bar and Pull-down menus
The scroll bar

1. Title bar
Title bar is displayed in color at the top of the windows. It contains the name, or the title of the current windows. The windows can be moved around the window desktop using this title bar.

2. Buttons for Minimize, Maximize and Restore
These buttons are displayed at the top-right corner of the screen. As the name suggests, minimize button is used to reduce the current windows into an applications icon, which will appear at the bottom of the windows desktop.
Similarly, maximise button is used to expand the current windows to take up the entire desktop.
Restore button is used to restore the state of the windows, where it was before maximization.

3. Borders for resizing
A thin border appears around the windows, which can be used to resize the current windows. To resize the current windows, just place the pointer on the border (this will become two-headed arrow «) of the windows, click the mouse button, hold and drag to the desired location. The windows will change its size. Vertical and Horizontal borders can be used to change the width and height of the windows respectively, while corner border can be used to change width and height simultaneously.

4. Menu bar and pull-down menus
Menu bar is located under the Title bar and contains the related Pull-down menus for the currently active windows. Clicking on a menu name will activate a pull-down menu with various options to select.

5. The scroll bar
When the active windows cannot accommodate the data to be displayed then it provides a scroll bar that helps to move through the data. Vertical scroll bar allows to view data by moving up or down through a document, whereas horizontal bar allows the movement from left to right. The vertical scroll bar appears on the right side of the active windows and horizontal scroll bar at the bottom.

Windows dialogue boxes
While using application program in window, sometimes it is require to change the settings within a program for example default margin the a word processing document, default printer, font type and size etc. All these are accomplish by window’s dialog box, which appear when the menu with an ellipsis (..) beside it is activated. It is basically serve two purposes one that it allows to change/rest the parameters related to currently running application and displays information such as warnings, error message etc. The displayed dialog box may contain the followings:

1. Command button
This button activates an action. The most commonly used command buttons are OK and CANCEL. Command buttons with an ellipse (..) indicate a link to another dialog box.

2. Check box
Check box allows selecting one or more option from a list of options. When selected an X appears besides the option selected and the corresponding option becomes active.

3. List Box
List box displays a series of options available in a column. To select an item, move the mouse pointer to the item and click on it. If the number of items is more than the height of the list box, then it provides a scroll bar to move through the entire range of items in the list box.

4. Option Buttons
It has the same features as that of check box. It allows selecting an option in a list of choices. When selected, the small hollow circle gets filled. Once an option gets selected from the available set of options, other options automatically get deselected.

Disk space required

Microsoft Windows along with MS-DOS version 6.0 requires a minimum of 15.8 MB and maximum of 18.3 MB of free disk space. Minimum disk space assumes no optional components, network or printer settings. However maximum disk space includes all installable components, network and printer.

Windows vs. Microsoft-DOS

Windows provides tools to accomplish all the tasks in case of file and directory management as in MS-DOS. The main difference is how the work is done. Rather than remembering all the commands and typing them at the DOS prompt, in Windows one can move the mouse pointer to the required command, and windows will execute the command. Windows supports all the File and Directory management commands of MS-DOS and it also supports Microsoft-DOS conventions in working with files such as wild card characters.

Windows programs

In this section, programs provided in windows such as program Manager, File manager etc. are discussed. These are vital part of windows operating environment and one must know how to work and use these programs.

1. Program Manager
When window program starts Program manager is the first windows displayed on the window desktop. The only way to leave windows is to closing or exiting this program manager. Within Program Manager there is some secondary window known as group windows, which appears as fully opened window such one with title ‘Main’ or as group icons, which appears at the bottom of ‘Main’ windows. A group icon is a group window, which can be minimized. Group windows contains logically related programs, such as one group windows can contain all programs associated with database while another may be for word processing.
There are five default groups in Windows. They are;
Main group of windows contain all the system applications: File manager, Print Manager, MS-DOS prompt, Windows Setup and PIF Editor.

Applications group consists of all the application found on your hard disk, while installing the windows. How ever if, during installation process if you chose the Custom Setup option and chose not to have Windows set up applications from your hard disk, the program manager will not contain an Application group.
Accessories group is made of windows based applications for word processing (Write), drawing (Paint), communications (Terminal), plus several other useful applications.
Games group contains windows based games.
Start Up group has application that loaded when windows system starts initially. Any applications can be added to this group. This group remains empty until, an application is added to it.

Windows provide the flexibility to install other group windows also.
Group windows can be resized, moved and it contains the icons for the program, which can be executed. Program items can be added deleted in-group windows and they can be copied between group windows also.
However neither the group windows can be moved outside the program manager nor the group icons. By selecting the icons, one can run the associated program files. All the program items can be moved between groups copied or renamed.

2. File manager
As the name suggests, File manager is used to manage or manipulate both disk and the disk files. It provides visual representations of all disks and disk files in the system.
As displayed in the above figure, the directory structure for the hard disk of the system and all the files in the current directory, appear in a document windows, known as directory window. The attributes of one or more file can be changed, by selecting them from the directory window. They can also be moved between directories, or opened, renamed, printed, deleted or copied.

1. Selecting File(s) and directories

File Manager allows you to select one or more than one files at a time for copying, moving or deleting or to perform other related task.
To select a file or directory clicks the desired icon. Or press the TAB button to move to the list of files, and then use the direction keys or arrow keys to select.
To select consecutive files, select the first file, press and hold down the SHIFT key, and then click the last file on the desired file list or group. Alternatively, select the first file, press and hold down the shift key and then use arrow keys to extend the selection to the last item in the group.
To select or cancel selection of the non-consecutive files, press and hold ctrl key and click on each file. Alternatively, press SHIFT and F8 key, use arrow keys to move to each file, use spacebar to select the file or to cancel already the selected file, then press shift and f8 again.
To select similar type of file, activate the Select Files option from the File menu bar. In the text box of the dialog box specify the type of files to be selected. For example *.doc to select all files in the current directory that has .doc as extension or secondary name.

In-text questions 1

1. State True or False.

File Manager is used to start Windows.
Group windows and group icon can be moved out of Program Manager
File maintenance is done using File manager in windows.
To activate a program when windows starts, you need to add it to File manager.
Print manager and File Manager are available in Games windows.

What you have learnt
In this lesson you were introduced to the concept of windows working environment and graphical user interface. It also discussed various features and components of windows. It explained with examples the icons and their functions. This also discussed how to select files and directories.

Terminal questions

Briefly discuss why Windows is popular.
Briefly explain about different components of windows and how to start windows.
How a group icon is different from individual program Which group programs are loaded when windows starts-up?
Can a DOS based application be used in Windows?

Feedback to in-text questions

False
False
True
False
False

Computer Science HSEB-XI 2069

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Computer science (HSEB-grade XI)-2069 (2012)
Candidates are required to give their answers in their own words as far as practicable. The figures in the margin indicate full marks.

Full Marks:- 75
Pass Marks:- 27
Time:- 3hrs.

Group ‘A’
Long answer questions
Attempt any three questions. 3×10=30
1. What is an operating system? Explain the functions of operating system.
2. What is memory in the computer system? Explain primary and secondary memory.
3. What is programming? Differentiate between compiler and interpreter.
4. What is Boolean algebra? Describe AND gate, OR gate, NOT gate and NAND gate symbol and Truth Table.

Group ‘B’
Short answer questions
Attempt any nine questions. 9×5=45
5. Why computer is known as versatile and diligent device? Explain.
6. What is mobile computing? Explain.
Or
Differentiate between analog and digital computer.
7. Convert (110111101)2 binary number into octal number.
8. What is BUS in terms of computer architecture? Explain.
9. Differentiate between Impact and Non-impact printers with examples.
10. What is internet? Write down the uses of internet.
Or
Explain the features of word processor.
11. What is web page? List the features of web page.
Or
Write down the advantages and disadvantages of DBMS. (Old)
12. What is CPU? Write down the functions of CPU.
13. Explain the types of programming errors with examples.
14. Subtract (1100)2 from (1111)2 using 1st and 2nd complement method.
15. Write short notes on:

Modem
Trackball

Memory

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Memory is mainly divided into two types. They are:

Classification of Memory

Language/Software

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Introduction

In the previous lesson we discussed about the different parts and configurations of computer. It has been mentioned that programs or instructions have to be fed to the computer to do specific task. So it is necessary to provide sequence of instructions so that your work can be done. We can divide the computer components into two major areas, namely, hardware and software. Hardware is the machine itself and its various individual equipment. It includes all mechanical, electronic and magnetic devices such as monitor, printer, electronic circuit, floppy and hard disk. In this lesson we will discuss about the other part, namely, software.

Objectives

After going through this lesson you will be able to

explain the concept of software
distinguish between different types of software
differentiate application software from system software
define a language
differentiate between different types of language
distinguish between compiler and interpreter

What is software?

As you know computer cannot do anything without instructions from the user. In order to do any specific job you have to give a sequence of instructions to the computer. This set of instructions is called a computer program. Software refers to the set of computer programs, procedures that describe the programs, how they are to be used. We can say that it is the collection of programs, which increase the capabilities of the hardware. Software guides the computer at every step where to start and stop during a particular job. The process of software development is called programming.

You should keep in mind that software and hardware are complementary to each other. Both have to work together to produce meaningful result. Another important point you should know that producing software is difficult and expensive.

Software types

Computer software is normally classified into two broad categories.

Application Software
System software

Application software: Application Software is a set of programs to carry out operations for a specific application. For example, payroll is an application software for an organization to produce pay slips as an output. Application software is useful for word processing, billing system, accounting, producing statistical report, analysis of numerous data in research, weather forecasting, etc. In later modules you will learn about MS WORD, Lotus 1-2-3 and dBASE III Plus. All these are application software.

Another example of application software is programming language. Among the programming languages COBOL (Common Business Oriented Language) is more suitable for business application whereas FORTRAN (Formula Translation) is useful for scientific application. We will discuss about languages in next section.

System software: You know that an instruction is a set of programs that has to be fed to the computer for operation of computer system as a whole. When you switch on the computer the programs written in ROM is executed which activates different units of your computer and makes it ready for you to work on it. This set of program can be called system software. Therefore system software may be defined as a set of one or more programs designed to control the operation of computer system.

System software are general programs designed for performing tasks such as controlling all operations required to move data into and out of the computer. It communicates with printers, card reader, disk, tapes etc. monitor the use of various hardware like memory, CPU etc. Also system software are essential for the development of applications software. System Software allows application packages to be run on the computer with less time and effort. Remember that it is not possible to run application software without system software.

Development of system software is a complex task and it requires extensive knowledge of computer technology. Due to its complexity it is not developed in house. Computer manufactures build and supply this system software with the computer system. DOS, UNIX and WINDOWS are some of the widely used system software. Out of these UNIX is a multi-user operating system whereas DOS and WINDOWS are PC-based. We will discuss in detail about DOS and WINDOWS in the next module.

So without system software it is impossible to operate your computer.

In-text questions 1

1. What are program, programming and software?

2. Differentiate between system software and application software.

3. Write True or False

The set of instructions given to the computer is called programming.
Application Software is a set of programs to carry out operations for a specific application.
UNIX is a multi-user operating system.

What is language?

You are aware with the term language. It is a system of communication between you and me. Some of the basic natural languages that we are familiar with are English, Hindi, Oriya etc. These are the languages used to communicate among various categories of persons. But how you will communicate with your computer. Your computer will not understand any of these natural languages for transfer of data and instruction. So there are programming languages specially developed so that you could pass your data and instructions to the computer to do specific job. You must have heard names like FORTRAN, BASIC, COBOL etc. These are programming languages. So instructions or programs are written in a particular language based on the type of job. As an example, for scientific application FORTRAN and C languages are used. On the other hand COBOL is used for business applications.

Programming languages

There are two major types of programming languages. These are Low Level Languages and High Level Languages. Low Level languages are further divided in to Machine language and Assembly language.

Low Level Languages

The term low level means closeness to the way in which the machine has been built. Low level languages are machine oriented and require extensive knowledge of computer hardware and its configuration.

Machine Language

Machine Language is the only language that is directly understood by the computer. It does not needs any translator program. We also call it machine code and it is written as strings of 1’s (one) and 0’s (zero). When this sequence of codes is fed to the computer, it recognizes the codes and converts it in to electrical signals needed to run it. For example, a program instruction may look like this: 1011000111101

It is not an easy language for you to learn because of its difficult to understand. It is efficient for the computer but very inefficient for programmers. It is considered to the first generation language. It is also difficult to debug the program written in this language.

Advantage

The only advantage is that program of machine language run very fast because no translation program is required for the CPU.

Disadvantages

It is very difficult to program in machine language. The programmer has to know details of hardware to write program.
The programmer has to remember a lot of codes to write a program which results in program errors.
It is difficult to debug the program.

Assembly Language

It is the first step to improve the programming structure. You should know that computer can handle numbers and letter. Therefore some combination of letters can be used to substitute for number of machine codes.

The set of symbols and letters forms the Assembly Language and a translator program is required to translate the Assembly Language to machine language. This translator program is called `Assembler‘. It is considered to be a second-generation language.

Advantages:

The symbolic programming of Assembly Language is easier to understand and saves a lot of time and effort of the programmer.
It is easier to correct errors and modify program instructions.
Assembly Language has the same efficiency of execution as the machine level language. Because this is one-to-one translator between assembly language program and its corresponding machine language program.

Disadvantages:

One of the major disadvantages is that assembly language is machine dependent. A program written for one computer might not run in other computers with different hardware configuration.

In-text questions 2

1. What is the difference between FORTRAN and COBOL?

2. Differentiate between machine language and Assembly language.

3. Write True or False

Low level language and High level language are two major types of programming languages.
Machine language is the only language that is indirectly understood by the computer.
Assembly language is second generation language.

High level language

You know that assembly language and machine level language require deep knowledge of computer hardware where as in higher language you have to know only the instructions in English words and logic of the problem irrespective of the type of computer you are using.

Higher level languages are simple languages that use English and mathematical symbols like +, -, %, / etc. for its program construction.

You should know that any higher level language has to be converted to machine language for the computer to understand.

Higher level languages are problem-oriented languages because the instructions are suitable for solving a particular problem. For example COBOL (Common Business Oriented Language) is mostly suitable for business oriented language where there is very little processing and huge output. There are mathematical oriented languages like FORTRAN (Formula Translation) and BASIC (Beginners All-purpose Symbolic Instruction Code) where very large processing is required.

Thus a problem oriented language designed in such a way that its instruction may be written more like the language of the problem. For example, businessmen use business term and scientists use scientific terms in their respective languages.

Advantages of High level languages

Higher level languages have a major advantage over machine and assembly languages that higher level languages are easy to learn and use. It is because that they are similar to the languages used by us in our day to day life.

Compiler

It is a program translator that translates the instruction of a higher level language to machine language. It is called compiler because it compiles machine language instructions for every program instructions of higher level language. Thus compiler is a program translator like assembler but more sophisticated. It scans the entire program first and then translates it into machine code.

The programs written by the programmer in higher level language is called source program. After this program is converted to machine languages by the compiler it is called object program.

Higher level language

———————————- ® (Compile) ® Program Machine Language Program

A compiler can translate only those source programs, which have been written, in that language for which the compiler is meant for. For example FORTRAN compiler will not compile source code written in COBOL language.

Object program generated by compiler is machine dependent. It means programs compiled for one type of machine will not run in another type. Therefore every type of machine must have its personal compiler for a particular language. Machine independence is achieved by using one higher level language in different machines.

Interpreter

An interpreter is another type of program translator used for translating higher level language into machine language. It takes one statement of higher level languages, translate it into machine language and immediately execute it. Translation and execution are carried out for each statement. It differs from compiler, which translate the entire source program into machine code and does involve in its execution.

The advantage of interpreter compared to compiler is its fast response to changes in source program. It eliminates the need for a separate compilation after changes to each program. Interpreters are easy to write and do not require large memory in computer. The disadvantage of interpreter is that it is time consuming method because each time a statement in a program is executed then it is first translated. Thus compiled machine language program runs much faster than an interpreted program.

In-text question 3

1. What is the difference between interpreter and compiler

2. Give some examples of high level language.

3. Write True or False

High level languages are problem-oriented language.
Object program generated by compiler is machine independent.
The disadvantage of interpreter is that it is time consuming.

What you have learnt

In this lesson we discussed about two types of software, namely, system software and application software. System software controls the hardware part of the computer. It is designed for performing tasks such as controlling all operations required to move data into and out of the computer. It communicates with printer, card reader, disk, tapes, etc. and monitors the use of various components like memory, CPU, etc. DOS, Unix and Windows are three important system software. Application software is a set of programs written for specific purpose. Examples of application software are Microsoft Word, Lotus 1-2-3, COBOL, BASIC and FORTRAN. We have discussed about levels of computer language.

Terminal questions

What is software and hardware?
What is computer Language?
Name the three different categories of computer languages.
What is machine language? Why is it required?
What are advantages and disadvantages of machine language?
What is assembly language? What are its advantages over machine languages?
What is the difference between source program and object program?
What is higher level languages? Why are higher level languages are easier to use.
What is compiler? Why is it required?
What is interpreter? How does it differ from compiler?

Feedback to in-text questions

In-text questions 1

1. Program is a set of instructions given to the computer by the user. Software is a set of computer programs and procedures that describe the programs. Programming is the process of software development.

2. Application Software is a set of programs to carry out operations for a specific application. System software is a set of programs written for performing tasks such as controlling all operations required to move data into and out of the computer.

3. 1. False 2. True 3. True

In-text questions 2

1. FORTRAN is used for scientific applications whereas COBOL is used for business applications.

2. Machine Languages are the only language that is directly understood by the computer. It is written in binary form that is 0 and 1. The set of symbols and letters forms the Assembly Language.

3. 1. True 2. False 3. True

In-text questions 3

1. Both compiler and interpreter are program translators used for translating higher level language into machine language. While compiler scans the entire program first and then translates it into machine code, an Interpreter translates the program line by line.

2. FORTRAN (Formula Translation) and BASIC (Beginners All-purpose Symbolic Instruction Code) are some of the high level languages.

3. 1. True 2. False 3. True

Interrupt

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is the events that makes the processor stop executing its program to perform some requested activity. There are two types of interrupts they are:

1. Hardware interrupt:
Interrupts generated by hardware devices such as keyboard, mouse, printer or chips on the system board is called hardware interrupt. Some examples of hardware interrupt are video card wants memory access, USB scanner has data, mouse moves, key pressed on keyboard, etc.

2. Software interrupt: Interrupts signals generated or caused by the programs or software are called software interrupts. Some examples: interrupt generated by the ROM BIOS during the start up for the computer, virus threat notification by the antivirus software, etc.

AI (Artificial Intelligence)

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

AI can be defined as the ability of artificial object like computer through which it will have learning, thinking, reasoning and reacting capacity as humans. AI also owes a debt to the software side of computer science, which has supplied the operating systems, programming languages, and tools needed to write modern programs.

Characteristics of AI

AI is man made and its level of activity depends on the programming capability.
It has the potential to extend problem solving ability of the system.
It has the ability to artificially simulate the human brain.
It has the ability to actively learn and adapt as a human.
It is a mechanism that is not subject to human feelings like fatigue, worry, love, etc.

Functions of Operating System

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Operating system supports the basic functions of the computer and is a low-level software. The functions of operating systems are as described below:

1. I/O management:
OS manages I/O devices and makes the I/O process effective. OS accepts the input from the input device, stores it in the main memory, ask the CPU to process it and finally provides the result to the output devices for output.

2. Command interpreter:
Command interpreter is one of the part of operating system which reads the commands that user types in at a terminal, interprets them and translate them into a detailed set of instructions that the computer hardware can understand. It varies widely from one OS to other OS. Every OS must provide command interpreter for its operation.

3. Memory management:
Memory is the large array of words or bytes, each with its own address. When user requests CPU for read/write operation, OS determines the amount of memory required for the program instructions and data. Then, OS allocates required memory to load the program and data into RAM. When program terminates its memory area is free and the same memory area is allocated for other programs.

4. Process management:
OS finds the status of processor and processes, chooses a job, chooses processer in the job, allocates the processor to the process and frees the processor when the process is executed.

5. Time sharing:
OS manages the time of CPU. The kernel OS checks frequency for other processes requesting CPU time. Time-sharing checks for CPU request from higher priority processes that are made every 10 milliseconds. When two or more processes at the same priority level are competing for the CPU time, CPU time is sliced into segments, defined by time slice and passed from process to process in a round robin fashion, preventing a single process from monopolizing the CPU until it blocks or terminates.

6. Security:
OS makes sure that only authorized users get access to the computer and its data and the users only do things they are authorized to do.

7. Deadlock prevention:
During processing, a situation can arise in which a resource shared by two or more processes cannot continue because the resource required by one process is held by the other. This situation is called deadlock. OS ensures that the above condition do not hold by carefully allocating resources.

8. Interrupt handling:
Interrupt is a signal generated from a device or program when they need attention of the CPU. OS determines the type of interrupt and priority of the interrupt, stops the execution process of CPU, preserves the initial state of the CPU, perform the requested operation and brings the CPU at the same state when it was stopped.

9. Virtual storage:
If there are programs larger than main memory (RAM) of the computer, OS uses the reserved space in the secondary memory which is termed as virtual memory. It makes the execution of larger program (than RAM) possible but at the same times the operation becomes slower.

Computer Organization

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

(Inside Computer System)

Introduction to computer organization

In the previous lesson we discussed about the evolution of computer. In this lesson we will provide you with an overview of the basic design of a computer. You will know how different parts of a computer are organized and how various operations are performed between different parts to do a specific task. As you know from the previous lesson the internal architecture of computer may differ from system to system, but the basic organization remains the same for all computer systems.

Objectives

At the end of the lesson you will be able to:

Understand basic organization of computer system
Understand the meaning of Arithmetic Logical Unit, Control Unit and Central Processing Unit
Differentiate between bit , byte and a word
Define computer memory
Differentiate between primary memory and secondary memory
Differentiate between primary storage and secondary storage units
Differentiate between input devices and output devices

Basic computer operations

A computer as shown in Fig. 2.1 performs basically five major operations or functions irrespective of their size and make. These are 1) it accepts data or instructions by way of input, 2) it stores data, 3) it can process data as required by the user, 4) it gives results in the form of output, and 5) it controls all operations inside a computer. We discuss below each of these operations.

1. Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the computer in an organized manner for processing.

2. Storage: The process of saving data and instructions permanently is known as storage. Data has to be fed into the system before the actual processing starts. It is because the processing speed of Central Processing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed. Therefore the data is first stored in the storage unit for faster access and processing. This storage unit or the primary storage of the computer system is designed to do the above functionality. It provides space for storing data and instructions.

The storage unit performs the following major functions:

All data and instructions are stored here before and after processing.
Intermediate results of processing are also stored here.

3. Processing: The task of performing operations like arithmetic and logical operations is called processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and makes all sorts of calculations based on the instructions given and the type of data provided. It is then sent back to the storage unit.

4. Output: This is the process of producing results from the data for getting useful information. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.

5. Control: The manner how instructions are executed and the above operations are performed. Controlling of all operations like input, processing and output are performed by control unit. It takes care of step by step processing of all operations in side the computer.

Functional units

In order to carry out the operations mentioned in the previous section the computer allocates the task between its various functional units. The computer system is divided into three separate units for its operation.
They are:

Arithmetic logical unit
Control unit
Central processing unit

Arithmetic logical unit (ALU)

After you enter data through the input device it is stored in the primary storage unit. The actual processing of the data and instruction are performed by Arithmetic Logical Unit. The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required. After processing the output is returned back to storage unit for further processing or getting stored.

Control unit (CU)

The next component of computer is the Control Unit, which acts like the supervisor seeing that things are done in proper fashion. The control unit determines the sequence in which computer programs and instructions are executed. Things like processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them. It also acts as a switch board operator when several users access the computer simultaneously. Thereby it coordinates the activities of computer’s peripheral equipment as they perform the input and output. Therefore it is the manager of all operations mentioned in the previous section..

Central processing unit (CPU)

The ALU and the CU of a computer system are jointly known as the central processing unit. You may call CPU as the brain of any computer system. It is just like brain that takes all major decisions, makes all sorts of calculations and directs different parts of the computer functions by activating and controlling the operations.

Fig. 2.2: Computer Architecture

Personal computer configuration

Now let us identify the physical components that make the computer work. These are:

Central Processing Unit (CPU)
Computer Memory (RAM and ROM)
Data bus
Ports
Motherboard
Hard disk
Output Devices
Input Devices

All these components are inter-connected for the personal computer to work.

In-text questions 1

1. What are the five basic operations performed by the computer?

2. Define ALU, CU and CPU.

3. Choose the correct answer:

1. The task of performing arithmetic and logical operations is called**

ALU
Editing
Storage
Output

2. The ALU and CU jointly known as

RAM
ROM
CPU
None of the above

3. The process of producing results from the data for getting useful information

Output
Input
Processing
Storage

Memory system in a computer

There are two kinds of computer memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Secondary memory such as floppy disks, magnetic disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory. Because of this the size of primary memory is less than that of secondary memory. We will discuss about secondary memory later on.

Computer memory is used to store two things: i) instructions to execute a program and ii) data. When the computer is doing any job, the data that have to be processed are stored in the primary memory. This data may come from an input device like keyboard or from a secondary storage device like a floppy disk.

As program or the set of instructions is kept in primary memory, the computer is able to follow instantly the set of instructions. For example, when you book ticket from railway reservation counter, the computer has to follow the same steps: take the request, check the availability of seats, calculate fare, wait for money to be paid, store the reservation and get the ticket printed out. The programme containing these steps is kept in memory of the computer and is followed for each request.

But inside the computer, the steps followed are quite different from what we see on the monitor or screen. In computer’s memory both programs and data are stored in the binary form. You have already been introduced with decimal number system, that is the numbers 1 to 9 and 0. The binary system has only two values 0 and 1. These are called bits. As human beings we all understand decimal system but the computer can only understand binary system. It is because a large number of integrated circuits inside the computer can be considered as switches, which can be made ON, or OFF. If a switch is ON it is considered 1 and if it is OFF it is 0. A number of switches in different states will give you a message like this: 110101….10. So the computer takes input in the form of 0 and 1 and gives output in the form 0 and 1 only. Is it not absurd if the computer gives outputs as 0’s & 1’s only? But you do not have to worry about. Every number in binary system can be converted to decimal system and vice versa; for example, 1010 meaning decimal 10. Therefore it is the computer that takes information or data in decimal form from you, convert it in to binary form, process it producing output in binary form and again convert the output to decimal form.

The primary memory as you know in the computer is in the form of IC’s (Integrated Circuits). These circuits are called Random Access Memory (RAM). Each of RAM’s locations stores one byte of information. (One byte is equal to 8 bits). A bit is an acronym for binary digit, which stands for one binary piece of information. This can be either 0 or 1. You will know more about RAM later. The Primary or internal storage section is made up of several small storage locations (ICs) called cells. Each of these cells can store a fixed number of bits called word length.

Each cell has a unique number assigned to it called the address of the cell and it is used to identify the cells. The address starts at 0 and goes up to (N-1). You should know that the memory is like a large cabinet containing as many drawers as there are addresses on memory. Each drawer contains a word and the address is written on outside of the drawer.

Capacity of primary memory

You know that each cell of memory contains one character or 1 byte of data. So the capacity is defined in terms of byte or words. Thus 64 kilobyte (KB) memory is capable of storing 64 ´ 1024 = 32,768 bytes. (1 kilobyte is 1024 bytes). A memory size ranges from few kilobytes in small systems to several thousand kilobytes in large mainframe and super computer. In your personal computer you will find memory capacity in the range of 64 KB, 4 MB, 8 MB and even 16 MB (MB = Million bytes).

The following terms related to memory of a computer are discussed below:

1. Random Access Memory (RAM): The primary storage is referred to as random access memory (RAM) because it is possible to randomly select and use any location of the memory directly store and retrieve data. It takes same time to any address of the memory as the first address. It is also called read/write memory. The storage of data and instructions inside the primary storage is temporary. It disappears from RAM as soon as the power to the computer is switched off. The memories, which loose their content on failure of power supply, are known as volatile memories .So now we can say that RAM is volatile memory.

2. Read Only Memory (ROM): There is another memory in computer, which is called Read Only Memory (ROM). Again it is the ICs inside the PC that form the ROM. The storage of program and data in the ROM is permanent. The ROM stores some standard processing programs supplied by the manufacturers to operate the personal computer. The ROM can only be read by the CPU but it cannot be changed. The basic input/output program is stored in the ROM that examines and initializes various equipment attached to the PC when the switch is made ON. The memories, which do not loose their content on failure of power supply, are known as non-volatile memories. ROM is non-volatile memory.

3. PROM: There is another type of primary memory in computer, which is called Programmable Read Only Memory (PROM). You know that it is not possible to modify or erase programs stored in ROM, but
it is possible for you to store your program in PROM chip. Once the programmes are written it cannot be changed and remain intact even if power is switched off. Therefore programs or instructions written in PROM or ROM cannot be erased or changed.

4. EPROM: This stands for Erasable Programmable Read Only Memory, which over come the problem of PROM & ROM. EPROM chip can be programmed time and again by erasing the information stored earlier in it. Information stored in EPROM exposing the chip for some time ultraviolet light and it erases chip is reprogrammed using a special programming facility. When the EPROM is in use information can only be read.

5. Cache Memory: The speed of CPU is extremely high compared to the access time of main memory. Therefore the performance of CPU decreases due to the slow speed of main memory. To decrease the mismatch in operating speed, a small memory chip is attached between CPU and Main memory whose access time is very close to the processing speed of CPU. It is called cache memory. Cache memories are accessed much faster than conventional RAM. It is used to store programs or data currently being executed or temporary data frequently used by the CPU. So each memory makes main memory to be faster and larger than it really is. It is also very expensive to have bigger size of cache memory and its size is normally kept small.

6. Registers: The CPU processes data and instructions with high speed, there is also movement of data between various units of computer. It is necessary to transfer the processed data with high speed. So the computer uses a number of special memory units called registers. They are not part of the main memory but they store data or information temporarily and pass it on as directed by the control unit.

In-text questions 2

1. Distinguish between bit and byte.

2. Define volatile and non-volatile memory.

3. Write True or False:

There are two kinds of computer memory primary and secondary.
The computer takes inputs in the form of 0 and 1.
The storage of program and data in the RAM is permanent.
PROM is secondary memory.
The memories which do not loose their content on failure of power supply are known as non-volatile memories.

Secondary storage

You are now clear that the operating speed of primary memory or main memory should be as fast as possible to cope up with the CPU speed. These high-speed storage devices are very expensive and hence the cost per bit of storage is also very high. Again the storage capacity of the main memory is also very limited. Often it is necessary to store hundreds of millions of bytes of data for the CPU to process. Therefore additional memory is required in all the computer systems. This memory is called auxiliary memory or secondary storage.

In this type of memory the cost per bit of storage is low. However, the operating speed is slower than that of the primary storage. Huge volume of data are stored here on permanent basis and transferred to the primary storage as and when required. Most widely used secondary storage devices are magnetic tapes and magnetic disk.

1. Magnetic tape: Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. In PC also you can use tapes in the form of cassettes. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and 500 meter to 1200 meter long which is coated with magnetic material. The deck is connected to the central processor and information is fed into or read from the tape through the processor. It similar to cassette tape recorder.

Advantages of magnetic tape:

Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to hold 800, 1600 or 6250 characters in each inch of its length. The maximum capacity of such tape is 180 million characters. Thus data are stored much more compactly on tape.

Economical:
The cost of storing characters is very less as compared to other storage devices.

Fast: Copying of data is easier and fast.

Long term Storage and Re-usability: Magnetic tapes can be used for long term storage and a tape can be used repeatedly with out loss of data.

2. Magnetic Disk: You might have seen the gramophone record, which is circular like a disk and coated with magnetic material. Magnetic disks used in computer are made on the same principle. It rotates with very high speed inside the computer drive. Data is stored on both the surface of the disk. Magnetic disks are most popular for direct access storage device. Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. So the reading operation is non-destructive. But if you want to write a new data, then the existing data is erased from the disk and new data is recorded.

3. Floppy Disk: It is similar to magnetic disk discussed above. They are 5.25 inch or 3.5 inch in diameter. They come in single or double density and recorded on one or both surface of the diskette. The capacity of a 5.25-inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes. It is cheaper than any other storage devices and is portable. The floppy is a low cost device particularly suitable for personal computer system.

4. Optical Disk:

With every new application and software there is greater demand for memory capacity. It is the necessity to store large volume of data that has led to the development of optical disk storage medium. Optical disks can be divided into the following categories:

Compact disk/ read only memory (CD-ROM): CD-ROM disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. Here the storage density is very high, storage cost is very low and access time is relatively fast. Each disk is approximately 4 1/2 inches in diameter and can hold over 600 MB of data. As the CD-ROM can be read only we cannot write or make changes into the data contained in it.

Write once, read many (WORM): The inconvenience that we can not write any thing in to a CD-ROM is avoided in WORM. A WORM allows the user to write data permanently on to the disk. Once the data is written it can never be erased without physically damaging the disk. Here data can be recorded from keyboard, video scanner, OCR equipment and other devices. The advantage of WORM is that it can store vast amount of data amounting to gigabytes (109 bytes). Any document in a WORM can be accessed very fast, say less than 30 seconds.

Erasable optical disk: These are optical disks where data can be written, erased and re-written. This also applies a laser beam to write and re-write the data. These disks may be used as alternatives to traditional disks. Erasable optical disks are based on a technology known as magnetic optical(MO). To write a data bit on to the erasable optical disk the MO drive’s laser beam heats a tiny, precisely defined point on the disk’s surface and magnetizes it.

Input output device

A computer is only useful when it is able to communicate with the external environment. When you work with the computer you feed your data and instructions through some devices to the computer. These devices are called Input devices. Similarly computer after processing, gives output through other devices called output devices.

For a particular application one form of device is more desirable compared to others. We will discuss various types of I/O devices that are used for different types of applications. They are also known as peripheral devices because they surround the CPU and make a communication between computer and the outer world.

Input devices

Input devices are necessary to convert our information or data in to a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing followings are the most useful input devices.

1. Keyboard: – This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter of the type QWERTY. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys. A typical keyboard used in a computer is shown in Fig. 2.6. You have to press correct combination of keys to input data. The computer can recognize the electrical signals corresponding to the correct key combination and processing is done accordingly.

Fig. 2.6

2. Mouse: – Mouse is an input device that is used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface the screen censors the mouse in the direction of mouse movement. The cursor moves very fast with mouse giving you more freedom to work in any direction. It is easier and faster to move through a mouse.

3. Scanner: The keyboard can input only text through keys provided in it. If we want to input a picture the keyboard cannot do that. Scanner is an optical device that can input any graphical matter and display it back. The common optical scanner devices are Magnetic Ink Character Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).

Magnetic ink character recognition (MICR): This is widely used by banks to process large volumes of cheques and drafts. Cheques are put inside the MICR. As they enter the reading unit the cheques pass through the magnetic field which causes the read head to recognise the character of the cheques.

Optical mark reader (OMR): This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil. These answer sheets are directly fed to a computer for grading where OMR is used.

Optical character recognition (OCR): This technique unites the direct reading of any printed character. Suppose you have a set of hand written characters on a piece of paper. You put it inside the scanner of the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a character read. Patterns that cannot be identified are rejected. OCRs are expensive though better the MICR.

Output devices

1. Visual display unit: The most popular input/output device is the Visual Display Unit (VDU). It is also called the monitor. A Keyboard is used to input data and Monitor is used to display the input data and to receive massages from the computer. A monitor has its own box which is separated from the main computer system and is connected to the computer by cable. In some systems it is compact with the system unit. It can be coloror monochrome.

2. Terminals: It is a very popular interactive input-output unit. It can be divided into two types: hard copy terminals and soft copy terminals. A hard copy terminal provides a printout on paper whereas soft copy terminals provide visual copy on monitor. A terminal when connected to a CPU sends instructions directly to the computer. Terminals are also classified as dumb terminals or intelligent terminals depending upon the work situation.

3. Printer: It is an important output device which can be used to get a printed copy of the processed text or result on paper. There are different types of printers that are designed for different types of applications. Depending on their speed and approach of printing, printers are classified as impact and non-impact printers. Impact printers use the familiar typewriter approach of hammering a typeface against the paper and inked
ribbon. Dot-matrix printers are of this type. Non-impact printers do not hit or impact a ribbon to print. They use electro-static chemicals and ink-jet technologies. Laser printers and Ink-jet printers are of this type. This type of printers can produce color printing and elaborate graphics.

In-text questions 3

1. Distinguish between impact and non-impact printers.

2. Define soft copy and hard copy terminals.

3. Write True or False:

Secondary memory is called Auxiliary memory.
The magnetic tapes and magnetic disk are primary memories.
A CD-ROM is read only memory.
Mouse is an output device.
Printer is an important output device.

What you have learnt

In this lesson we discussed five basic operations that a computer performs. These are input, storage, processing, output and control. A computer accepts data as input, stores it, processes it as the user requires and provides the output in a desired format. The storage unit of a computer is divided into two parts: primary storage and secondary storage. We have discussed the devices used for these two types of storage and their usefulness.

Terminal questions

What are the five basic operations performed by any computer system?
Draw a block diagram to illustrate the basic organization of computer system and explain the function of various units.
What is input device? How does it differ from output device?
Differentiate between RAM and ROM. Also distinguish between PROM and EPROM.
What is cache memory? How is it different from primary memory?
Write short notes on:

Control Unit
Random Access Memory (RAM)

Feedback to in-take questions

In-text questions 1

1. The five basic operations that a computer performs are input, storage, processing, output and control.

ALU: Arithmetic Logic Unit
CU: Control Unit
CPU: Central Processing Unit

3. 1,3,1

In-take questions 2

1. A bit is an acronym for binary digit, which stands for one binary piece of information. This can be either 0 or 1. A byte is equal to 8 bits.

2. The memories which are erased if there is a power failure are known as volatile memories. RAM is an example of volatile memory. The memories, which do not loose their content on failure of power supply, are known as non-volatile memories. ROM is non-volatile memory.

3. 1. T 2. T 3. F 4. F 5. T

In-take questions 3

1. Impact printers use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon. Non-impact printers do not hit or impact a ribbon to print. They use electro-static chemicals and ink-jet technologies.

2. A hard copy terminal provides a printout on paper whereas soft copy terminals provide visual copy on monitor.

3. 1. T 2. F 3. T 4. F 5. T

Communication Port

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is a hardware device used for connecting peripherals devices with the computer. It has major functions like:

Connecting peripheral devices.
Transmitting data to and fro from peripheral devices.
Providing electrical power to the small peripheral devices.

Some of the communication ports used are:

- Serial port
It is used for connecting slow speed devices like keyboard, mouse, etc. It also provides electrical power supply to these devices. It cam transmit 1 bit data at a time.

- Parallel port
It is used for connecting medium speed devices like monitor, printer, etc. It can transmit 8 bit data at a time.

- USB (Universal serial bus)
USB is the common interface developed by multiple hardware developers for supporting large variables of devices. It is used to connect keyboard, monitor, pen drive, etc. It is the most common user interface at present.

- SCSI
It is used for connecting external memory devices like magnetic tape, multiple hard disk, etc.

- IEEE 1394 interface
This interface is used for connecting high speed devices like connecting audio/video equipments, aeronautical devices, medical equipments, etc.

- PCI (Peripheral communications interface)
It is used for connecting peripheral devices like internal modem, internal TV card, sound card, graphics card, etc with the computer. It is available in the mother board.

Email Service

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Email service is used for transmitting electronic or soft-copy documents, message by using electronic devices like computer, computer network, internet, etc. present e-mail service is based on stored and forward concept i.e. email sent by the sender is stored in email server before forwarding it to the receiver. It doesn’t require the sender and receiver to be connected at the same time. Traditionally, the older concept of email required both sender and receiver to be connected at the same time.
It uses protocols like SMTP, POP, IMAP, etc.

Features of e-mail:

It is faster and cheaper medium of communication.
It is reliable.
It is secured communication.
It can be used for transmitting text, image, audio, video.
Same message can be sent to multiple users at the same time by using CC (Carbon Copy) and BCC (Blind Carbon Copy).
It may or may not use internet directly.

Types:

Web based email
POP email service

1. Web based email:
It is the internet based mailing system. It requires internet connection and a browser to send or receive the message. Email providers like hotmail.com, yahoo.com, gmail.com, etc. provide internet based email. It is the most widely used email service.

2. POP email service:
This email service is provided by local email or network providers. It requires connection to the e-mail provider and email client software like:

Outlook express
Thunderbird
Eudora
Kmail, etc.

It can be used from the system with email client software and proper setting to connect email providers.

Types of OS

Computer 11 Notes — Sun, 08 Apr 2012 05:41:42 +0000

1. On the basis of processing

Batch Processing OS
Multitasking OS
Multiprocessing OS
Multiprogramming OS
Real-time OS
Multithreading OS

2. On the basis of user interface

3. On the basis of mode of user

Single user OS
Multiuser OS

Batch processing

A batch processing is a group processing system in which all the required inputs of all the processing task are provided initially. The result of all the task are provided after the completion of all the processing. Its main features are

Multiple task are processed.
User cannot provide input in between processing.
It is appropriate only when all the inputs are known in advance.
It requires larger memory.
CPU idle time is less.
Printer is the appropriate output device.
It is old processing technique and rarely used at present.

Multitasking OS are of two types:

Pre – empetive multitasking
Co-operative multitasking

In the pre-empetive multitasking, the OS allows CPU time slices to each program. After each time slice, CPU executes another task.

Example:- Windows XP

In co-operative multitasking, a task can control CPU as long as it requires. However , it will free CPU to execute another progrqam if it doesn’t require CPU

Example :- Windows 3x , Multifinder

Multiprocessing OS

A multiprocessing OS can support the execution of multiple number of the same time. It uses multiple number of CPU. It is costlier. However, the processing speed will be faster. It is complex in its execution.

Operating system like Unix,64bit edition of windows, server edition of windows, etc are multiprocessing.

Multiprogamming OS

In a multiprogramming OS, more than one programs can be used at a same time. It may or may not be multiprocessing, In a single CPU system, multiple programs are executed one after another by dividing the CPU in small time slices.

Example :- Windows, linux, Unix, etc.

Multithreading OS

A program in execution is known as process. A process can be further divided into multiple sub processes. These sub- processes are known as threads. A multi-threading OS can divide process into threads and execute those threads. This increases operating speed but also increases the complexity.

Example :- Unix, Server edition of Linux and Windows