Computer Science Notes For Class 9 ( Introduction to Computer)

Chapter No. 1: Introduction to Computer

Q. What is computer?

Ans.: Computer:-The word computer is derived from a word “Compute” which means “to calculate”. Computer may be defined as:
“A computer is an electronic data processing machine that accepts data and instructions (programs) as input, processes the data according to given instructions and produces information as output.”
Computer can also be defined as:
“A computer is an electronic data processing machine, which works under control of stored programs, accepts the data, processes the data according to instructions (programs) and gives information (result).”

Q. Write down capabilities of computer. 
Ans. Capabilities of Computer:-The capabilities of computer are given below:
1. Speed:-A computer can process the data faster than any other machine.
2. Repetitions:-A computer can perform the same operations millions of times in exactly the same way without getting bored or feeling tiredness.
3. Accuracy:-A computer processes the data with high-accuracy.
4. Logical Operations:-The computer can make decisions if it is provided some conditions and their alternatives.
5. Store and Recall Information:-Computer has memory and storage devices where data, programs and information are stored and recalled back.
6. Self-Checking:-The computer verifies the accuracy of its own work by means of a parity check.

7. Self-Operating:-Computer can execute the instruction on its own without human intervention, if the data and programs are fed into computer memory.
Q. Write down limitations of computer.
Ans. Limitations of Computer:-Though a computer is a very efficient device but there are some limitations of this device. Some of them are given below:
· A computer cannot generate information on its own.
· A computer cannot correct instructions if they have mistaken.
· A computer cannot come with an original decision.

Q. Write a short note on Data processing cycle?

Ans: Data processing cycle:

1) Input   2) Processing 3) Output

1) Input: In this step data or information is fed to a computer system with the help of input devices.

2) Processing: In this step inputted information is fed to the C.P.U for processing.

3) Output: In final step of data processing, the results of processing step are transferred to output devices.

Q. What is firmware and liveware?

Ans: Firmware: Software  (programs or data) that has been written onto read-only memory (ROM). Firmware is a combination of software and hardware.

Liveware :People who work with computers, as opposed to the software or hardware they use; loosely, human beings, as opposed to technology. 

Q. What is the difference between hardware and software?

Ans. DIFFERENCES BETWEEN HARDWARE AND SOFTWARE:

HARDWARE	SOFTWARE
Definition
Hardware is the collection of all the parts you can physically touch and feel. They are the physical components of computer system and interconnection.	Software is a collection of programs/instructions used to operate computers and related devices. A general name given to all programs which make computer useful.
Examples
CD-ROM, monitor, printer, video card, scanners , label makers, routers , and  etc.	Internet Explorer , Microsoft Word , Microsoft Excel, windows , antivirus , virus browsers & etc.
Types
Input, storage, processing, control, and output devices.	System software, Programming software, and Application software.
Nature
Hardware is physical in nature.		Software is logical in nature.

Q. What is an Abacus?

Ans. History: Abacus is one of the earliest and simplest computing devices. It was developed around 3000 BC.

Abacus: An abacus is a rectangular wooden frame carrying several parallel wires. Each wire supports a number of beads which are free to slide along the wires.

Purpose and Function of Abacus:

Abacus was used for addition or counting. For the addition of two numbers, first number is dialed by moving the beads down. Then second number is dialed by moving a specific number of beads down. The total number of beads below represents the sum of two numbers.

Q. Describe different earliest computing devices?

OR

Write a note on:

 (i) Napier’s Bones  (ii) Slide Rule  (iii) Pascaline  (IV) Difference Engine

(v) Analytical Engine

Ans. Mechanical Computing Devices:

I) Napier’s bones: In 1614, John Napier invented logarithms and a device called Napier‟s bones or rods. The rods helped to multiply numbers. These rods were fast and accurate.

II) Slide Rule: A slide rule consists of two scales; the „rule‟, „slide‟ and a transparent rectangular moving piece called cursor.

III) Pascaline: In 1642, a 19 years old boy Blaise Pascal developed a machine that could add and subtract. It consisted of a series of wheel or dials. Each dial had 10 digits from 0 to 9 on it. These dials were geared with drums. These drums also had digits from 0 to 9 which were displayed through windows.

IV) Difference Engine: In 1786 J. H. Muller proposed a calculating machine called a „difference engine‟. The idea was conceived by Charles Babbage but he could not complete it after 10 years of labor. At the end Charles Babbage stopped working on the „difference engine‟.

V) Analytical Engine: After failing to develop „difference engine

‟, Charles Babbage started developing a new machine called „analytical engine‟. It could be programmed to evaluate a wide range of arithmetical expressions. Analytical Engine consisted of five units:-

1) Store: This part was used to store the numbers entered into the machine and those which had to be generated at the time of processing.

2) Mill: This was the processing unit which performed all the calculations (arithmetic operations) by moving gears.

3) Control: Control Unit was used to control all other units. It was used to transfer the numbers to and from the mill.

4) Input: Input Unit was used to feed numbers in the „analytical engine‟. Input media was punched cards.

5) Output: Output Unit was used to display the results of calculations.

Q. Draw a generation table?

Generation	Duration	Electronic Components	Cost	Size	Language	Peripheral Devices	Processing Speed
First	1940-56	Vacuum tubes	Very expensive and special purpose	Very large like room	Machine language	Punched cards & output on paper, no secondary storage	Slow speed with very small memory
Second	1956-63	transistors	Still Very expensive and special purpose	large	Assembly language, COBOL ,Fortan	Bubble memory	fast speed with very large memory
Third	1964-71	Integrated circuits(ICs)	expensive but special purpose	Comparatively small but desktop were introduced	Basic, C, Pascal,	Keyboard , monitors , magnetic disk with operating system	Very fast speed with very larger memory
Fourth	1971-Present	microprocessor	Less expensive and general purpose	Very small and highly portable like laptops	More versatile high level languages	Mouse handheld devices with  GU , Usb, cd	Fastest among all with huge memory
Fifth	Present-beyond	Artificial intelligence	Work in progress	Work in progress	Natural language	Voice recognition	Parallel processing

Q. What are generations of computer? Explain

Ans. Generations of computers

1.First Generation of Computers (1940-1956)

2.Second Generation Computers (1956-1963)

3.Third Generation Computers (1964-1971)

4.Fourth Generation Computers (1971-Present)

5.Fifth Generation Computers (Present-beyond)

1. First Generation of Computers

Vacuum tubes were used in the computers of First Generation. The first generation computers had the following

Characteristics:

i. Very big in size

ii. Slow in speed

iii. Low reliability

iv. Large power consumption

v. Difficult maintenance

 Advantages

›  Vacuum tubes were the only electronic component available during those days.

›  Vacuum tube technology made possible to make electronic digital computers.

›  These computers could calculate data in millisecond.

Disadvantages

›  They were not very reliable.

›  Air conditioning was required.

›  Very slow speed.

Examples of First Generation Computers: UNIVAC(Universal Automatic computer), EDSAC, EDVAC

2. Second Generation of Computers

Transistors were used in the computers of Second Generation. Transistors were smaller, reliable as compared to Vacuum Tubes. They consumed less power. Second Generation computers were able to perform a single operation in microseconds and were capable to store huge data. Second Generation computers had the following

 Characteristics:-

i. Extremely reliable as compared to the First Generation computers.

ii. Compact in size.

iii. Less power consumption.

iv. Use of card readers, magnetic tapes, magnetic discs, printers etc.

v. Use of computer languages.

Advantages

›  Accuracy improved.

›  The 2nd generation Computers were more reliable

›  Used less energy and were not heated.

›  Wider commercial use

Disadvantages

›  Cooling system was required

›  Constant maintenance was required

›  Commercial production was difficult

›  Only used for specific purposes

›  Costly and not versatile

›  Punch cards were used for input.

Example of Second Generation Computers: IBM-704

3. Third Generation of Computers

Integrated Circuits (ICs) were used in the computers of Third Generation. An IC chip contains many circuits such as transistors, diodes and resistors interconnected with one another. Mini computers were developed in Third Generation.

Third Generation computers had the following

Characteristics:-

i. Very small size as compared to the second generation

ii. Consumed very little power

iii. More reliable

iv. Less costly as compared to previous generations

v. Use of real-time programming

vi. Use of multiprogramming

vii. Use of Data Base Management Software

viii. Large storage capacity

Advantages

›  Used faster peripherals like tape drives, magnetic disks, printer etc.

›  Used Assembly language instead of Machine language.

›  Accuracy improved.

Disadvantages

›  Air conditioning was required.

›  Highly sophisticated technology required for the manufacturing of IC chips.

Examples of Third Generation Computers: IMB-85, System-360 series etc.

4. Fourth Generation of Computers

Microprocessors (1971) were firstly used in Fourth Generation computers. They contained VLSI (Very Large Scale Integration) circuits. A VLSI contained a complete Central Processing Unit (CPU) on a single semiconductor chip. Fourth Generation computers had the following characteristics:-

i. Very efficient and fast

ii. Very Large storage

iii. Very little power consumption

iv. Very Cheap as compared to the computers of 1st, 2nd and 3rd generation computers.

v. Use of Microprocessor

vi. Use of T.V. screens now called monitors

vii. Could perform arithmetical and logical operations

›  Advantages

›  More powerful and reliable than previous generations.

›  Small in size

›  Fast processing power with less power consumption

›  Fan for heat discharging and thus to keep cold.

›  No air conditioning required.

›  Totally general purpose

›  Commercial production

›  Less need of repair.

›  Cheapest among all generations

›  All types of High level languages can be used in this type of computers

Disadvantages

›  The latest technology is required for manufacturing of Microprocessors.

›  Very advance technology was required to make the ICs.

›  Air conditioning was required in many cases due to ICs.

Examples of Fourth Generation Computers: ZX80, ZX81, Apple series etc.

5. Fifth Generation of Computers

Artificial Intelligence (AI) and Expert Systems are the technologies of Fifth Generation of computers. There was very little hardware change in Fifth Generation computers but a revolution in software. Following are the characteristics of Fifth Generation computers:-

i. Artificial Intelligence

ii. Expert Systems

iii. Large thinking power as compared to previous generations.

iv. Increased speed

v. Increased efficiency

vi. Reduced size

vii. Reduced cost

Advantages

›  It is more reliable and works faster.

›  Available in different sizes with unique features

Disadvantages

›  Not discovered yet.

Q. How computers are classified? Explain.

Ans. Classification of Computers:

  By Purpose

A.    General purpose computers

B.      Special purpose computers

By Function

A.    Analog computer

B.     Digital computers

C.     Hybrid computers

By Size

A.    Mainframe computer

B.     Super computer

C.     Mini computer

D.    Micro computer

Q. What are different types of computers according to their puposes? Explain.

Ans. Types of Computers (according to their purposes)

A.    General purpose computers

B.      Special purpose computers

General Purpose computers:

Ø  General Purpose computers are those that allow users to do various tasks. 

Ø  And not a specific task. 

Ø  Examples: personal computers - it helps us to do things like playing games, chatting, organizing, authoring, internet browsing etc. 

Special purpose computers

Ø  Special purpose computers are those that are made to do special tasks.

Ø  And mostly its does only one task (task related to that particular field) 

Ø  Examples: IBM Deep Blue which is a supercomputer that's made for just playing chess. And nothing other than that. So it’s a special purpose computer.

Q. What are different types of computers according to their working? Explain.

Ans. Types of Computers (according to their working)

There are three types of computers according to their working and design:-

1. Analog Computers

2. Digital Computers

3. Hybrid Computers

1. Analog Computers:

Ø  An analog computer accepts data in continuous or physical form and represents it in a suitable form to perform scientific operations.

Ø  It processes analog data e.g. speed, pressure, temperature, fluid flow, voltage, current etc.

Ø  Analog Computers are Special Purpose Computers. They are very fast.

Ø  Examples of Analog Computers: Speedometer, thermometer etc.

2. Digital Computers:

Ø  An analog computer accepts data in form of digits and represents it in the form of discrete numbers.

Ø  It processes digital data and performs arithmetic and logic operations.

Ø  Digital Computers are General Purpose Computers.

Ø  They are accurate as compared to Analog Computers. Computers at our schools, homes and offices are digital computers.

Ø  Examples of Digital Computers: PCs or computers at our homes.

3. Hybrid Computers:

Ø  Hybrid Computers are combination of features of digital and analog computers.

Ø  They are Special Purpose Computers which are fast and accurate.

Ø  Examples of Digital Computers: Computers at Hospitals in ICUs, telemetry, spaceships, guided missiles etc.

Q. What are different types of computers according to their sizes? Explain.

Ans. Types of Computers (according to their sizes)

There are four types of computers according to their sizes

1. Super Computers:

Ø  Super Computers are the largest and the fastest computers which can perform hundreds of millions of instructions per second.

Ø  First Super Computer was developed in 1980s.

Ø  Examples of Super Computers: CRAY-1, CRAY-2, CYBER 205 etc.

Fields in which Super Computers are used: Space Exploration, Weather forecasting, Aircraft Design, Nuclear Research etc.

Ø  Characteristics of Super Computer:

i. Extraordinary computing power.

ii. Special Purpose Computers.

iii. Very Expensive

iv. Used by very large organizations.

2. Mainframe Computers:

“A large digital computer serving 100-400 users and occupying a special air-conditioned room is called a mainframe computer.”

Ø  Mainframes are large-scale computers.

Ø  These computers need very large rooms and other arrangements like cooling etc.

Ø  Mainframes are very fast and have very large memory.

Ø  They support many users and can do different jobs for different users. In short:

Ø  Examples of Mainframe Computers: IBM-4341, CYBER 176 etc.

Ø  Fields in which Mainframe Computers are used: Banks, Airlines, Universities etc.

Characteristics of Mainframe Computer.

A.        Large Scale Computers

B.        Very fast

C.        Very Large Memory

D.        Support 100-400 users simultaneously

E.         Multiple Processing Computers

3. Mini Computers: “A mid-sized computer, usually fitting within a single cabinet about the size of a refrigerator, that has less memory than a mainframe is called a Mini Computer.”

Or

“Computer that possesses the same components as large mainframes but has reduced memory and slower processing speeds is called a Mini Computer”.

Ø  Mini Computers can support multiple-users and multiple tasks like mainframes through the use of terminals.

Ø  They were firstly used in 1960s. In short:

Ø  Example of Mini Computers: PDP-1

Ø  Fields in which Mini Computers are used:

Large Businesses, Education and Government sector etc.

Characteristics of Mini Computer:

i. Mini Computers can handle larger amount of data than microcomputers

ii. They perform the functions of a mainframe computer with slightly slower speed.

iii. They support multiple users

iv. These computers are Multiple Processing Computers.

4. Micro Computers:

“A small digital computer based on a microprocessor (VLSI Circuit) and designed to be used by one person at a time is called a microcomputer.”

Ø  A Micro Computer is a relatively inexpensive computer that is rapidly being used in all application areas. In short:

Ø  Example of Micro Computers: IBM PC, AT&T etc.

Ø  Fields in which Micro Computers are used:

Large Businesses, Education and Government sector etc.

Characteristics of Micro Computers:

i. Microcomputers are inexpensive computers.

ii. Microcomputers are smaller in size.

iii. Microcomputers are very powerful but less powerful than super, mini or mainframe computers.

iv. Microcomputers are General Purpose Computers.

Q. What is the impact of computers on society? Also explain the use of computers in different fields of life.

Ans. Impact of Computers on Society:

Computer is known as the most popular and wonderful discovery of the 21st century. It has influenced the society heavily. It is seen everywhere and everybody wants to get use of it. It is seen at houses, offices, school, colleges, universities, banks and hospitals. Computers are being used as typewriters, calculators, VCRs, TVs, telephones and communicational tools.

Applications of Computers: Computer has applications in the following fields of life.

Applications in Education

Computers improve both teaching and student achievement. The present generation students like to embrace all the things in the ambit of this modern technology. The educators are feeling shy and reluctant to accept technology as their work partner.

Applications in Medical Field

A patients prescribed medications (past and present) can also be stored in a computer system in a hospital. This makes it much easier to transfer any prescriptions and data that a patient needs to local or national drug stores or hospitals. Past hospital visits and billing information can be stored and kept for further use or future hospital experience. For example, doctors keep a computer handy anytime they prescribe a medication

Applications in Science

The advent of computers has contributed greatly to the fields of science. They have allowed for the collection and recording of vast amounts of data. They allow scientists to store information indefinitely and review it easily.
Applications in Business:

Computers are being used by all businesses. Some of computer uses in business are as under:-

To record stocks

To make customer bills

To analyze sales

To calculate employee’s pay

Applications in Banking:

Banks are the largest users of computer. Some of computer uses in banking are as under:-

To record day to day processing of customer’s account

To facilitate customers in using their credit cards for purchasing a product

To make automatic debit form

To update customer’s accounts

Applications in Product Design and Manufacturing:

Manufacturing companies use computers from the design stage to the manufacturing stage. Computer Aided Design (CAD)  software help to develop a representation of the product and help testing it in a variety of simulated environments.

Q. What is a program?What is a programming language?

Ans. Program:

“An organized list of instructions that, when executed, causes the computer to behave in a predetermined manner”.

*Without programs computers are useless

Programming Languages:

Ø  When a user wants to communicate to the computer, he needs to give the computer a set of instructions. This is done with the help of a programming language.

Ø  Programming is a way to communicate with computer.

Ø  Computer understands binary number system only consisting of digits 0 and 1. A group of binary digits is called a code.

Q. What is the difference between a High Level Language and a Low Level Language?

Ans:There are two major categories of languages:

High level language	low level language
Learning
High-level languages are easy to learn.	Low-level languages are difficult to learn.
Understanding
High level languages are near to human languages	Low-level languages are far from human languages
Execution
Programs in high-level languages are slow in execution.	Programs in low-level languages are fast in execution
Uses
These languages are normally used to write application programs.	These languages are normally used to write hardware programs
Modification
Programs in high-level languages are easy to modify.		Programs in low-level languages are difficult to modify

Q. What are Low Level Languages? What is the difference between machine language and assembly language?

Ans. Low Level Languages:

Ø  Low Level Languages are those languages which are hard to understand for man.

Ø  They are not like English or natural languages.

Ø  They are closer to the computer and a computer directly understands them.

Ø  These languages are more powerful and user is independent to develop whatever he wants to.

Ø  There are two Low Level Languages; Machine Language and Assembly Language:

Machine Language:

Ø  A set of binary instruction codes which a computer directly understands is called Machine Language.

Ø  It is a Low Level Language.

Ø  It differs from computer to computer.

Ø  It is also called „language of the processor‟ or „mother language of computer‟.

Ø  It is hard to understand by user as it is in the form of binary digits.

Assembly Language:

Ø  Assembly Language is also a low level language but it uses short symbolic phrases understandable by user / programmer.

Ø  These alphanumeric symbols are called mnemonic codes.

Ø  Assembly Language is not directly understandable by the computer. So, each program of Assembly Language is assembled into Machine Language with the help of an assembler.

Ø  An assembler is a program which converts Assembly Language program into Machine Language.

Q. What are the advantages of Assembly Language over Machine Language?

Ans. Advantages of Assembly Language:

Easier than Machine Language

Easier to debug

Easier to modify

Q. Briefly describe the following languages.

i. BASIC ii. FORTAN

iii. COBOL iv. PASCAL

v. ADA vi. C

vii. C++

Ans. Description of Different High Level Languages

i. BASIC: BASIC (Beginner’s All-purpose Symbolic Instruction Code) was developed in 1964. It is close to English. A person with little programming knowledge can It is:

Easy to Understand

Easy to write programs

Easy to locate and debug errors

ii. FORTAN (Formula Translations): FORTRAN was developed in 1964 for IBM computers. Its latest version is FORTRAN 90.

iii. COBOL (Common Business Oriented Language): COBOL was developed in 1959. It was developed for general, commercial and business purpose. It was used handle large amount of data.

iv. PASCAL: Pascal was developed during the early 1970‟s. Pascal is also a HLL named after the French mathematician and scientist Blaise Pascal. It is a general purpose language.

v. ADA: ADA was developed in 1980. It was named after the first programmer Augusta Ada Byron. It is a High Level structured programming language which was used in military applications.

vi. C Language: C language was developed in 1974 by Brian Karnighan and Dennis Ritchie. It is used for developing Operating Systems. C is extremely powerful High Level Language.

vii. C++: C++ was developed in the early 1980s by Bjarne Stroustrup. It is the most powerful High Level Language. It is like C but supports Object Oriented Programming.

Q. What are language Translators? Explain each of them.

Ans Language Translators:

A language processor is translating software which translates the High Level Language or Assembly Language program into machine language.

There are three types of translators or language processors:-

1. Compiler:

A compiler is translating software which converts the High Level Language programs into machine language. It converts the whole program at once.

2. Interpreter:

An interpreter is translating software which converts the High Level Language programs into machine language line-by-line.

3. Assembler: An assembler is also system software which assembles / converts assembly language programs into machine language.

Q. Differentiate between compiler and interpreter?

Compiler	Interpreter
A compiler is translating software which converts the High Level Language programs into machine language	An interpreter is translating software which converts the High Level Language programs into machine language
It converts the whole program at once.	It converts the program line-by-line.
Compiler generates the error report after the translation of the entire page.	Interpreter will stop the translation after it gets the first error.

Q. Why do we need a language Translators? OR why the source code is needed to be translated into machine code?

Ans.  Basically source code can be converted   to machine code (0,1s) using language translator. we need language translator in a system software because computer can’t understand our language .Therefore translator converts high level language into low level language & vice versa as computer can only understand in binary format.

 Low level language handles entire hardware and instructions set architecture of a computer directly. Language translator software converts high level language into low level language.