Introduction to computer

1. Elaborate the following: MIPS, OMR, ROM, WWW, USB, MBR, FAT, GUI, POP, RPM, LCD, SFTP, RAM, EPROM, DVD, MAN, CRT, URL, FTP, LAN, WAN, ENIAC, EDVAC, EDSAC, UNIVAC, ABC, IBM, PC, CD, CPS, BCD, EBCDIC, ASCII, CPU, ALU, HDD, FDD, EPROM, EEPROM, RAM, CGA, VGA, SVGA, AGP, CCD, OSI, ISO, NIC, LASER, LED, TCP/IP, NOS, HTML, HTTP, SMTP, IRC, NNTP.

Ans. to the question no: 1

MIPS - Millions Instructions Per Second

OMR – Optical Mark Reader

ROM – Read Only Memory

WWW – World Wide Web

USB – Universal Serial Bus

MBR – Master Boot Record

FAT – File Allocation Table

GUI – Graphical User Interface

POP – Post Office Protocol

RPM – Revolutions Per Minute

LCD – Liquid Crystal Display

SFTP – Secure File Transfer Protocol

RAM – Random Access Memory

EPROM – Erasable Programmable Read Only Memory

DVD – Digital Video Disc

MAN – Metropolitan Area Network

CRT – Cathode Ray Tube

URL – Uniform Resource Locator

FTP – File Transfer Protocol

LAN – Local Area Network

WAN – Wide Area Network

ENIAC – Electronic Numerical Integrator And Calculator

EDVAC – Electronic Discrete Variable Automatic Computer

EDSAC – Electronic Delay Storage Automatic Computer

UNIVAC – Universal Automatic Computer

ABC – Atanasoff Berry Computer

IBM – International Business Machine

PC – Personal Computer

CD – Compact Disk

CPS – Characters Per Second

BCD – Binary Coded Decimal

EBCDIC – Extended Binary Coded Decimal Information Code

ASCII – American Standard Code of Information Interchange

CPU – Central Processing Unit

ALU – Arithmetic Logic Unit

HDD – Hard Disk Drive

FDD – Floppy Disk Drive

EPROM – Erasable Programmable Read Only Memory

EEPROM – Electrically Erasable Programmable Read Only Memory

RAM – Random Access Memory

CGA – Color Graphics Adapter

VGA – Virtual Graphics Array

SVGA – Super Virtual Graphics Array

AGP – Accelerated Graphics Port

CCD – Charge Coupled Devices

OSI – Open Systems Interconnection

ISO – International Standards Organization

NIC – Network Interface Card

LASER – Light Amplification by Stimulated Emission of Radiation

LED – Light Emitting Diode

TCP/IP – Transmission Control Protocol/Internet Protocol

NOS – Network Operating Systems

HTML – Hypertext Markup Language

HTTP – Hypertext Transfer Protocol

SMTP – Simple Mail Transfer Protocol

IRC – Internet Relay Chat

NNTP - Network News Transfer Protocol

—— ○ ——

2. What are the features that distinguish computers from other machines?

Ans. to the question no: 2

Computers can be programmed. Programming means that a computer can be instructed in detail about what it should do in solving a problem.   This unique feature enables computer to have diverse use and endless possibility.

Ø  Speed: Computers work lot faster than human, especially in numerical calculations. Two mod­erately long integer numbers can be added in a very small fraction of second that may need few minutes for human. Computer speeds are measured in MIPS (Millions Instructions per Second). Five to six years ago, a typical desktop computer had speed of around five MIPS whereas, now computers with speed of less than forty MIPS are hard to find.

Ø  Accuracy: Computers function accurately because their-principles are based on mathematical laws. If the data provided by the users are good, and the program used to process them is flawless, then a computer is expected to produce the same accurate result every time it runs. However, compute human programmers who are prone to make mistakes that end up in generating wrong results develop programs.

Ø  Diligence: Computers neither get tired after long use nor get bored for repetitive use the only boredom is the heat produced by the different components inside. If enough measures are taken to remove that extra heat, computers can function continuously for their entire life.

Ø  Price Decline: This is an unusual feature of computers and related accessories. Where prices of most things rise with time, computer prices tend to decline. Added to that, they come with faster speed and extra features. The factors contributing this price decline are the extraordinary development in semiconductor technology, improvement in manufacturing engineering and higher sales. Some people argue that, with the price decline, the reliability of computers has been compromised.

Ø  Automation: Computers can work automatically. If the required data and instructions are provided, computers can process them without requiring any intervention of human operator. The results produced can be instructed to store in proper place. Most of the modern manufacturing plants are now computer controlled. A TV advertisement can be a good example.

Ø  Memory: Computers have been designed with the ability to store. Data and instructions given to a computer system are usually stored in temporary memory for immediate processing. For future use, they are stored in permanent storage. Computer memories do not get erased or weak after multiple times of use.

—— ○ ——

3. Write short notes on different types of computer.

Ans. to the question no: 3

Supercomputers: The large and powerful mainframe computer is called a supercomputer. The supercomputer is the top of the heap in power and expense.

Figure 3.1: Cray XMP Supercomputer.

1. Largest and fastest
2. Several million dollars
3. Can process enormous volume of data
4. Over 50 BIPS (Billions Instructions Per Second)
5. Uses

Ø  Weather forecasting

Ø  Code breaking

Ø  Special effects

Ø  Engineering design

Ø  Economic forecasting

Ø  Space research and administration

Ø  Researches for Genetic Engineering and DNA mapping.

Ø  Astronomical and Cosmological researches

Ø  Calculating the value of pi (π)

Example: Cray-11, Cray-XMP, Cray-T90 and Cyber-250.

Main Frame: The main frame is the workhorse of the business world. A main frame is the heart of a network of computers or terminals, which allows hundreds of people to work at the same time on the same data. It requires a special environment, cold and dry.

Figure 3.2: IBM 9673 Mainframe Computer.

1. Centralized storage, processing, and management for large amounts of data
2. Cost — ½–1½ million dollars
3. 1000s of users
4. Uses

Ø  Governmental agencies

Ø  Large Business corporations

Ø  Airline reservations

Example: IBM System/370, IBM 4300, IBM 9672, NCR 8000, UNIVAC 1100/90 etc.

Minicomputers:

Figure 3.3: PDP8 Minicomputer.

A minicomputer system performs the basic arithmetic and logic functions and supports some of the programming languages used with large computer systems. They are physically smaller, less expensive, and gave a small storage capacity than mainframes. Minicomputers are ideally suited for processing tasks that do not require access to huge volumes of stored data. As a result of their low cost, ease of operation, and versatility, minicomputers have gained rapid acceptance from their introduction in the mid-sixties. Some of the larger and expensive minicomputers are capable of supporting a number of terminals in a time-shared mode. DEC PDP8, DEC PDP11, IBM 134 and DEC VAX, etc. are some examples of Minicomputers.

Workstation:

 

Figure 3.4: Sun Ultra 60 workstation.

Workstations are single user computer with more processing power than personal computers. Such computers have many features of minicomputer but at slightly lower price. Workstations are mainly equipped with one or more processor, specialized processor for mathematics and graphics, high-speed larger size memory and fast disk storage. They also have bigger high-resolution monitor. Workstations are more reliable than personal computers and so popular among scientists, engineers, graphic artists and animators who need to process real time data reliably. Video editing, animations, scientific modeling are few applications of workstations. Sun Ultra 60 is an example of popular workstation. Price of workstations is two to three times than of a personal computer.

Microcomputers:

Microcomputers are microprocessor based small laptop or desktop systems with varying capability depending on the input/ output and secondary storage devices supporting it.

Figure 3.5: Microcomputers.

Subcategories:

1.      Desktop

2.      Notebook

Ø  Single user

General computing tasks:

Ø  Word processing

Ø  E-mail

Ø  Internet access

Hand-held computers or PDA:

Figure 3.6: Handheld Computer.

1. Cost — $100–$700
2. Fit in the palm of people’s hand
3. Run on batteries
4. Uses

Ø  Appointment book

Ø  Address book

Ø  Calculator

Ø  Notepad

—— ○ ——

4. Describe with example various generation of computers.

Ans. to the question no: 4

                                                                    

First Generation Computers (1944-1958)

:

1. They were the fastest calculating devices of their time.
2. They used vacuum tubes.
3. Discrete semiconductor device based with limited system software supported.
4. They were too bulky in size.
5. They should be properly air-conditioned.
6. The power consumption was very high.
7. They were prone to frequent hardware failures.
8. Constant maintenance required.
9. Commercial production of these computers was difficult and costly.
10. They had limited commercial use.

Figure 4.1: UNIVAC — First Generation Computer.

Figure 4.2: Vacuum Tubes.

Example: ENIAC, EDVAC, EDSAC, UNIVAC-I, IBM 701, etc.

Second Generation Computers (1959-1963)

:

1. Ten times faster than the first-generation computers.
2. Used transistors in circuits.
3. Much smaller in size.
4. Consumed much less power.
5. Much more reliable and less prone to hardware failures.
6. Had faster and larger primary and secondary storage devices.
7. Easier to program.
8. Hence they had wider commercial use.
9. High-level programming Languages like FORTRAN, COBOL, ALGOL and SNOBOL were developed.
10.  

Figure 4.3: Transistor.

Third Generation Computers (1964-1970):

1. Much more powerful (Performs 1 million instruction per sec).
2. Used IC (Integrated Circuit) instead of transistors.
3. Much smaller in size.
4. Much less power consumption.
5. Much more reliable and less prone to hardware failures.
6. Faster and larger primary and secondary storage devices.
7. Totally general-purpose machines suitable for both scientific and commercial applications

8. Standardization of high-level programming languages allowed programs written for one computer to be easily ported to and executed on another computer.
9. Timesharing O.S helped in drastically improving the productivity of programmers cutting down the time and cost of program development by several fold.

Figure 4.4: IC.

Fourth Generation Computers (1971-now):

1. Microprocessors came into existence.
2. Starting of Personal Computer Revolution.
3. P.C. Compact and inexpensive
4. Hard disk: Cheaper, smaller in size and larger in capacity
5. Floppy disks became popular.
6. LAN, WAN came into existence.
7. Several O.S like MS-DOS, MS Windows, and UNIX were developed.
8. C, C++ programming became popular.
9. The PCs were much smaller and cheaper than the mainframes or minicomputers of 3rd generation.
10. They are much more powerful.
11. No air-conditioning was required for the PCs
12. Consumed much less power.
13. Much more reliable and less prone to hardware failures.
14. Faster and larger primary and secondary storage devices.
15. Totally general-purpose machines.
16. They contained graphical user interface.
17. Availability of C programming language allowed these systems to be effectively used for systems programming also, like design of compilers and O.S
18. Object-oriented languages allowed rapid software development.
19.  

Figure 4.5: Microprocessor.

Fifth Generation Computers (Now to future):

1. Superconductors like Gallium Arsenide (GaAs₂), which has zero resistance, will be used in computers’ electronic circuits.
2. Larger disk space
3. Optical disks (CD-ROM) emerged.
4. Internet came into existence.
5. The concept of ‘Multithreading’ was introduced.
6. Java programming gained popularity.

7. Portable PCs (notebook computers) are much more smaller and handy.
8. Desktop PCs and workstations are several times more powerful
9. Consume less power
10. Hot pluggable feature.
11. Commercial production of these systems is easier and cheaper.
12. Newer and more powerful applications, including multimedia applications.

13. Internet usage by common man.

Figure 4.6: An IC made by Gallium Arsenide.

Figure 4.7: Fifth Generation Computers.

—— ○ ——

5. What factors determine the type of a computer?

Ans. to the question no: 5

There are seven factors. They are following:

1. Types of CPU;
2. Amount of main memory;
3. Storage capacity;
4. Speed of output device in CPS;
5. Processing speed in MIPS;
6. Number of users;
7. Price.

—— ○ ——

6.       a) Subtract (100)₂ from (1011)₂ using the 1’s/2’s complement method.

          b) Subtract (7)₁₀ from (14)₁₀ using the 1’s/2’s complement method.

          c) Subtract (9)₁₀ from (7)₁₀ using the 1’s/2’s complement method.

          d) Subtract (1010)₂ from (011)₂ using the 1’s/2’s complement method.

Ans. to the question no: 6

a)

1’s complement method

 

Here, the length of 100₂ is not equal to 1011₂ so an extra zero will be added with 100₂ to make the length of both numbers the same.

 

Now,

Taking the 1’s complement of 0100₂ we get, 1011₂, which will be added with 1011₂

 

∴

 

Since, there is an overflow, the result will be positive and this overflow will be added with 0110₂

 

∴

 

∴ The result is (111)₂ using 1’s complement method.

2’s complement method

 

Here, the length of 100₂ is not equal to 1011₂ so an extra zero will be added with 100₂ to make the length of both numbers the same.

Now,

Taking the 1’s complement of 0100₂ we get, 1011₂ and to get 2’s complement of 0100₂, we have to add 1 with 1011₂.

Hence, the 2’s complement of 0100₂ is

 

Now, this 2’s complement 1100₂ will be added with 1011₂

 

∴

 

Since, there is an overflow, the result will be positive

∴ Ignoring the overflow, the result is (111)₂ using 2’s complement method.

b)

1’s complement method

 

Here, the length of 111₂ is not equal to 1110₂ so

3

2

1

2

0

2

1

14

2

0

7

2

1

1

an extra zero will be added with 111₂ to make

∴

the length of both numbers the same.

 

Now,

 

 

Taking the 1’s complement of 0111₂ we get, 1000₂,

which will be added with 1110₂

 

1

2

2

2

1

2

0

1

7

3

1

∴

∴

 

Since, there is an overflow, the result will be positive and this overflow will be added with 0110₂

 

∴

 

∴ The result is (111)₂ using 1’s complement method.

Now, (111)₂ → (7)₁₀

Hence, the result is (7)₁₀ using 1’s complement method.

2’s complement method

 

Here, the length of 111₂ is not equal to 1110₂ so an extra zero will be added with 111₂ to make the length of both numbers the same.

Now,

 

Taking the 1’s complement of 0111₂ we get, 1000₂ and to get 2’s complement of 0111₂, we have to add 1 with 1000₂.

Hence, the 2’s complement of 0111₂ is

 

Now, this 2’s complement 1001₂ will be added with 1110₂

 

∴

 

∴ Ignoring the overflow, the result is (111)₂ using 2’s complement method.

Since, there is an overflow, the result will be positive

 

Now, (111)₂ → (7)₁₀

Hence, the result is (7)₁₀ using 2’s complement method.

c)

1’s complement method

			1

 

Here, the length of 111₂ is not equal to 1001₂ so

2

2

2

0

2

1

9

2

1

4

2

0

0

an extra zero will be added with 111₂ to make

∴

the length of both numbers the same.

 

Now,

 

 

Taking the 1’s complement of 1001₂ we get, 0110₂,

which will be added with 1110₂

 

1

2

2

2

1

2

0

1

7

3

1

∴

∴

 

Since, there is no overflow, the result will be negative. To get the result, we take 1’s complement of 1101₂ and find 0010₂. Attaching a negative sign the result is -0010₂ using 1’s complement method.

Now, -(0010)₂ → -(2)₁₀

Hence, the result is -(2)₁₀ using 1’s complement method.

2’s complement method

 

Here, the length of 111₂ is not equal to 1001₂ so an extra zero will be added with 111₂ to make the length of both numbers the same.

Now,

 

 

Taking the 1’s complement of 1001₂ we get, 0110₂ and to get 2’s complement of 1001₂, we have to add 1 with 0110₂.

Hence, the 2’s complement of 1001₂ is

 

Now, this 2’s complement 0111₂ will be added with 0111₂

 

∴

 

1’s complement

Since, there is no overflow, the result will be negative. To get the result, we take 2’s complement of 1110₂ and find 0010₂.

 

Attaching a negative sign the result is -0010₂ using 2’s complement method.

 

Now, -(0010)₂ → -(2)₁₀

Hence, the result is -(2)₁₀ using 2’s complement method.

d)

1’s complement method

 

Here, the length of 011₂ is not equal to 1010₂ so an extra zero will be added with 011₂ to make the length of both numbers the same.

 

Now,

 

 

Taking the 1’s complement of 1010₂ we get, 0101₂, which will be added with 0011₂

 

∴

 

Since, there is no overflow, the result will be negative. To get the result, we take 1’s complement of 1000₂ and find 0111. Attaching a negative sign the result is -0111₂ using 1’s complement method.

2’s complement method

 

Here, the length of 011₂ is not equal to 1010₂ so an extra zero will be added with 011₂ to make the length of both numbers the same.

Now,

 

Taking the 1’s complement of 1010₂ we get, 0101₂ and to get 2’s complement of 1010₂, we have to add 1 with 0101₂.

Hence, the 2’s complement of 1010₂ is

 

Now, this 2’s complement 0110₂ will be added with 0011₂

 

∴

 

1’s complement

Since, there is no overflow, the result will be negative. To get the result, we take 2’s complement of 1001₂ and find 0111₂.

 

Attaching a negative sign the result is -0111₂ using 2’s complement method.

—— ○ ——

7. Fill in the question marks:

i) (10101010)₂ → (?)₈              ii) (50)₈ → (?)₁₆           iii) (3F)₁₆ → (?)₈

iv) (1110111)₂ → (?)₁₀            v) (40)₈ → (?)₁₆           vi) (A0)₁₆ → (?)₂

vii) (1110111)₂ → (?)₁₆           viii) (40)₈ → (?)₁₀        ix) (A0)₁₆ → (?)₈

x) (1010101)₂ → (?)₁₀             xi) (39)₈ → (?)₁₆          xii) (3F)₁₆ → (?)₂

Ans. to the question no: 7

i) (10101010)₂ → (?)₈ 

Solution:

To convert (10101010)₂ to octal number we have to convert it first into decimal and than we have to convert the decimal number into octal. Then we will get the result.

(10101010)₂ Converting into decimal:

=  1×2⁷ + 0×2⁶  + 1×2⁵ + 0×2⁴ + 1×2³ + 0×2² + 1×2¹ + 0×2⁰

= 1×128 + 0×64 + 1×32 + 0×16 + 1×8 + 0×4 + 1×2 + 0×1

= 128 + 32 + 8 + 2

= 170

LSB

Now (170)_10­ converting into octal:

                 

            8    170

2

                  8   21

5

8

2

                

2

8

0

                        

 

 

MSB

∴ (170)₁₀ = (252)₈

∴ (10101010)₂ = (252)₈

ii) (50)₈ → (?)₁₆

Solution:

To convert (50)₈ to hexadecimal number we have to convert it first into decimal and than we have to convert the decimal number into hexadecimal. Then we will get the result.

(50)₈ Converting into decimal:

=  5×8¹ + 0×8⁰

= 5×8 + 0×1

= 40 + 0

= 40

LSB

Now (40)_10­ converting into hexadecimal:

16

                 

                 40

16

8

2

                    

16

2

0

                

                        

	MSB

 

 

∴ (40)₁₀ = (28)₁₆

∴ (50)₈ = (28)₁₆

iii) (3F)₁₆ → (?)₈

Solution: To convert (3F)₁₆ to octal number we have to convert it first into decimal and than we have to convert the decimal number into octal. Then we will get the result.

(3F)₁₆ Converting into decimal:

= 3×16¹ + 15×16⁰

= 3×16 + 15×1

= 48 + 15

= 63

LSB

Now (63)_10­ converting into octal:

8

                 

                 63

8

7

7

                    

7

0

                

                        

	MSB

 

 

∴ (63)₁₀ = (77)₈

∴ (3F)₁₆ = (77)₈

iv) (1110111)₂ → (?)₁₀

Solution:

(1110111)₂ Converting into decimal:

= 1×2⁶ + 1×2⁵  + 1×2⁴ + 0×2³ + 1×2² + 1×2¹ + 1×2⁰

= 1×64 + 1×32 + 1×16 + 0×8 + 1×4 + 1×2 + 1×1

= 64 + 32 + 16 + 0 + 4 + 2 + 1

= 119

∴ (1110111)₂ = (119)₁₀

v) (40)₈ → (?)₁₆

Solution: To convert (40)₈ to hexadecimal number we have to convert it first into decimal and than we have to convert the decimal number into hexadecimal. Then we will get the result.

(40)₈ Converting into decimal:

=  4×8¹ + 0×8⁰

= 4×8 + 0×1

= 32 + 0

= 32

LSB

Now (32)_10­ converting into hexadecimal:

16

                 

                 32

16

0

2

                    

16

2

0

                

                        

	MSB

 

 

∴ (32)₁₀ = (20)₁₆

∴ (40)₈ = (20)₁₆

vi) (A0)₁₆ → (?)₂

Solution: To convert (A0)₁₆ to binary number we have to convert it first into decimal and than we have to convert the decimal number into binary. Then we will get the result.

(A0)₁₆ Converting into decimal:

= 10×16¹ + 0×16⁰

= 10×16 + 0×1

= 160 + 0

= 160

Now (160)_10­ converting into binary:

2

                 

80

                 160

0

LSB

0

40

2

2

                    

0

                

2

20

                        

			0

 

0

2

5

 

 

∴ (160)₁₀ = (10100000)₂

∴ (A0)₁₆ = (10100000)₂

vii) (1110111)₂ → (?)₁₆

Solution: To convert (1110111)₂ to hexadecimal number we have to convert it first into decimal and than we have to convert the decimal number into hexadecimal. Then we will get the result.

(1110111)₂ Converting into decimal:

= 1×2⁶ + 1×2⁵  + 1×2⁴ + 0×2³ + 1×2² + 1×2¹ + 1×2⁰

= 1×64 + 1×32 + 1×16 + 0×8 + 1×4 + 1×2 + 1×1

= 64 + 32 + 16 + 0 + 4 + 2 + 1

= 119

∴ (1110111)₂ = (119)₁₀

Now (119)_10­ converting into hexadecimal:

 

∴ (119)₁₀ = (77)₁₆

∴ (1110111)₂ = (77)₁₆

viii) (40)₈ → (?)₁₀

Solution:

(40)₈ Converting into decimal:

=  4×8¹ + 0×8⁰

= 4×8 + 0×1

= 32 + 0

= 32

∴ (40)₈ = (32)₁₀

ix) (A0)₁₆ → (?)₈

Solution: To convert (A0)₁₆ to octal number we have to convert it first into decimal and than we have to convert the decimal number into octal. Then we will get the result.

(A0)₁₆ Converting into decimal:

= 10×16¹ + 0×16⁰

= 10×16 + 0×1

= 160 + 0

= 160

Now (160)_10­ converting into octal:

8

                 

8

20

                 160

4

LSB

0

2

8

                    

2

                

8

0

                        

 

 

∴ (160)₁₀ = (240)₈

∴ (A0)₁₆ = (240)₈

x) (1010101)₂ → (?)₁₀

Solution:

(1010101)₂ Converting into decimal:

= 1×2⁶ + 0×2⁵  + 1×2⁴ + 0×2³ + 1×2² + 0×2¹ + 1×2⁰

= 1×64 + 0×32 + 1×16 + 0×8 + 1×4 + 0×2 + 1×1

= 64 + 0 + 16 + 0 + 4 + 0 + 1

= 85

∴ (1010101)₂ = (85)₁₀

xi) (39)₈ → (?)₁₆

Solution:

(39)₈  cannot be converted into hexadecimal number because the digits, which are included in octal number system are 0, 1, 2, 3, 4, 5, 6 and 7 and obviously 9 is not a number of octal number system. So 39 cannot be an octal number. So it is absurd to convert 39 into hexadecimal or any other number.

xii) (3F)₁₆ → (?)₂

Solution: To convert (3F)₁₆ to binary number we have to convert it first into decimal and than we have to convert the decimal number into binary. Then we will get the result.

(3F)₁₆ Converting into decimal:

= 3×16¹ + 15×16⁰

= 3×16 + 15×1

= 48 + 15

= 63

Now (63)_10­ converting into binary:

2

                 

31

                 63

1

LSB

1

15

2

2

                    

1

                

2

7

                         

			1

 

1

2

1

 

 

∴ (63)₁₀ = (111111)₂

∴ (3F)₁₆ = (111111)₂

—— ○ ——

8. Convert (12.525)₁₀ to Octal/Binary number.

Ans. to the question no: 8

Solution:

Converting (12.525)₁₀ into Octal:

(12)₁₀              Octal                                                                   (.525)₁₀          Octal

 

                                                                                   

                                                                                                                                   

                                                                                                   0.525×8 = 4.2                         4

                                                                                                   0.2×8     =1.6                         1

LSB

MSB

1

4

0

1

12

8

8

                                                                                                   0.6×8     = 4.8                        4

                                                                                                   0.8×8     = 6.4                        6

                                                                                                   0.4×8     = 3.2                        3

∴  (12)₁₀ = (14)₈                                                                                               0.2×8     = 1.6                        1

LSB

                                                                                                   

                                                                                                  ∴ (.525)₁₀ = (414631)₈

∴ (12.525)₁₀ = (14.414631)₈

Converting (12.525)₈ into Binary:                                                  

(12)₁₀                   Binary                                                                               (.525)₁₀              Binary

					LSB

 

                                                                                                   0.525×2 = 1.05                         1

0

                                                                                                 

                                                                                                   0.05×2   = 0.1                           0

0

2

2

0

1

2

12

3

6

2

                                                                                                 

1

                                                                                                   0.1×2     = 0.2                           0

1

                                                                                                  

                                                                                                   0.2×2     = 0.4                            0    

MSB

                                                                                                  

                                                                                                   0.4×2     = 0.8                            0

                                                                                                  

                                                                                                   0.8×2     = 1.6                            1

	LSB

 

                                                                                                     ∴ (.525)₁₀ = (100001)₂

∴  (12)₁₀  = (1100)₂

∴ (12.525)₁₀ = (1100.100001)₂

—— ○ ——

9. How (-25)₁₀, (-57)₁₀, (-28)₁₀, (- 40)₁₀ will be stored in an 8-bit RAM?

Ans. to the question no: 9

Solution:

(-25)₁₀ is stored in a 8-bit RAM by this way,

First (-25)₁₀ will  be converted into Binary.

	LSB

 

So,

 

0

                                                                    

 

So, -(25)₁₀ = -(11001)₂

As the number is negative, so, to store -(11001)₂ in 8-bit RAM we have to take the 2’s complement of the number.

 

So, 11001 → 00110

2’s complement

                           + 1

 

So, (00111)₂ that means -(25)₁₀ will be stored in 8-bit RAM like shown below.

1

0

0

0

0

1

1

1

Sign bit

                  

Figure1-8bit RAM

(-57)₁₀ is stored in a 8-bit RAM by this way,

First (-57)₁₀ will  be converted into Binary.

	LSB

 

So,

 

0

                                                                    

 

MSB

So, -(57)₁₀ = -(111001)₂

As the number is negative, so, to store -(111001)₂ in 8-bit RAM we have to take the 2’s complement of the number.

 

So, 111001 → 000110

2’s complement

                              + 1

 

So, (000111)₂  that means -(57)₁₀ will be stored in 8-bit RAM like shown below.

1

0

0

0

0

1

1

1

Sign bit

                  

Figure1-8bit RAM

(-28)₁₀ is stored in a 8-bit RAM by this way,

First (-28)₁₀ will  be converted into Binary.

	LSB

 

So,

 

1

                                                                    

 

So, -(28)₁₀ = -(11100)₂

As the number is negative, so, to store -(11100)₂ in 8-bit RAM we have to take the 2’s complement of the number.

 

So, 11100 → 00011

2’s complement

                           + 1

 

So, (00100)₂ that means -(28)₁₀ will be stored in 8-bit RAM like shown below.

1

0

0

0

0

1

0

0

Sign bit

                  

Figure1-8bit RAM

(-40)₁₀ is stored in a 8-bit RAM by this way,

First (-40)₁₀ will  be converted into Binary.

	LSB

 

So,

 

0

                                                                    

 

So, -(40)₁₀ = -(101000)₂

As the number is negative, so, to store -(101000)₂ in 8-bit RAM we have to take the 2’s complement of the number.

 

So, 101000 → 010111

2’s complement

                               + 1

 

So, (011000)₂ that means -(40)₁₀ will be stored in 8-bit RAM like shown below.

1

0

0

1

1

0

0

0

Sign bit

                  

Figure1-8bit RAM

—— ○ ——

10. What is BCD? Represent (15)₁₀, (253)₁₀ in BCD.

Ans. to the question no: 10

BCD: BCD is the shortcut of Binary Coded Decimal, which is a coding scheme used to represent decimal numbers only. In BCD a decimal number is not converted to binary rather each digit of the number is replaced by its binary equivalent.

Decimal and binary equivalent

Decimal                                        Binary	Decimal                                         Binary
0                                               0000	5                                                 0101
1                                               0001	6                                                 0110
2                                               0010	7                                                 0111
3                                               0011	8                                                 1000
4                                               0100	9                                                 1001

As compared to binary, BCD codes use lots of bits to represent a decimal number. BCD is used because; it does not require any conversion of decimal numbers just each digit is replaced. Conversion to binary requires a fair amount of calculation for a digital system to use binary. Computers have great computing power and so use binary. But small digital systems (like pocket calculator) cannot afford the computation and so use BCD.

(15)₁₀ will be represented in BCD as:

1                      5

                                                                       

                                                                    0001                0101

So, (15)₁₀ ≡ 00010101_BCD

(253)₁₀ will be represented in BCD as:

2                      5                      3

 

                                                        0010                0101                0011

So, (253)₁₀ ≡ 001001010011_BCD

—— ○ ——

11. Describe all Logic gates, their symbols, truth table.

Ans. to the question no: 11

Logic Gates: Computers work on an electrical flow where a high voltage is considered a 1 and a low voltage is considered a 0.  Using these highs and lows, data is represented.  Electronic circuits must be designed to manipulate these positive and negative pulses into meaningful logic. Logic gates are the building blocks of digital circuits.  Combinations of logic gates form circuits designed with specific tasks in mind. Basic Logic Gates are:

1. NOT,
2. AND,
3. NAND,
4. OR,
5. NOR,
6. XOR and
7. XNOR.

The AND Gate:

The AND gate implements the AND function. With the gate shown to the left, both inputs must have logic 1 signals applied to them in order for the output to be a logic 1. With either input at logic 0, the output will be held to logic 0.

A   Input A	Input B	Output Q
Inputs   Outputs   0	0	0
Q   0	1	0
B   1	0	0
1	1	1

Figure 11.1: Truth Table and Symbol for AND Gate.

There is no limit to the number of inputs that may be applied to an AND function, so there is no functional limit to the number of inputs an AND gate may have. However, for practical reasons, commercial AND gates are most commonly manufactured with 2, 3, or 4 inputs. A standard Integrated Circuit (IC) package contains 14 or 16 pins, for practical size and handling. A standard 14-pin package can contain four 2-input gates, three 3-input gates, or two 4-input gates, and still have room for two pins for power supply connections.

The OR Gate:

A   Outputs   Q   Input A	Input B	Output Q
Inputs   0	0	0
0	1	1
B   1	0	1
1	1	1

Figure 11.2: Truth Table and Symbol for OR Gate.

The OR gate is sort of the reverse of the AND gate. The OR function, like its verbal counterpart, allows the output to be true (logic 1) if any one or more of its inputs are true. This is correctly reflected by the basic OR function. In symbols, the OR function is designated with a plus sign (+). In logical diagrams, the symbol to the left designates the OR gate. As with the AND function, the OR function can have any number of inputs. However, practical commercial OR gates are mostly limited to 2, 3, and 4 inputs, as with AND gates.

The NOT Gate, or Inverter:

 

Q   Inputs   A   Outputs   Input A	Output Q
0	1
1	0

Figure 11.3: Truth Table and Symbol for NOT Gate.

The inverter is a little different from AND and OR gates in that it always has exactly one input as well as one output. Whatever logical state is applied to the input, the opposite state will appear at the output. The NOT function, as it is called, is necessary in many applications and highly useful in others. The NOT function is denoted by a single bar mark ( ¯ ) may also be used for this purpose: 0  and . In the inverter symbol, the triangle actually denotes only an amplifier, which in digital terms means that it "cleans up" the signal but does not change its logical sense. It is the circle at the output, which denotes the logical inversion. The circle could have been placed at the input instead, and the logical meaning would still be the same.

The NAND Gate:

Inputs   B   A   Input A	Input B	Output Q
Outputs   0	0	1
Q   0	1	1
1	0	1
1	1	0

Figure 11.4: Truth Table and Symbol for NAND Gate.

The NAND gate implements the NAND function, which is exactly inverted from the AND function you already examined. With the gate shown to the left, both inputs must have logic 1 signals applied to them in order for the output to be a logic 0. With either input at logic 0, the output will be held to logic 1. The circle at the output of the NAND gate denotes the logical inversion, just as it did at the output of the inverter. As with AND, there is no limit to the number of inputs that may be applied to a NAND function, so there is no functional limit to the number of inputs a NAND gate may have. However, for practical reasons, commercial NAND gates are most commonly manufactured with 2, 3, or 4 inputs, to fit in a 14-pin or 16-pin package.

The NOR Gate:

Input A	Input B	Output Q
Inputs   Q   B   A   Outputs   0	0	0
0	1	1
1	0	1
1	1	1

Figure 11.5: Truth Table and Symbol for NOR Gate.

The NOR gate is an OR gate with the output inverted. Where the OR gate allows the output to be true (logic 1) if any one or more of its inputs are true, the NOR gate inverts this and forces the output to logic 0 when any input is true.

In symbols, the NOR function is designated with a plus sign (+), with an over bar over the entire expression to indicate the inversion. In logical diagrams, the symbol to the left designates the NOR gate.

As expected, this is an OR gate with a circle to designate the inversion. The NOR function can have any number of inputs, but practical commercial NOR gates are mostly limited to 2, 3, and 4 inputs, as with other gates in this class, to fit in standard IC packages.

The Exclusive-OR, or XOR Gate:

A   Input A	Input B	Output Q
Outputs   Inputs   0	0	0
Q   0	1	1
B   1	0	1
1	1	0

Figure 11.6: Truth Table and Symbol for XOR Gate.

The Exclusive-OR, or XOR function is an interesting and useful variation on the basic OR function. Verbally, it can be stated as, "Either A or B, but not both." The XOR gate produces a logic 1 output only if its two inputs are different. If the inputs are the same, the output is a logic 0. The XOR symbol is a variation on the standard OR symbol. It consists of a plus (+) sign with a circle around it; that is ⊕. The logic symbol, as shown here, is a variation on the standard OR symbol. Unlike standard OR/NOR and AND/NAND functions, the XOR function always has exactly two inputs, and commercially manufactured XOR gates are the same. Four XOR gates fit in a standard 14-pin IC package.

XNOR (Exclusive-NOR) gate:

A   Input A	Input B	Output Q
Outputs   0	0	1
Q   B   Inputs   0	1	0
1	0	0
1	1	1

Figure 11.7: Truth Table and Symbol for XNOR Gate.

If a NOT is attached to the output of an XOR gate, an XNOR gates is formed. XNOR gate produces an output of 1 when there are even (or zero) number of 1 in the input. Otherwise, the output is 0. The symbol used for XNOR gate and truth table is shown in Figure . XNOR operation sometimes is denoted by ⊙ symbol. XNOR gates can only have 2 inputs.

—— ○ ——

12. What is scan code? Write the binary of ASCII value for uppercase & lowercase characters.

Ans. to the question no: 12

Scan Code: The code a keyboard sends on each key-press and release is unique for each key on the keyboard. This code is known as scan code.

Under the keys of a keyboard, there is a circuit board containing a processor and few other support chips. Keys are actually switches arranged in rows and columns. When a switch is pressed or released it produces an electric signal along particular row and column. The processor receives the signal and locates the position of the key. It then sends a predefined binary code to the computer. After receiving the code, it is then job of the processing devices (of system unit) to process that code.

Scan codes are unique; so Shift keys on the left and right have different scan code values. Similarly, the digit keys on the topside and on the numeric keypad have different scan codes.

The binary of ASCII (American Standard Code for Information Interchange) value for uppercase and lowercase characters are shown in the table below:

Uppercase Characters	Decimal Equivalent	ASCII Code in binary value	Lowercase Characters	Decimal Equivalent	ASCII Code in binary value
A	065	01000001	a	097	01100001
B	066	01000010	b	098	01100010
C	067	01000011	c	099	01100011
D	068	01000100	d	0100	01100100
E	069	01000101	e	0101	01100101
F	070	01000110	f	0102	01100110
G	071	01000111	g	0103	01100111
H	072	01001000	h	0104	01101000
I	073	01001001	i	0105	01101001
J	074	01001010	j	0106	01101010
K	075	01001011	k	0107	01101011
L	076	01001100	l	0108	01101100
M	077	01001101	m	0109	01101101
N	078	01001110	n	0110	01101110
O	079	01001111	o	0111	01101111
P	080	01010000	p	0112	01110000
Q	081	01010001	q	0113	01110001
R	082	01010010	r	0114	01110010
S	083	01010011	s	0115	01110011
T	084	01010100	t	0116	01110100
U	085	01010101	u	0117	01110101
V	086	01010110	v	0118	01110110
W	087	01010111	w	0119	01110111
X	088	01011000	x	0120	01111000
Y	089	01011001	y	0121	01111001
Z	090	01011010	z	0122	01111010

—— ○ ——

13. Name keyboard connectors.

Ans. to the question no: 13

Keyboards are connected with the CPU via connectors, which are called keyboard connectors. The followings are the names of common keyboard connectors –

Ø  5–pin DIN (Deustche Industrie Norm) connector

Ø  6–pin IBM PS/2 mini-DIN connector

Ø  4–pin USB (Universal Serial Bus) connector

 

Figure 13.1: 5–pin DIN (Deustche Industrie Norm) connector.

Figure 13.2: 6–pin IBM PS/2 mini-DIN connector.

 

Figure 13.3: 4–pin USB (Universal Serial Bus) connector.

Normal DIN connectors are becoming obsolete. They are being replaced with smaller size mini-DIN PS/2 connectors. Newer keyboards are coming with USB connectors. Regardless of the connector used, the connecting cable has wires to carry power supply and scan codes. Power is supplied to a keyboard from the system unit, but scan code data are transferred from the keyboard to the system unit. (Technically the reverse flow is also possible.) There are also wireless keyboards.

—— ○ ——

14. Describe all the keys in a keyboard with types and use.

 

Ans. to the question no: 14

Types And Uses of All The Keys on A Keyboard:

The keyboard is the primary way of entering text in a computer. The personal computers, which we are using today, have 101 to 105 keys. The IBM Enhanced standard keyboard is the most popular keyboard today. It contains 101 keys. Figure 14.1 shows the IBM Enhanced standard keyboard.

 

Figure 14.1: The IBM Enhanced standard keyboard

Types of Keys:

            Different keys of a keyboard have different functions and uses. The keys, which are contained in on a keyboard (for example, The IBM Enhanced standard keyboard), are classified in five types and these are:

1. Alphanumeric keys

2. Numeric keypad

3. Function keys

4. Modifier keys

5. Cursor-movement keys

Alphanumeric Keys: The Alphanumeric keys are:

Ø  Letters of the English alphabet from a to z;

Ø  Decimal digits 1, 2, 3… etc.;

Ø  Punctuation marks such as comma, semicolon, full stop, question mark etc.

Ø  Some special symbols for example, braces, hash (#), dollar sign (&), percentage sign (%) etc.,

Ø  Special characters for example, Space bar, Enter, Tab Caps Lock and Backspace;

            Alphanumeric keys remain from the second to fifth rows on the keyboard from the top. These keys are used to input characters (letters from a to z), digits, punctuation signs and some other special symbols. The alphanumeric keys are like the keys of an ordinary typewriter machine. The second row contains the keys of decimal digits and other common symbols (such as @, #, &, $ etc.). The letters of English alphabet and punctuation marks are on the third, fourth and fifth rows from the top. There are few other keys in alphanumeric group that have special use. They are the following:

           

Ø  Tab:

1.      The Tab key is used to move the current typing position that is the cursor or the insertion point (on the screen) by a predefined amount.

2.      In dialog boxes it moves the focus of default key-press into different buttons.

3.      Tab is often used to switch between two or more running programs or to go one program from another without using mouse.

Ø  Caps Lock:  The Caps Lock key is used to type capital letters of English alphabet.

Ø  Space bar:

1.      It is used to give spaces between two letters during typing.

2.      Sometimes space bar is used to assign tick (ü) marks in dialog boxes or menus.

Ø  Enter:

1.      In text editor programs the Enter key ends the current text line and starts a new one.

2.      It usually finishes a command or data entry or executes the final command.

3.      In dialog boxes or popup menus it executes a given command.

4.      Without using mouse the Enter key can be used to give the command ‘OK’ in dialog boxes.

5.      In MS-DOS the Enter key executes the command after writing the command.

6.      During browsing the Internet the Enter key is pressed after typing the web address in the address bar.

Ø  Backspace: The Backspace key erases the last typed word, which is useful in editing any text writing.

Cursor Movement Keys:

The small blinking mark on the screen that indicates the point of current text input is called cursor. The cursor control keys are in the middle of the Alphanumeric Keys and the Numeric Keypad and these are the left, right, up and down arrows, the Home, End, Page Up and the Page Down keys. These keys are used to move the cursor across the screen. The Home key sends the cursor at the beginning of the current text line and the End key sends the cursor at the end of the current text line. The Page Up and the Page Down keys move a page full of text or graphics up and down respectively.

Numeric Keypad:

1.      The numeric keypad exists on the very right side of the keyboard and is used for numeric inputs.

2. The layout of the numeric keypad is just like the ordinary calculators, which is helpful to input data quickly.

3. It contains the 10 decimal digits, the decimal point (.), the Num Lock key and some keys of mathematical symbols such as addition (+), subtraction (-), multiplication (*) and division (/).
4. At the right top of the Numeric Keypad a key named Num Lock is remained. When the Num Lock key is on, the Numeric Keypad is activated and when it is off, the numeric keypad is deactivated. A Status LED for the Num Lock key, which indicates the activated or deactivated situation of the Numeric keypad, is situated at just above of the Num Lock key. When the LED is on, the Numeric Keypad is activated and when the LED is off, the Numeric Keypad is deactivated.

5. When the Numeric Keypad is deactivated that means the LED is off, the keys 4, 6,8 and 2 work as just like the left, right, up and down arrow keys and the keys 7, 9, 1 and 3 work as just like the Home, Page Up, Page Down and End keys.

Function Keys:

On the top of the keyboard in the first row the keys labeled from F1 to F12 are called Function Keys. These keys have different functions in different application programs. The uses of some of the Function Keys are described below:

Ø  The F1 key is generally used to view help in any application program.

Ø  The F2 key is used to rename the selected icon of any file or folder.

Ø  The F3 key is used to show the Search Window, which searches files and folders.

Ø  The F5 key is used to refresh the screen.

Ø  The F8 key is used to enter the Windows in “Safe Mode” after booting the PC.

Ø  The F11 key is used to view full screen the windows of some application programs.

Ø  The F12 key is used to execute the input of the “Save As” command.

Modifier Keys:

Modifier Keys modify the usual functions of other keys and creates the opportunity to make more commands using same keys. Any key those functions for an individual command can be functioned for multiple commands. These keys need to be pressed and held down while other keys are pressed. The names and uses of some Modifier Keys are given below:

Ø  Ctrl: The Ctrl (Control) key is used for command input in association with other keys in editing and formatting texts and various kinds of tasks. For example, to copy any text, graphics, file and folder, we have to press Ctrl and C (Ctrl + C) that means we have to press and hold down Ctrl first and then to press C. There are two Ctrl keys on the keyboard, which have same use.

Ø  Alt: The function of the Alt (Alternative) key is almost same as the Ctrl key. Traditionally, Alt key is programmed to active some menus, or selecting an item from the menu. For example, to open File menu, Alt + F has to be pressed. However, there are some complex functions of Alt key, when it is pressed in association of Ctrl to execute some complex commands, such as Ctrl + Alt + Delete to open the program Windows Task Manager. Two Alt keys on the keyboard have the same function.

Ø  Shift: There are two Shift keys on the keyboard having the same function. Shift key converts an Alphanumeric Key, which is a lowercase English alphabet into an uppercase alphabet. However, the Shift key is also used to execute the functions done by the Ctrl and Alt key when it is pressed in conjunction with them. For example, to select some texts to the end of the document from any part of the document, the Ctrl + Shift + End has to be pressed.

Special Keys: There are some special keys on the IBM keyboard and they are:

Ø  Esc: The Esc (Escape) key is situated at the top left of the keyboard. It is used to cancel a command and to close a dialog box and popup menus.

Ø  Delete: It is used to erase a character, which is at the left side of the cursor. It functions like the Backspace key. An important function of Delete key is, after booting the PC the Delete key is pressed to enter the BIOS (Basic Input/Output System).

Ø  Insert: The Insert key controls whether the text typed will overwrite the current text line or not. If it is on, subsequent characters are inserted into the current cursor position and the text on the right side of cursor are pushed further right. Status of the Insert is not indicated on the keyboard and only a program can make use of it.

Ø  Print Screen: The Print Screen key is used to print any graphics or the sceneries that is shown in the monitor screen.

Ø  Scroll Lock: The Scroll Lock had the use of locking scrolling of large amount of running text. This key has now been depreciated and still found on keyboards for unknown reason.

Ø  Pause: The Pause key pauses the execution of running program. This is useful in diagnosis of hardware problems.

In fact, there are some more keys are available in today’s computers such as Power, Sleep, Wake and Multimedia keys etc.

—— ○ ——

15. Describe the types and working of scanner with diagram.

Ans. to the question no: 15

Scanners: Scanners allow a PC to convert a drawing or photograph into code that a graphics or desktop publishing program can use to display the image on the screen, to reproduce the image with a graphics printer.

Types of Scanners: Three types of scanners are available.

1. Flatbed Scanner

2. Handheld Scanner

3. Drum Scanner

Figure 15.1: Flatbed Scanner

Figure 15.2: Drum Scanner

Working Mechanism of a Scanner:

Figure 15.3: Working of a Scanner

A scanner works much like a photocopy machine. The document to scan is placed on the top of a glass plate and covered by a white cover. Under the glass plate, is scanning head. The scanning head is comprised of a lamp and an array of sensors. The sensors are known as CCDs (Charge Coupled Devices). The CCDs are arranged in an array so that the width of the document can be covered. When the lamp is illuminated, an optical image of a thin slice of the document is produced on a mirror. After two or three optional reflections, the image is passed through a lens and projected on the CCD sensors. These sensors convert the image into digital signals. As there are finite number of sensors, the thin slice of the document that looks continuous to human eyes, gets divided into small dots, called pixels. To scan the entire document, the scanning head is moved in vertical direction in small steps, and in each step a thin slice of the document gets scanned. Scanning a whole page of a document is called a pass. Some scanners use multiple passes to improve image quality. CCDs are inherently insensitive to colors. So to scan a color document, prior to project the optical image on sensors, it is split into RGB (red, green, blue) components. These components are sensed by the sensor-array separately, and then the on-board processor combines them digitally to produce a color image.

—— ○ ——

16. Describe different types of monitor, their working process and scanning process.

Ans. to the question no: 16

Monitor:

A monitor is simply a physical display device that allows one to see what the computer is doing.  Monitors come in many different sizes.

CRT Monitors:

           

Figure 16.1:CRT Monitor and scanning process

A standard monitor screen is a CRT (cathode ray tube). The screen is coated on the inside surface with dots of chemicals called phosphors. When a beam of electrons hits a dot, the dot will glow. 

On a color monitor these phosphor dots are in groups of three: Red, Green, and Blue. This RGB system can create all the other colors by combining what dots are aglow.

There are 3 signals that control the 3 electron beams in the monitor, one for each RGB color. Each beam only touches the dots that the signal tells it to light. All the glowing dots together make the picture that you see. The human eye blends the dots to "see" all the different colors.

A shadow mask blocks the path of the beams in a way that lets each beam only light its assigned color dots.

LCD screen monitor or flat panel monitor:

Figure 16.2: LCD Monitor and its Scanning Process

LCD (Liquid Crystal Display) screens use an entirely different technique. The screen is still made of dots but is quite flat. LCD displays are made of two layers of a polarizing material with a liquid crystal solution in between. An electrical signal makes the crystals line up in a way that keeps light from going through entirely or just partly. A black screen has all the crystals lined up so that no light gets through. A color LCD screen uses groups of 3 color cells instead of 3 phosphor dots. The signal for a picture cleverly lets just the right spots show their colors. Human eye does the rest.

—— ○ ——

17. Describe different types of printers, their working process and comparison.

Ans. to the question no: 17

Types of Printers: Basically two types of printers are available. They are:

1. Impact Printers, and
2. Non-Impact Printers

Impact Printers: With this type of printer something strikes paper & ribbon together to form a character, like a typewriter.

Types of Impact Printers:

Ø Daisy-wheel Printers:

These printers have print heads composed of metallic or plastic wheels cut into petals. Each petal has the form of a letter (in capital and lower-case), number, or punctuation mark on it. When the petal is struck against the printer ribbon, the resulting shape forces ink onto the paper. Daisy-wheel printers are loud and slow. They cannot print graphics, and cannot change fonts unless the print wheel is physically replaced. With the advent of laser printers, daisy-wheel printers are generally not used in modern computing environments.

                                  

     Figure 17.1: Daisy-wheel Printers                                        Figure 17.2: Petals

Advantages:    Best print quality

Disadvantages: 

1. Very slow - 20 to 80 cps.
2. Only one font can be used at a time.
3. Cannot print graphics.

Ø  Dot Matrix Printer:

Figure 17.3: Dot Matrix Printer

Pins fired at a ribbon, producing dots on the paper, form characters. Using more and smaller pins produces higher resolution output. Two standards have emerged 9-pin and 24-pin. Dot matrix printers typically print up to 200 characters per second in draft mode. They usually have a slower higher resolution (NLQ - Near Letter Quality) mode. Graphics are possible as is color with a special four-color ribbon.

Figure 17.4: Working process of Dot Matrix Printer

One application of dot matrix printers is in POS terminals where they are used to print the itemized receipt for a customer. Multi-part stationery is used and the second copy is retained at the till to provide an audit trail.

Forms characters using row(s) of pins, 9, 18, or 24, which impact the ribbon on top of the paper. Also called pin printers. The more pins, the smoother looking the characters.

Most dot matrix printers have the characteristics below:

Bi-directional:            prints left to right and also right to left

Tractor feed:             uses sprockets to pull continuous-feed paper

Friction feed:             uses pressure to pull single sheets

Advantages:

1. Inexpensive
2. Can does multi-copy forms

Disadvantages:

1. Can be slow
2. Loud
3. Graphics of low quality, if possible at all

Non-Impact Printers: This type of printer does not involve actually striking the paper. Instead, it uses ink spray or toner powder.

Types of Non-Impact Printers:

Ø  Ink-Jet Printer:

 

Figure 17.5: Ink-Jet Printer

Ink Jet printers work by firing small bubbles of ink from a series of jets. The dots formed when the ink hits the paper build up the image. Ink Jet printers are faster than a dot matrix printer, and the quality of the image formed is much better although it can depend on the paper used. If the paper is not absorbent then the ink will smear. Ink jet printers have a resolution of 300 dots per inch although in practice if the ink smears, the final result is not this good. The inks are water based and will run if the paper gets wet.

Good quality color is available with many monochrome printers having a color upgrade option. Color printing is more economical when there is a separate black cartridge; otherwise black has to be produced by mixing all three colors. Since color cartridges are more expensive than black this adds to the cost.

A monochrome ink-jet printer does not cost much more than a dot matrix to buy, but the running costs are much greater. The ink cartridges are expensive and it may be necessary to buy special high quality absorbent paper to obtain the best results.

Ink jet printers are non-impact and are therefore quiet in operation. They are an option when high quality output is required, but the total amount of output does not justify the cost of a laser printer. Most ink jet printers use cut sheet stationery some can be adapted to take continuous stationery. Like the dot matrix printer, they produce text one character at a time.

Advantages:   

1. Quiet
2. High quality text and graphics
3. Some can do color.

Disadvantages: 

1. Cannot use multiple-copy paper
2. Ink can smear

Ø  Laser Printers:

Laser printers set up the image of the complete page before printing. This means that there is an initial delay while the page is processed but once printing starts the page is completed within a second or so. For this reason we call laser printers page printers.

The image is formed by small particles of toner that are distributed electro-statically on the paper. The laser is used to build up a pattern of charge on a roller that then transfers the toner to the paper. The toner is then heated so that it melts onto the paper forming a permanent image.

Figure 17.6: Laser printers

The resolution of a typical laser printer is 600 dots per inch. This refers to the number of dots per inch used when the laser beam marks out the pattern of electric charge that is used to distribute the toner. If the toner particle size is too large then the effective resolution is reduced but a laser printer still produces the highest quality output of all the printers described. Special fine tone toner is used to obtain the best results in laser printers.

The initial cost of buying a laser printer is two to three times that of an ink jet. The running costs are however much less. In addition laser printers can print overhead transparencies and they have a higher print speed compared to an ink jet.

Laser printers are non-impact and all of them use cut sheet paper. Because of the way that they produce the image it would be very expensive to produce a laser printer handling large size paper. Most will take A4 paper and it is possible to buy an A3 laser printer. Color is also an expensive option.

Laser printers are used when high quality output is required and there is sufficient output to justify the initial outlay or where speed of printing is important. The quality is sufficiently good for CAD applications but these often require output to sheets larger than the A4 that the normal laser printer can handle.

Comparison Between Printers:

Printer Type	Technology	Advantage	Disadvantage	Typical Speed
Daisy-wheel Printers	Characters are fully formed on the “petals”, like typewriter keys.	Best print quality.	Cannot print graphics; Very slow; Only one font can be used at a time.	20 to 80 CPS (Characters Per Second).
Dot Matrix Printer	Print head contains a cluster of pins. The pins press an inked ribbon against the paper, creating an image.	Cheaper in price; Can print multi-copy forms.	Slow; Loud; Low quality Graphics.	500 CPS.
Ink-Jet Printer	Electro-statically charged drops hit paper.	Quiet; Prints color; Less expensive; Fast.	Relatively slow; Clogged jets; Lower DPI (Dots Per Inch).	Several hundred characters per second.
Laser Printer	Laser beam directed onto a drum, “etching” spots that attract toner, which is then transferred to paper.	Quiet; Excellent quality; Very high speed; Color/black and white.	High Cost.	Up to several hundred pages per minute.

—— ○ ——

18. A 2.5” square image was scanned with resolution 350 ppi. If we are using 5 bit to represent this image, how much space it would need to be stored in the computer? Leave your answer in KB, MB, Kb, Mb, GB, Gb.

Ans. to the question no: 18

The total area of the image is 2.5×2.5 = 6.25 square inch.

So the whole area in pixels is 6.25×350 pixels as 350 pixels per inch.          

 

2.5”

= 2187.5 pixels

Since we are using 5bit memory to represent this image so it will take

	2.5”

 

2187.5×5 = 109375 bits

Hence 109375-bit memory would need to store the image in the computer.

Now, the answer in KB (kilobyte) is

8 Bit = 1 Byte 1024 Bytes = 1 KB 1024 KB = 1 MB 1024 MB = 1 GB

 Byte

= 13671.875 Byte

Or,  KB

= 13.35 KB

Now, the answer in MB (Megabyte) is

1000bit = 1Kb 1000 Kb = 1Mb 1000 Mb = 1 Gb

Or,  MB

= 1.40625 MB

= 0.013 MB

Now, the answer in GB (Gigabyte) is

Or,  GB

= 0.000012731 GB

Now, the answer in Kb (Kilobit) is

 Kb

= 109.375 Kb

Now, the answer in Mb (Megabit) is

Mb

= 0.109375 Mb

Now, the answer in Gb (Gigabit) is

 Gb

= 0.00109375 Gb

—— ○ ——

19. Resize a 1024´768 image with same aspect ratio and width of 480.

Ans. to the question no: 19

Here the ratio =

      Given that width = 480

      Let, height = x

     

      According to the rule,

     

     

So, 1024×768 size in imaged into width of 480. Then the size of the image will be 480×360.

—— ○ ——

20. A 15” color monitor has aspect ratio of 4:3. Calculate the actual length and width of any image (in pixels) that fits exactly with the monitor. Your monitor’s resolution is 768´624 ppi.

Ans. to the question no: 20

Let, the length is x and the width is y.

So, the aspect ratio is   __________(1)           

Hypotenuse

Since the monitor is given that 15”

 

15”

So its length of the diagonal is 15”

	Perpendicular

 

Now from the Pythagoras’ theorem,

 

(Hypotenuse)² = (Base)² + (Perpendicular)²

Figure 20.1

∴ 15² = y² + x²________________________(2)

Again from equation (1),

 and

Now, putting the value of x in equation (2) we find

Hence, the width is 12 inch.

Now, putting y = 12 in equation (2) we find

Hence, the length is 9 inch.

Given that, resolution is 768´624 ppi.

So the width in pixels will be 12×768 = 9216 pixels

And the length in pixels will be 9×624 = 56616 pixels

Hence, the actual length and width of any image (in pixels) that fits exactly with the monitor is

Length = 9216 pixels

Width = 56616 pixels

—— ○ ——

21. Draw and label the block diagram of m - processor and computer hardware.

Ans. to the question no: 21

Block Diagram of m - Processor (Microprocessor):

 

Block Diagram of Computer Hardware:

 

—— ○ ——

22. Define Software. Draw the hierarchical model of S/W with examples of each.

Ans. to the question no: 22

Software:

Software is a set of electronic instructions that tells the computer how to do certain tasks. A set of instructions is often called a program.

Software of a computer system is intangible rather than physical. It is the term used for any type of program. Software consists of statements, which instruct a computer to perform the required task. Without software a computer is simply a mass of electronic components. For a computer to input, store, make decisions, arithmetically manipulate and output data in the correct sequence it must have access to appropriate programs. Thus, the software includes all the activities associated with the successful development and operation of the computing system other than the hardware pieces. Hardware does the actual computing, and the software drives the computer. Figure 22.1 shows the communication between users and hardware, Software plays the role to connect the users and the hardware. The application software conveys the user intention to system software and the system software transfers and translates the intention for the hardware.

 

Figure 22.1

Hierarchical Model of Software:

 

Figure 22.2: Hierarchical model of Software.

System Software

:

System software refers to programs that assist the users to generate, debug, test modify application programs, and then to execute them. System software consists of programs designed to facilitate the use of the computer by the user. The followings are some characteristics of system software:

Ø  System software exists primarily for the computer itself, to help the computer perform specific functions.

Ø  One major type of system software is the operating system (OS). All computers require an operating system.

Ø  The OS tells the computer how to interact with the user and its own devices.

Example of system software:

Common systems software includes MS DOS, Windows95/98/200/XP, the Macintosh OS, OS/2, and UNIX, LINUX etc.

Application Software:

Ø  Application software is a program designed for specific user application.

Ø  Application software tells the computer how to accomplish tasks the user requires, such as creating a document or editing a graphic image.

Some important kinds of application software are:

1. Word Processing Programs: Microsoft Word, Notepad, WordPad, and WordPerfect etc.

2. Spreadsheet Software: Microsoft Excel, Lotus 1-2-3, and LATEX etc.

3. Database Management Software: Microsoft Access, dBASE etc.

4. Presentation Programs: Microsoft PowerPoint

5. Graphics Programs: Microsoft Paint, Adobe Photoshop, and 3D Studio Max etc.

6. Networking Software: Novell NetWare, Microsoft Windows NT Server, Microsoft Windows 2000, etc.

7. Web Design Tools And Browsers: Microsoft FrontPage, Internet Explorer etc.

8. Entertainment: Windows Media Player, Power DVD etc.

Utility Software:

Utility software gives the user greater control over the computer system through efficient file management. For example, file can be easily prepared, copied, deleted, merged, sorted, and updated by using the appropriate utility programs.

Examples of Utility Software:

1.      Antivirus Software (Norton, McAfee etc.),

2.      File Compression Utilities (Win Zip),

3.      Disk Management Utilities (Disk Defragmenter, Disk Cleanup etc.).

—— ○ ——

23. Describe the structure of FDD and HDD. Calculate the storage capacity of a 3.5” HD/ED/DD floppy disk. Define low-level & high-level formatting.

Ans. to the question no: 23

Structure of Floppy Disk Drive (FDD):

A floppy disk is a thin magnetic-coated disk contained in a flexible or semi-rigid protective jacket. Data is stored in tracks and sectors. The 3½-inch disk is made of two pieces of rigid plastic, with the fabric-medium-fabric sandwich in the middle. The front has only a label and a small aperture for reading and writing data, protected by a spring-loaded metal cover, which is pushed back on entry into the drive.

 

Figure 23.1:The basic internal components of a 3½-inch floppy disk: 1. Write-protect tab, 2. Hub, 3. Shutter, 4. Plastic housing, 5. Paper ring, 6. Magnetic disk, 7. Disk sector.

The 3½-inch floppy disk drive automatically engages when the user inserts a disk, and disengages and ejects with the press of a button, or by motor on the Apple Macintosh.

           

 

Figure 23.2: Floppy disk drive on front of the system case                     Figure 23.3: Inside of a FDD

 

Figure 23.4: Internal Architecture of FDD

The reverse has a similar covered aperture, as well as a hole to allow the spindle to connect into a metal plate glued to the media. Two holes, bottom left and right, indicate the write-protect status and high-density disk correspondingly, a hole meaning protected or high density, and a covered gap meaning write-enabled or low density. (Incidentally, the write-protect and high-density holes on a 3½-inch disk are spaced exactly as far apart as the holes in punched A4 paper (8 cm), allowing write-protected floppies to be clipped into European ring binders.) A notch top right ensures that the disk is inserted correctly, and an arrow top left indicates the direction of insertion. The drive usually has a button that, when pressed, will spring the disk out at varying degrees of force. Some would barely make it out of the disk drive; others would shoot out at a fairly high speed. In a majority of drives, the ejection force is provided by the spring that holds the cover shut, and therefore the ejection speed is dependent on this spring. Data are read from or writtrn onto the disk by a read/write head. This head moves in or out over the head-access slot in the jacket to access different tracks on the surface of the disk.

Structure of Hard Disk Drive (HDD):

The hard disk drive in computer system is the "data center" of the PC. It is here that all of programs and data are stored between the occasions that use the computer. Hard disk (or disks) is the most important of the various types of permanent storage used in PCs (the others being floppy disks and other storage media such as CD-ROMs, tapes, removable drives, etc.) The hard disk differs from the others primarily in three ways: size (usually larger), speed (usually faster) and permanence (usually fixed in the PC and not removable).

Figure 23.5: Internal structure of a HDD

A hard disk uses round, flat disks called platters, coated on both sides with a special media material designed to store information in the form of magnetic patterns. Cutting a hole in the center and stacking them onto a spindle mount the platters. The platters rotate at high speed, driven by a special spindle motor connected to the spindle. Special electromagnetic read/write devices called heads are mounted onto sliders and used to either record information onto the disk or read information from it. The sliders are mounted onto arms, all of which are mechanically connected into a single assembly and positioned over the surface of the disk by a device called an actuator. A logic board controls the activity of the other components and communicates with the rest of the PC.

Each surface of each platter on the disk can hold tens of billions of individual bits of data. These are organized into larger "chunks" for convenience, and to allow for easier and faster access to information. Each platter has two heads, one on the top of the platter and one on the bottom, so a hard disk with three platters (normally) has six surfaces and six total heads. Each platter has its information recorded in concentric circles called tracks. Each track is further broken down into smaller pieces called sectors, each of which holds 512 bytes of information.

Calculation: Storage capacity of a HD (Higher Density) floppy disk which size is 3.5".

We know,

            A 3.5" floppy disk has 80 tracks

            HD floppy disk has 18 sectors

            Each sector contains 512 bytes of data.

Storage capacity is –

= (2×80×18×512) byte

= 1474560 byte = 1440 KB                            [1024 byte = 1 KB]

= 1.40625 MB.                                                [1024 KB = 1 MB]

Storage capacity of ED floppy disk:

            ED floppy disk has 36 sectors

 (2×80×36×512) byte

= 2949120 byte = 2880 KB                            [1024 byte = 1 KB]

= 2.8125 MB. .                                                [1024 KB = 1 MB]

Storage capacity of DD floppy disk:

            ED floppy disk has 9 sectors

 (2×80×9×512) byte

= 737280 byte

= 720 KB.                               [1024 byte = 1 KB]

Ø  Low-level formatting: Sectors (or cluster) are the smallest addressable unit in a hard disk. Marking the tracks and sector is known as low-level formatting. Low-level formatting also creates master boot record (MBR) – a set-aside area for special purpose.

Ø  High-level formatting: A low-level formatted hard disk is required to be partitioned into one or more logical partitions. Each partition can be split into one or more logical drives. Each drive needs to be formatted by an operating system to create file system and FAT (File Allocation Table). This type of formatting is called high-level formatting.

—— ○ ——

24. What is OS? Define various types of OS with their examples. What is the function of OS?

Ans. to the question no: 24

Operating System (OS): An operating system is an organized collection of software that controls the overall operations of a computer. In other words, an operating system is a program that acts as an interface between a user of a computer and computer hardware. The primary goal of an OS is to make the computer system convenient to use. A secondary goal is to use the computer hardware in an efficient manner.

Types of OS: Operating systems can be classified in a number of ways: by how they organize primary memory, by how many different programs they can execute concurrently, by what kind of secondary storage devices they use for work areas, by the setting in which they are to be used, or by the basic design of their components. So, operating system can be classified according to above outstanding, characteristics, but some overlap occurs among the categories. We will divide operating system into four types:

1. Serial Batch-Processing
2. Multiprogramming
3. Time Sharing
4. Multiprocessing

1. Serial Batch-Processing: Batch processing involves collecting transactions together over some interval of time and then processing the whole batch. Serial batch processing operating system can run only a single user program at a time. These are simple systems generally used on mainframes that run in batch mode and on single-user microcomputers. In another words, a system, in which a number of similar items or transactions to be processed are grouped (bathed) for sequential processing during a machine run. For example, suppose the operators received one FORTRAN job, one COBOL job and another FORTRAN job. If they ran them in that order, they would have to set up for FORTRAN (load the compiler tapes), then set up for COBOL and finally set up for FORTRAN again. If they ran the two FORTRAN programs as a batch, however, they could set up only once for FORTRAN, saving operator time. The following diagram shows, how each program is run before the next begins.

 

Figure 24.1: Serial-batch processing operating systems.

Advantages:

Ø  It allows a computer to be dedicated to a specific use.

Ø  It is less complex.

Ø  There is only user at a time.

Ø  There is no possibility that multiple programs will deadlock.

Disadvantages:

Ø  A long turnaround time is needed.

Ø  Batch systems are slow in both processing and output.

Ø  In batch system the programs must be debugged statically.

Examples: CP/M, DOS, and Macintosh operating system are the example of serial batch-processing systems.

2. Multiprogramming Operating System: This system involves simultaneous handling of multiple independent programs by interleaving or overlapping their execution. Multiprogramming operating systems can execute several jobs concurrently by switching the attention of the CPU back and forth among them. This switching is usually prompted by a relatively slow input, output or storage request that can be handled by a buffer, spooler or channel, freeing the CPU to continue processing.

 

 

Figure 24.2: Multiprogramming operating systems

Advantages:

Ø  It increases CPU utilization.

Ø  It decreases total real time needed to execute a job.

Ø  It maximizes the total job throughput (the amount of work accomplished in a given time interval) of a computer.

Disadvantages:

Ø  It is fairly sophisticated and more complex than serial batch processing operating system.

Ø  Multiprogramming operating systems must keep track of all the fobs it is concurrently running.

Examples: UNIX, Pick and IBM VM can be classified as multiprogramming operating system.

3. Time Sharing Operating Systems: Time-sharing operating systems are time driven multiprogramming systems that serve several users concurrently by rapidly switching among them. With time-sharing systems, many users simultaneously share computer resources. Each makes use of a tiny slice of CPU time and then relinquishes the CPU to another uses. As the system switches rapidly from one user to the next, user are given the impression that they each have their own computer. Users are unaware that there are other users on the system. Windows 95, 98, 2000, XP are the time-sharing operating systems.

— — 2 – millisecond time slices of CPU attention   —

JOB A

JOB B

JOB C

JOB D

JOB B

Job B is given higher priority by allowing it two time slices per cycle.

JOB A

One cycle   JOB B

JOB C

JOB D

JOB B

JOB A

JOB B

JOB C

JOB D

JOB B

— — —

Figure 24.3: Time sharing operating systems

4. Multiprocessing Operating Systems: Multiprocessing operating systems can execute several jobs simultaneously through the use of more than one processor. Multiprocessing is the execution of several instruction in parallel fashion on a single computer system having several central processing units. The example of multiprocessing operating systems is SOLRIS.

Multiprocessing systems can be subdivided into four general types, all of which have more than one processor; they are:

1. Homogeneous Multiprocessors
2. Non-homogeneous Multiprocessors
3. Array Processor
4. Pipeline Processors

	Common main storage

 

 

Figure 24.4: Multiprocessing operating system

Advantages:

1. The main advantage of multiprocessing systems is speed; since more than one CPU is available; jobs can be processed faster than they can with only one CPU.
2. Multiprocessing systems are high-performance operating systems, implemented almost exclusively on mainframes and supercomputers.
3. In this system CPU will more likely be available when it is requested.

Function Of OS:

1.      Process Management

2.      Memory Management

3.      Device Management

4.      Storage Management

5.      Application Interface

6.      User Interface

—— ○ ——

25. What are the types of languages? Describe with example.

Ans. to the question no: 25

Types of Languages:

The instruction given to the computer must have a particular format. Computers are unable to understand human language. There are several levels of format or language, which a computer can understand. The interest of understanding computer languages increases day by day. The programming languages are classified in three types:

1. Low-Level Languages

2. High-Level Languages

3. Fourth Generation Languages (Non-Procedural Languages)

There are, however, languages that are high-level in nature but do not serve the purposes of traditional programming. These languages are used for various other purposes. Two common types of such languages are:

1. Scripting Languages

2. Special Purpose Languages

1. Low-Level Languages:

In odd days computers were very large and were not much reliable. Switches did programming and there was no facility to use the program. This approach of computer programming was completely a hardware technology. Next the approach of machine language comes up. In this approach instruction set of the computer consists of some numerical digits. This instruction set is used to build up a program. This code is difficult to understand for human beings. Next assembly language was introduced. In assembly language the numerical codes are replaced by suitable names, which are understandable. This has made programming easier.

Ø  Machine language:

The machine language is written in words comprising of 1s and 0s. Computers execute commands or instructions fed into the memories in machine language. The program is entered through the switches located on the front panel or the operator console. The switches are manually set to correspond to the binary code of each instruction; they are then stored in the program memory. After loading the program, the address of the first instruction is manually loaded into the program counter from the front panel. The program is then executed by pushing on start button. Programming in machine language has the following disadvantages:

Ø  The program must be written entirely in machine language (I.e., with 1s and 0s).

Ø  Manually setting the switches on the front panel, corresponding to each instruction in the program, is a tedious and cumbersome process and likely to introduce many errors.

Ø  Errors detection and correction is tedious and consumers even more time.

Ø  Programs written in machine language for a specific machine cannot be used for another type of machine. Rewriting the same program for another machine is a laborious and time-consuming process.

Ø  Assembly Language:

Programming in assembly language is easier than programming in machine language. The programmer is required to write a source code for each instruction in the program and the assembler translates it to machine languages. The programmer maintains total control of the computer operation. Assembly language offers the greatest degree of efficiency in operation and execution of programs. The followings are the characteristics of assembly language:

Ø  Designed to overcome shortcomings of machine languages

Ø  Create a more productive, user-oriented environment

Ø  Earlier termed second-generation languages

Ø  Now viewed as low-level programming languages

Ø  Use of symbolic operation codes rather than numeric (binary) ones

Ø  Use of symbolic memory addresses rather than numeric (binary) ones

Ø  Pseudo-operations that provide useful user-oriented services such as data generation

2. High-level languages:

These types of languages are like English language. But this is more structured. Actually this type of languages support mathematical notations used in arithmetic expressions. There are some special rules for writing programs in high-level languages. High-level languages are easy to write, compile and suitable for error correction. The followings are some of the high level languages:

Ø  FORTRAN (Formula Translation)

Ø  BASIC (Beginner’s All-purpose Symbolic Instruction Code)

Ø  PASCAL

Ø  C/C++

Ø  Java

3. Fourth Generation Languages (Non-Procedural Languages):

Scientists are trying to develop computer languages like human languages. They have not been successful but may be successful in near future. These languages have greater built-in facility such as database query, searching, sorting and interfacing. FoxPro, Oracle, MATLAB, etc. are some of the fourth generation languages.

—— ○ ——

26. What is network? Why we use network? Illustrate the types of network.

Ans. to the question no: 26

Network:

A Computer Network is an interconnected collection of autonomous computers in order to share information. An autonomous computer is one whose start, stop and control do not depend on any other computer. Or, Network is a group of computers and other devices, such as printers and scanners, connected by a communications link, enabling all the devices to interact with each other.

Two computers are able to exchange information then they are called interconnected. This connection between two computers may be using copper wire, telephone lines, fiber optics, microwaves, and communication satellites.

Networks can be small or large, permanently connected through wires or cables, or temporarily connected through phone lines or wireless transmissions. The largest network is the Internet, which is a worldwide group of networks.

We use Networks for the following reasons:

1. Resource sharing: Programs, equipment, and data available to anyone on the network can be shared without regard to the physical location of resource and the user.

2. High reliability: Alternative sources of resource supply provide high reliability. For example, files could be placed on two or three computers, so if one of them is unavailable due to a hardware failure, the other copies could be used. In addition, for presence of multiple CPUs, if one goes down the other may be able to take over its work.

3. Saving money: Resource sharing provides considerable saving money.

4. Salability: Computer network provides ability to increase system performance gradually as the workload grows just by adding more processor in the network.

5. Communication medium: A computer network provides a powerful communication medium among widely separated people. For example, it is easy for two or more people who live far apart to write a report using a computer network.

6. Simultaneous Access:

Ø  In organizations, many people may need to use the same data or programs. A network solves this problem.

Ø  Shared data and programs can be stored on a central network server.  A server that stores data files may be called a file server.

Ø  Managers may assign access rights to users.  Some users may only be able to read data; others may be able to make changes to existing files.

Figure 1 shows the illustration of simultaneous access.

				This user can open the files; make changes to them, and save the changes on the server. All users see the changes that this user makes to the shared data. This type of access privilege is called “read/write” access.

 

Figure 26.1: Simultaneous Access

7. Shared Peripheral Devices:

Ø  Because peripheral (external) devices like printers can be expensive, it is cost-effective to connect a device to a network so users can share it.

Ø  Through a process called spooling, users can send multiple documents (called print jobs) to a networked printer at the same time. The documents are temporarily stored on the server and printed in turn.

8. Personal Communication:

Ø  One of the most common uses of networks is for electronic mail (e-mail).

Ø  An e-mail system enables users to exchange written messages (often with data files attached) across the local network or over the Internet.

Ø  Two other popular network-based communications systems are teleconferencing and videoconferencing.

Figure 1 shows the illustration of Personal Communication.

 

Figure 26.2: Personal Communication

9. Easier Backup:

Ø  Networks enable users to easily back up (make backup copies of) important data.

Ø  Administrators commonly back up shared data files stored on the server, but may also use the network to back up files on users' PCs.

Types of Computer Networks:

Ø  Types of Computer Networks Based on Transmission Technology:

There are two types of computer networks based on transmission technology:

1. Broadcast Networks: Broadcast networks have a single communication channel that is shared by all the computers on the network. All the others receive packets sent by any computer. An address field within the packet specifies for whom it is intended. Upon receiving a packet, a computer checks the address field. If the packet is intended for some other computer, it is just ignored.

 

Figure 26.3: Broadcast networks.

2. Point-to-point Networks: Point-to-point networks consist of many connections between individual pairs of computers. To go from source to the destination, a packet on this type of network may have to first visit one or more intermediate computers.

 

Figure 26.4: Point-to-point networks.

Ø  Types of Computer Networks Based on Their Scale:

1. Local Area Networks (LAN): Local area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in size. They are widely used to connect personal computers and workstations in company offices and factories to share resources and exchange information. The characteristics of LANs are:

• Its activities are limited in small area.

• The rate of data transfer is usually between 0.1 to 100Mega bits per second.

• The computers are connected in series combination.

• It is easy to establish and cheaper to construct a LAN.

 

Figure 26.5: A very simple LAN (Bus topology)

2. Metropolitan Area Networks (MAN): A metropolitan area network, or MAN, is basically a bigger version of a LAN and normally uses similar technologies. It might cover a group of nearby corporate offices or a city and might be either private or public.

Figure 26.6: Metropolitan Area Network (MAN)

3. Wide Area Networks (WAN): A wide area network, or WAN, spans a large geographical area, often a country or continent. It contains a collection of computers intended for running user programs called hosts or end systems. The hosts are connected by a communication subnet, or just subnet for short. The following benefits are available from WAN:

·         Various statistical data, newspapers, journals, books, movies can be collected and used.

·         Letters can be sent to any place of the world by electronic mail (e-mail) system.

·         Bulletin boards can be formed individually or jointly.

·         Online shopping can be done.

LAN 1

LAN 2

Type A header Payload

Server

Type A header Payload

Significant geographical distance

Type A header Payload

ROUTER

ROUTER

Server

 

Figure 26.7: Wide Area Network (WAN)

Ø  Types of Computer Networks Based on Server:

Ø 

Ø 

Ø 

Ø 

Ø 

In addition to the individual users' PCs (nodes), many networks use a central computer, called a server.

A server has a large hard disk for shared storage.  It may provide other services to the nodes, as well.

In a file server network, nodes can access files on the server, but not necessarily on other nodes. Server-Based Networks are:

1. Client/Server Networks:

Ø  In client/server computing, individual nodes share the processing and storage workload with the server.

Ø   

Ø  Client/server networks require specialized software that enables nodes and the server to collaborate on processing and storage, but no special type of network hardware.

Figure 26.8: Client/Server Network.

2. Peer-to-Peer Networks:

Ø  In a peer-to-peer network, all nodes have an equal relation to one another.

Ø  Each node usually has access to some resources on other nodes, so users can share files, programs, or devices on other users' systems.

Ø  Some peer-to-peer networks use a server, but some do not.

 

	If the user on this node needs a file on another node, the user simply copies the file.		The user on this machine may not even know that the file was copied.

 

Figure 26.9: Peer-to-Peer Networks.

3. Hybrid Networks: Hybrid networks are the combination of both Client/Server and Peer-to-Peer Networks. In a hybrid network, there is one or more server and central control, but individual computers still can share resources among themselves. Hybrid networks benefit from the presence of central control but also inherit the weakness of client-server networks. They enjoy the freedom of peer resource sharing.

Ø  Inter-networks:

Many computer networks exist in the world, often with different hardware and software. People connected to one network often want to communicate with people attached to a different one. This desire requires connecting together different and frequently incompatible networks. The connection is made by using computers called getaways to provide the necessary transition both in terms of hardware and software. A collection of interconnected networks is called an inter-network or just Internet.

A common form of Internet is a collection of LANs connected by a WAN.

The Internet is a specific world wide Internet that is widely used to connect universities, government offices, companies, and private individuals.

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27. What is network topology? Describe all types of network topology with example of each.

Ans. to the question no: 27

The Network Topology: The manner in which computers in a network are geometrically arranged and connected is known as the Network Topology.

There are 6 kinds of network topologies and these are:

1. Bus Topology: In a Bus Topology, all the computes are connected to a common transmission medium. As a result of this, only one pair of computes on the network can communicate at the same time. Each computer has a unique address, which is used when information is transmitted. When a data packet is sent out, it propagates throughout the medium and is received by all computers. To receive message, each computer continuously monitors the medium and copies those messages that are addressed to it as the data packets go by. Since the transmission medium in a bus is generally time-shared, there must ne some type of control mechanism to prevent several stations from transmitting simultaneously.

Figure 27.1: Bus Topology

Ø  Characteristics of Bus Topology:

1. Network maintained by a single cable.
2. Cable segment must end with a terminator.
3. Uses thin coaxial cable (backbones will be thick coaxial cable).
4. Extra stations can be added in a daisy chain manner.
5. Standard is IEEE 802.3
6. Thin Ethernet (10Base2) has a maximum segment length of 200 meter.
7. Maximum number of connections is 30 devices.
8. Four repeaters may be used to a total cable length of 1000 meter.
9. Maximum number of nodes is 150.

10. Thick Ethernet (10Base5) used for backbones.
11. Limited to 500 meter.
12. Maximum of 100 nodes per segment.
13. Total of four repeaters, 2500 meter, with a total of 488 nodes.

Ø  Advantages of Bus Topology:

1. Easy to implement and extend.
2. Well suited for temporary networks that must be set up in a hurry.
3. Typically the least cheap topology to implement.
4. Failure of one station does not affect others.
5. Easy to connect a computer or peripheral to a linear bus.
6. Requires less cable length than a star topology.
7. Easy to add stations.
8. Works well for small networks.

Ø  Disadvantages of Bus Topology:

1. Limited cable length and number of stations.
2. Maintenance costs may be higher in the long run.
3. Performance degrades as additional computers are added.
4. Entire network shuts down if there is a break in the main cable.
5. Terminators are required at both ends of the backbone cable.
6. Difficult to identify the problem if the entire network shuts down.
7. Not meant to be used as a stand-alone solution in a large building.

8. No longer recommended.
9. Limited number of devices can be attached.
10. Sharing same cable slows response rates.

2. Ring Topology: In a ring topology, consecutive computers are connected by point-to-point links, which are arranged to form a single closed path. Data are transmitted from node to node around the ring. The interface at each computer has the ability to recognize packets destined to it.

Figure 27.2: Ring Topology

Ø  Characteristics of Ring Topology:

1. No beginning or end (a ring in fact!)
2. All devices of equality of access to media
3. Single ring – data travels in one direction only, guess what a double ring allows!
4. Each device has to wait its turn to transmit

5.      Most common type is Token Ring (IEEE 802.5)

6. A token contains the data, reaches the destination, data extracted, acknowledgement of receipt sent back to transmitting device, removed, empty token passed on for another device to use

Ø  Advantages of Ring Topology:

1. Growth of system has minimal impact on performance
2. All stations have equal access
3. Data packets travel at great speed
4. No collisions
5. Easier to fault find
6. No terminators required

Ø  Disadvantages of Ring Topology:

1. Most expensive topology
2. Failure of one computer may impact others or a break in the ring will bring it down
3. It is complex to construct
4. Requires more cable than a bus

3. Star Topology: In a star topology, all computers are joined art a single point called the hub.

Figure 27.3: Star Topology

Ø  Characteristics of Star Topology:

1. Like the spokes of a wheel (without the symmetry).
2. Centre point is a Hub.
3. Segments meet at the Hub.
4. Each device needs its own cable to the Hub.
5. Predominant type of topology.

Ø  Advantages of a Star Topology:

1. Easy to install and wire.
2. No disruptions to the network then connecting or removing devices.
3. Easy to detect faults and to remove parts.
4. Can accommodate different wiring.
5. Easy to add devices and new stations as the network expands.
6. One cable failure does not bring down the entire network (resilience).
7. Hub provides centralised management.
8. Easy to find device and cable problems.
9. Can be upgraded to faster speeds.
10. Lots of support as it is the most used.

Ø  Disadvantages of a Star Topology

1. If the hub or concentrator fails, nodes attached are disabled.
2. More expensive than linear bus topologies because of the cost of the concentrators.
3. A star network requires more cable than a ring or bus network.

4. Mesh Topology: Mesh is a highly redundant topology with multiple connections between each node.  The multiple connections allow for more then one way to reach any given node directly.  A true mesh would have a direct connection between every node and every other node.

Figure 27.4: Mesh Topology

Ø  Characteristics of Mesh Topology:

1. Not common on LANs.
2. Most often used in WANs to interconnect LANs.
3. Each node is connected to every other node.
4. Allows communication to continue in the event of a break in any one connection.
5. It is “Fault Tolerant”.

Ø  Advantages of Mesh Topology:

1. Improves Fault Tolerance.

2. Communication can take place directly between any two nodes without an intermediary.

Ø  Disadvantages of Mesh Topology:

1. Expensive.
2. Difficult to install.
3. Difficult to manage.
4. Difficult to troubleshoot.
5.  

5. Tree Topology: A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Figure 27.5: Tree Topology

Ø  Advantages of Tree Topology:

1. Point-to-point wiring in order to individual segments.
2. Supported by several hardware and software venders.

Ø  Disadvantages of Tree Topology

1. The type of cabling used, limits overall length of each segment.
2. If the backbone line breaks, the entire segment goes down.
3. More difficult to configure and wire than other topologies.

6. Wireless Topology: The wireless topology has been developed for mobile computing. In a wireless topology, single or multiple machines can connect through a single wireless access point.

Figure 27.6: Wireless Topology

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28. Describe Computer Virus.

Ans. to the question no: 28

Computer Virus:

Computer Virus is a program that attempts to spread from computer to computer and either cause damage (by erasing or corrupting data) or annoys users (by printing messages or altering what is displayed on the screen). The elaboration of the word VIRUS is Vital Information and Resources Under Siege.

History:

A program called “Elk Cloner” is credited with being the first computer virus to appear “in the wild” -- that is, outside the single computer or lab where it was created. Written in 1982 by Rich Skrenta, it attached itself to the Apple DOS 3.3 operating system and spread by floppy disk.

The Anatomy of A Virus: Basically a virus has three parts:

Ø  Replicator: In order to replicate itself, a virus must be permitted to execute code and write to memory. For this reason, many viruses attach themselves to executable files that may be part of legitimate programs. If a user tries to start an infected program, the virus' code may be executed first. Viruses can be divided into two types, on the basis of their behavior when they get executed. Nonresident viruses immediately search for other hosts that can be infected, infect these targets, and finally transfer control to the application program they infected. Resident viruses do not search for hosts when they are started. Instead, a resident virus loads itself into memory on execution and transfers control to the host program. The virus stays active in the background and infects new hosts when other programs or the operating system itself accesses those files.

Ø  Concealer: Concealer hides the virus from the eyes of users and anti-virus programs. Unless a virus is detected, it cannot be removed. Today’s viruses use advance techniques to camouflage them.

Ø  Payload: The payload of a virus can be practically anything, but generally it refers to the damage a virus causes. Virus opting for long life has no or very little payload so that the users do not notice their existence. Other viruses, however, can format hard disks, delete files, erases operating systems, show annoying messages, reboot computer and even erase the BIOS ROM program.

Types of Viruses:

Ø  Boot Sector Viruses: These viruses infect boot record of a floppy or hard disk. Boot viruses move the boot record program elsewhere and copies them in boot sector. When the computer is started, the virus copies gets loaded into main memory where it can hide and infect other disks. Computer that tries to read an infected floppy disk also gets infected. Example of boot viruses: Form, Disk Killer, PETTER, QRRY and Stone.

Ø  Program Viruses: This type of virus infects executable program files, such as those with extensions like .BIN, .COM, .EXE, .OVL, .DRV and .SYS. When an infected program is run, the virus also gets executed. Example includes Sunday, June 12^th, July 13^th and Cascade

Ø  Stealth Viruses: These viruses reside in memory and use certain techniques to avoid detection. They can also conceal the changes they make. They often befool the operating system and user. Example includes Frodo, Joshi and Whale.

Ø  Polymorphic Viruses: This kind of viruses, uses garbling or encryption technique to mutate themselves so that they appear different in each infection. Those viruses are more difficult to detect. Examples of polymorphic viruses are Involuntary, Stimulate, Cascade, Phoenix, Evil, and Proud etc.

Ø  Macro Viruses: A macro virus is a fragment of code that infects the macros within a specific type of document file, such as MS Word or Excel files. They also infect the templates so that every new document gets infected. Any computer opening an infected Word or Excel file will also fall victim. Example includes DMV, Nuclear, and Word Concept.

Ø  Trojan Horses: A Trojan horse is malicious but benign program that does not replicate when infecting a system but used to open back doors or security holes so that hackers (virus writers) can take control over the infected system or steal vital data. As an example, QAZ helped hackers steal secret source codes at Microsoft web sites.

Ø  Worm: Worms are viruses that have the capability to spread themselves over networks. Worms are commonly spread over the Internet using email attachments. When a user opens an infected email, the worm gets installed on the computer. The virus then collects email address from the address book of mail program, and sends itself to those addresses. The worm Blaster infected more than 1 million computers worldwide in August 2003.

Prevention of Viruses: Computer virus can cause huge loss of data if sufficient measures are not taken. As prevention is better than cure, computer viruses are to be prevented from infecting computers. To stay free from viruses the following steps should be followed:

Ø  Floppies from other users should be avoided. Floppies are hosts of boot virus.

Ø  Any program downloaded from the Internet should not be executed without checking for viruses in them.

Ø  Shareware games are known to be good carrier of viruses. They should be run after virus inspection.

Ø  Worms are spread relying on the ignorance and curiosity of email users. Email from unexpected sources should never be opened or read.

Ø  Script (VB/Java) should be given minimum privileges in Internet browser software. Installing any form of component directly from the Internet should be avoided.

Removing Viruses: Computers infected with viruses are cured with Antivirus programs. The followings are some popular Antivirus software:

1. McAfee Antivirus
2. Norton Antivirus
3. AVG Antivirus
4. PC Cillin Antivirus

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29. Draw a flowchart/Algorithm to sum all odd/even numbers below 20/50.

Ans. to the question no: 29

Flowchart/Algorithm to sum all odd numbers below 20:

1. Start
2. Statement 1
3. Read ODD NUMBER, SUM
4. Statement / operation 2
5. If ODD NUMBER IS LESS THAN 20, go to step 3
6. Print SUM
7. END

 

Flowchart/Algorithm to sum all even numbers below 50:

8. Start
9. Statement 1
10. Read EVEN NUMBER, SUM
11. Statement / operation 2
12. If EVEN NUMBER IS LESS THAN 50, go to step 3
13. Print SUM
14. END

 

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