information technology

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CHAPTER 1 INTRODUCTION TO INFORMATION TECHNOLOGY

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Q No 1: What is Information Technology?

INFORMATION TECHNOLOGY:The use of computers for the storage, processing and communication of information is calledinformation technology. It is the field of management of computers. It is the study of

development and management of computer-based information systems."

Q No 2:

What are different types of data?

TYPES OF DATA:Information can be in one of the following forms:

Data: Information in its basic form is called data. It is not meaningful information.

Text: Information in words and phrases is called text.

Voice: information in spoken words is called voice.

Image: information in the form of pictures, graphs, charts and animation is called image.

Q No 3:

What is microprocessor? What is the role of microprocessor in IT

revolution?

MICROPROCESSORA microprocessor is a small silicon chip installed on motherboard or other processing devices. It

performs all the functions of computer.

Microprocessors have made the world a global village. It has made the work much easier than

before. We have calculators, washing machines, microwave ovens, ATM machines and so many

other electronic devices that are made to perform different jobs easily. We have personal

computers, laptops through which we can connect to the whole world while sitting at our home.

Q No 4:

Define following terms: Hardware, Software and Firmware.

HARDWAREThe physical components of computer are called computer hardware. For example, keyboard,

mouse, monitor hard disk, RAM, CPU and buses, ports etc.

SOFTWAREComputer software is the set of programs that performs some specific tasks.

Software is of two types:

1. System software

2. Application software

FIRMWAREFirmware is a combination of hardware and software. It consists of software fixed in it during

manufacturing. Firmware is used when the programs must not be lost when the power is off.

Typical examples of firmware are calculators, hard disks, mobile phones and digital cameras.





Q No 5:

What is meant by applications package?

APPLICATIONS PACKAGEAn application Package is a collection of programs that perform some particular task. For

example, Word processing application package consists of programs used to prepare textdocuments. MS OFFICE is an application package that contains different programs (like Word,

Excel, PowerPoint etc) for different purposes.

Different application packages are:

1.

Spreadsheet software

2. Word processing software

3.

Business software

4.

Communication software

5.

Games

Q No 6:

What is software? Explain different types of software.

COMPUTER SOFTWAREA computer program is a set of instructions to solve a particular problem. Computer software are

of two types:

1.

System software

2.

Application software.

SYSTEM SOFTWAREThe system software is a set of programs that control the overall working of computer system.

Without system software, it is difficult to work on computer. It helps in running the computer

hardware and the computer system. Different system software include: operating system, device

drivers, language translators, utility programs etc.

APPLICATION SOFTWAREThis is the software that enables us to do the things that we bought our computer for. These are

used to solve user problems. Business software, databases and educational software are some

forms of application software.

Q No 7: Define input and output? List various input and output devices.

INPUT:The data or commands given to computer are called input. Different input devices are mouse,

keyboard, scanner, digital camera, light pen etc.

OUTPUT:

The data after processing is called output. Different output devices are printer, monitor, speaker, plotter.

Q No 8: What is an I/O processor?

I/O PROCESSOR:

Most of the computers have one or more special I/O processors. Input/output operations are





performed by these special processors when the CPU is busy in other difficult computations. The

I/O processors can run in parallel with the CPU.

Q No 9:

What is keyboard used for? How many types of keys are there on thekeyboard? Briefly define each one.

KEYBOARD:

A keyboard is the set of typewriter-like keys that enables you to enter data and instructions into a

computer.

TYPE OF KEYS: Different types of keys on a computer keyboard are:

1. Alphanumeric keypadThese keys consist of all of the letters and numbers on the keyboard. A-Z and 0-9.

2.

Numeric keypad These keys consist of digits 0 to 9 and basic arithmetic operation symbols.

3. Function Keys:These keys consist of 12 function keys F1 to F12. These are used as commands to

various functions.

4. Special keys

There are various special keys on the keyboard. Some of these are:

Alt key: This key is used in combination of other keys to give commands.

Arrow Keys: Most keyboards have four arrow keys that enable you to move the cursor

up, down, right, or left.

Backspace key: Deletes the character just to the left of the cursor and moves the cursor

to that position.

Caps Lock Key: A toggle key that, when activated, causes all alphabetic characters to be

uppercase.

Ctrl key: This key is used in conjunction with other keys to produce commands.

Delete Key: It deletes the character at the current cursor.

Enter Key: It is used to enter commands or to move the cursor to the beginning of the

next line. Sometimes labeled Return instead of Enter.

Esc Key: This key is used to exit from programs and tasks.

Q No 10: Write short note on mouse.

MOUSE:

A mouse is a pointing device. It consists of an object with two buttons. Left button is used to

select or open icons and right button is used to see the properties of icons, folders etc. It

sometimes consists of "wheels", which allow the user to perform operations like scrolling the

page up and down. A cursor represents the position of mouse on the screen. Laser mouse and

wireless mouse are very common.







Q No 16:

What is speech recognition?

SPEECH RECOGNITION

Translating voice into text is called speech recognition. Speech recognition applications includesearch simple data entry, speech-to-text processing etc.

Q No 17: What are major problems in recognition of speech in computers?

PROBLEMS IN SPEECH RECOGNITION

i) There may be inconsistency between the written and spoken words in English.ii)

There may be wide variations between the speech patterns of one individual and

another. So the system has to be 'trained' to recognize the user's particular speech

iii)

Speech-recognition systems have either limited vocabulary or very large vocabulary.Q No 18: Write a short note on video camera.

VIDEO CAMERA

A video camera is used for getting electronic motion picture. Video cameras are used primarily

in two modes. a live broadcast or recorded image sand videos.

These are used for security, military, and industrial operations where secret or remote viewing isrequired. They are also used for producing images and videos that are stored on disk for further

processing.

Q No 19:

What is a scanner?

SCANNER

A scanner is an input device. It is used to scan images on the paper and convert into electronic

form that can be stored in computer memory. These image scan be edited by graphics software

for various purposes.

Q No 20: Define softcopy and hardcopy output.

SOFT COPY

The data displayed on the screen, or saved in some storage device is called softcopy output. Thisoutput can be changed easily. Monitor, speaker, hard disk provide softcopy output.

HARD COPY

The output produced on the paper is called hard copy output. Printers and plotters produce

hardcopy output.





Q No 21:

Define following terms: pixel and resolution.

PIXEL

A pixel (or picture element) is a single point in an image. This is the smallest unit of picture thatcan be controlled.

RESOLUTION

Number of pixels on the display screen to produce images is called resolution. More the number

of pixels, greater will be the resolution.

Q No 22: What is the effect of resolution on the quality of image?

If we increase the resolution, we will get clearer image. High resolution images take more space

in memory than low resolution images.

Q No 23:

What are different screen resolutions available in today’smonitors?

Different types of monitors based on resolution are the followings:

1.

Enhanced Graphics Adaptor (EGA)

2. Video Graphics Array (VGA) with a resolution of 640 by 480.

3.

Extended Graphics Array (XGA) with a resolution of 1024 by 768 pixels

4. Super VGA

Q No 24: Explain different kinds of monitors in detail.

Monitors are of two types based on the technology used.

1. CATHODE RAY TUBES

Most computer monitors arc based on Cathode Ray Tubes (CRTs), similar to those used in TV

sets.

WORKING:

In CRT monitors, a beam of electrons emitted by an electron gun passes through focusing and

deflection systems that direct the beam towards specified points on the phosphor-coated screen.

The phosphor then emits a small spot of light at each point contacted by the electron beam.

Deflection of the electron beam is done with electric field. The beam passes between two pairsof metal plates: one pair vertical, the other pair horizontal. A voltage difference is applied to

each pair of plates according to the amount that the beam is to be deflected in each direction. As

the electron beam passes between each pair of plates, it is bent towards the plate with higher

positive voltage.





Different types of phosphors are available for use in CRT. Lower persistence phosphor requires

higher refresh rate to maintain a picture on the screen without flicker. A phosphor with low

persistence is useful for animation, while high persistence phosphors are better suited for

displaying highly complex, static pictures.

In color screens, there are three guns, one for each color Red, Green and Blue (RGB). These

cause each dot of the screen to generate red, green or blue light. The combination of these three

gives the full color spectrum.

2. FLAT SCREENS

Flat screen are used on battery-operated portable computers, as these consume very little power

In an LCD, the image is formed by so-called liquid crystals. These are long rod-like molecules

which though solid can flow like a liquid.

Each pixel on the screen consists of a microscopic electrode positioned below several of these

molecules. As the output from the computer scans the screen a row at a time, it activates each of

these pixels in turn, switching it on or off. When a pixel is on, the crystals twist in such a way

that they block out the light. When it is off, they let the light through.

Passive matrix display has three screens, colored red, green and blue, which are placed on top of

each other. Below the three screens are the thousands of pixel electrodes, which generate light.

By turning the filters on and off in other combinations, other colors can be obtained. Active

matrix screens are difficult to manufacture and are very expensive. They are available with only

a few top-of-the-range computers.

Q No 25:

How flat screens are more useful than CRTs?

1.

Flat screen LCDs are less in weight than CRTs2.

They are less dangerous to eyes than CRTs

3. They provide better quality than CRTs

4. They are easy to carry than LCDs

Q No 26: Define printers. In what aspects computer printers differ?

PRINTERS

Printers are used to produce hardcopy of computer output, normally data or text and graphics.

They are connected to the parallel port on the computer, called LPT1 (short for Line Printer 1).

The main differences between the printers depend on:

1.

The quality of output

2. The ability to print graphics

3.

The printing speed





Q No 27:

Explain different kinds of printers.

PRINTERS

Different kinds of printers are the followings:

IMPACT PRINTERS

The printers that use some physical things like hammer or pins to strike on paper for printing are

called impact printers. Followings are some impact printers:

CHARACTER PRINTERS

Character printers print one character at a time and hence they are slow printers. They arecapable of printing at the rate of 30 to 300 characters per second. The advantage of character

printer is that they are low cost. The disadvantage is low speed and lot of noise while printing.

Character printers are of two types, dot matrix and daisy wheel printers.

DOT MATRIX PRINTERS

Dot matrix has 9 or 24 pins arranged in the form of a matrix. To print a character on the paper,

the built-in microprocessor activates the appropriate pins in the print head to move forward and

hit the ribbon which is placed against a paper. As a result, the shape of the character appears on

the paper. They are low quality printers.

DAISY WHEEL

The print head of a daisy wheel printer is a circular wheel with arms or spokes. The character

shapes are embossed at the outer end of the arms.

To print a character, the daisy wheel rotates so that the required character is positioned in front

of the printer ribbon. Now the spoke containing the required character is hit by a hammer and

strikes the ribbon leaving an impression on the paper placed behind the ribbon. Movement of all

these parts is controlled by microprocessor in the printer. The main advantage of using a daisy

wheel printer is that the print quality is high because exact shape of the character hits the ribbon

to leave an impression on paper.

LINE PRINTERS

Line printers print one complete line a time and hence they are faster than character printers.

Line printers are heavy-duty printers and they can print at the rate of 2000 lines per minute.

1.

CHAIN PRINTER

In Chain printer, print characters are contained in a chain which moves continuously at a rapidrate. Circuits within the printer senses when the correct character appears at the desired print

position on the page. At that point, a hammer strikes the page. This action presses the paper

against a ribbon and against the character located at that position. The result leaves an

impression of that character. As the chain continues to move transversely across the page,





additional characters are printed.

2. DRUM PRINTER

The principal of the drum printer is very similar to that of the chain printer. All the characters in

the specified character set are engraved along circumference of the drum and if 132 print positions are available, this is repeated for each column.

NON-IMPACT PRINTERS

The printers that use do not use physical things to print but use some technology like laser for

printing are called non-impact printers. Non impact printers are Laser and Ink Jet printers.

LASER PRINTERS

Laser printers are page printers, meaning that they print an entire page at a time. They are very

fast, typical speeds being around 8 pages per minute and virtually silent in operation. The print

quality is good, almost equal to that of daisy wheel printers. The resolution of current models is600dpi to 1400 dpi.

WORKING

A sheet of paper is fed from a tray into the machine and receives an electrostatic charge acrossits surface. The laser beam then traces the computer's output as a pattern of tiny dots on the

paper; during this process it removes the electrostatic charge from the points where the beam

strikes the paper. The paper then receives a tine toner across its surface which adheres to the

points with no charge but which is washed off the rest. After passing between rollers, the paper

is heated and dried at the front of machine.

INK JET PRINTERS

An inkjet printer produces hard copy by spraying ink onto paper. A typical inkjet printer can

produce copy with a resolution of at least 300-600dpi.

In the inkjet printing mechanism, the print head has several tiny nozzles. As the paper moves

past the print head, the nozzles spray ink onto it, forming the characters and images. An inkjet

printer can produce from 100 to several hundred pages before the ink cartridges must be

replaced. There is usually one black ink cartridge and one color cartridge containing ink in

primary colors (cyan, magenta, and yellow). Inkjet printers are inexpensive.

Q No 28: Name some impact and non-impact printers.

IMPACT PRINTERS:

1. Dot-matrix printer2.

Daisy wheel Printer

3.

Line printers





NON-IMPACT PRINTER:

1. Laser printer

2. Ink jet printer

Q No 29: How impact printers differ from non-impact printers?

Some differences between impact and non-impact printers are:

1.

Impact printers are noisy but non-impact printers are not noisy

2.

Impact printers are slow but non-impact printers are fast

3.

Impact printers have low quality but non-impact printers have high quality

Q No 30: How dot matrix printer works?

WORKING OF DOT MATRIX PRINTER

Dot matrix has 9 or 24 pins arranged in the form of a matrix. To print a character on the paper,the built-in microprocessor activates the appropriate pins in the print head to move forward and

hit the ribbon which is placed against a paper. As a result, the shape of the character appears on

the paper. They are low quality printers.

Q No 31: What is plotter used for? Discuss the use of different types of

plotters.

PLOTTERS

A plotter is an output device used to produce hardcopy. Plotters are used for a variety ofapplications, which include drawing graphs, making maps, civil engineering drawings and

machine components.

FLATBED PLOTTER

Flatbed plotter is less expensive and is used in many smaller computing systems. It plots on paper that is spread and fixed over a rectangular flatbed. Pens of different colors are mounted in

the pen holding mechanism that moves on the surface in two orthogonal directions. The pen can

be raised or lowered onto the paper during the drawing operations.

DRUM PLOTTER

Drum plotters are normally used with mainframe and minicomputer systems. The paper on

which the design has to be made is placed over a drum that rotates back and forth to produce

vertical motion. The pen is mounted on a carriage which moves across the width of the paper.

The vertical movement of paper and the horizontal movement of the pen create required design.





Q No 32: Define following terms related to computer memory. Memory cell,

memory word, byte, memory capacity, memory address.

MEMORY

The memory in computer is used to store data.

MEMORY CELL

A memory cell consists of a single bit either 0 or 1.

MEMORY WORD

The number of bits that a computer uses to process information is called word. Word size varies

in different type of computers.

MEMORY CAPACITY

Number of words that a computer memory can store is called memory capacity. For example, if

a memory can store 64 words and word size is 8 bits, then memory capacity is 64 x 8 bits.

MEMORY ADDRESS:

A number that tells the location of a word in memory is called address. It is identified by a binary number.

Q No 33:

Write the relationship between memory units.

MEMORY UNITS

Different memory units are:

1 byte = 8 bits

1 KB = 1024 Bytes

1 MB = 1024 KB = 220

Bytes

1 GB = 1024 MB = 230

bytes

Q No 34:

Define read and write operation of memory.

READ OPERATION

The operation in which a memory word is read from memory is called read operation.





WRITE OPERATION

The operation in which a new word is written in a memory address is called write operation.

Q No 35: Define access and cycle time of memory.

ACCESS TIME

The time required to perform a read operation is called access time.

CYCLE TIME

The time required to perform a read or write operation and then return to its original state for

next operation.

Q No 36: What is RWM?

RWM (Read/Write Memory)The memory in which we can read and write data is called read/write memory. For example,

RAM, hard disk etc.

Q No 37: Define static and dynamic memory devices.

STATIC MEMORY DEVICES:The memory device in which the stored data will remain permanently stored as long as power is

supplied is called static memory devices. Memory does not need refresh process to store data.

For example, SRAM.

DYNAMIC MEMORY DEVICES:The memory device in which the stored data will not remain permanently stored even if power is

supplied is called static memory devices. Memory needs refresh process to store data. For

example, DRAM.

Q No 38: Construct general memory diagram of 32 x 4 and 64 x 6 memory.





Q No 39: Explain information system development cycle (system

development life cycle).

INFORMATION SYSTEM DEVELOPMENTThe information system development is a process of planning, creating, testing, and installing aninformation system. Software development is a complex process. It needs variety of steps to

develop a quality system. Information system development can be divided into following phases

as given below.

SYSTEM ANALYSIS:In this stage, the analyst understands the functions of the software which is required for the

system. The analyst makes a brief survey of the requirements and tries to analyze the

performance of the system which is to be developed. He also makes sure that he gets enough

information and resources for building the appropriate system.

SYSTEM DESIGN:

In this stage, the analyst makes number of designs of the system on paper or on the computer.Once this is done, the analyst selects and finalizes a best suited design for the development of the

system.

In this phase, specifications are converted into algorithms and detailed charts that define the data

required and express the processing to be carried out on data.

SYSTEM DEVELOPMENT: This stage deals with actual development of programs using programming languages. We write

and test computer software and develop data input and output forms.

SYSTEM IMPLEMENTATION:

When the system is developed and tested by the software team, it is installed in the user

environment. Users are provided training to use the system. User uses the system and finds bugs

in the systemSYSTEM MAINTENANCE:

If refers to the necessary changes to be made in the system that result from changing

requirements, technologies and experience with system's use.



CHAPTER 2 COMPUTER NETWORKS


Question & Answer

Q No 1:

Define Computer Network. What components comprise a network?

COMPUTER NETWORK:A computer network is a physical connection of two or more computers through some medium

so that they can share information and other resources like printer, disk drives etc.

A network comprises of network hardware like Network Card, Hub, Router, Cables, etc andnetwork software like Network Operating System (WIN XP).

Q No 2: Give some examples of Computer Networks?

EXAMPLES OF COMPUTER NETWORKS:Some examples of computer networks are:

1. A network of Computers in office

2.

A network of computers of different branches of bank3. Internet

Q No 3:

What is the role of computers in a network?

ROLE OF COMPUTERS IN NETWORK:A computer may have one of the two roles in a network: Client Computer or Server Computer.

A Client computer is the one that requests for information or resources from other computers. A

Sever computer is the one that that shares information and resources for client computers.For example, a computer in a network that shares a printer acts as server computer and all other

computers that use that printer are called client computers.

Q No 4:

Explain different types of network models.Based on the role of computers in a network, there are two network models: Client-Server Network (Dedicated Server) and Peer-to-Peer Network.

CLIENT-SERVER (DEDICATED SERVER) NETWORK:A type of network in which one or more computers act as server while all other computers act asclient computers is called client-server network. Server computer is also called host computer.

Server computer controls access to computer software and hardware on the network and

provides centralized storage area for programs and information. Server computers have powerful

processors and large memory capacity. A network administrator controls the entire network. He

grants permissions to different users for using different resources of the computer.Some servers also work as dedicated servers. A dedicated server performs specific tasks. For

example, File Server is used to store and manage files. Print server is used to manage printersand print jobs.

Client computers request resources from the server computer. These computers have slow

processors and less storage as compared to server computers.





ADVANTAGES:

Client-server networks have following advantages:

1.

Centralized - Resources and data security are controlled through the server.

2. Scalability - Any or all elements can be replaced individually as needs increase.

3. Flexibility - New technology can be easily integrated into system.

4. Interoperability - All components (client/network/server) work together.

5. Accessibility - Server can be accessed remotely and across multiple platforms.

DISADVANTAGES:

Client-server networks have following disadvantages:

1. Expense - Requires initial investment in dedicated server.

2. Maintenance - Large networks will require a staff to ensure efficient operation.

3. Dependence - When server goes down, operations will cease across the network.

PEER-TO-PEER NETWORK:A type of network in which each computer is capable of using as well as sharing the resources is

called peer-to-peer network.

Each peer computer stores files on its own storage devices. The network operating system and

application software are installed on each of the peer computer. Each computer may work asclient (when it uses resources of other computers) and server (when it shares resources for

others). There is no central administrator to control the network.

ADVANTAGES:

Peer-to-peer networks have following advantages:

1. It is suitable for small networks.

2. It has less initial expense as there is no need for a dedicated server.

3. It is easy to setup and maintain

DISADVANTAGES:

The major disadvantages of this model are as follows:

1. It is slow network

2. It provides less security





3. It needs more storage

Q No 5:

Differentiate between dedicated server networks and peer-to-peer

networks.

Major differences between dedicated server networks and peer-to-peer networks

are as follows:

CLIENT-SERVER NETWORK PEER-TO-PEER NETWORK

1. Central storage for software and data1. No central storage for software and

data

2. Much secure networks 2. Less secure networks

3. Each computer has specific role 3. No specific role of computers

4. Administrator controls entire

network4. No administrator

5. Used for large networks5. Used for small networks

Q No 6:

Why it is required to have a dedicated server network?

A dedicated server network may be established when following conditions may meet.

1.

Security is the major issue.

2. There is a need to restrict users that they may not use all services.

3. More budgets are available.

4. When number of computers are high

5. When fast processing is needed

Q No 7: When it is required to have a peer-to-peer network?

A peer-to-peer may be established when following conditions may meet.

1. Security is not a major issue.

2. Fewer budgets are available.

3. Network is small.

4. No fast processing needed





Q No 8:

What is network software?

NETWORK SOFTWARE: Network Software is a set of programs that is used to connect and communicate computers and

share information. Normally, no special program is needed as the functionality is provided by the Network operating system like Windows, UNIX, Novell and the Modem/Router driver.

Q No 9:

Describe three benefits of networks.Different advantages of using networks are:

1. Networks allow users to share information.

2. Many computer resources, such as printers or hard drives, can be shared among users.

3. Users can share application program by placing them on server computer.4. There are software which are costly and take time for installation. Computer networks

allow software to be stored or installed on server and can be used by the different

workstations.

Q No 10:

Describe three purposes of networks.

PURPOSE OF NETWORKSA network may be used for the following purposes:

1. We can share data files in a shared location2.

Sharing printers is a primary use of networks.

3. We can place applications on a server. Users then load and run the application over the

network.

4. We can use computer networks for remote working.

Q No 11:

Explain Local area and wide area networks.Based on the physical organization and distance covered, networks can be categorized into

following types:

1. Local Area Network (LAN)2. Wide Area Network (WAN)

3. Metropolitan Area Network (MAN)

LOCAL AREA NETWORK (LAN)A type of network in a small area of building or office is called local area network. The basic

purpose of LANs is to share resources like printers, software and storage.

There may be tens to hundreds of computers connected together in LANs. LANs are generally

found in offices, industries, or educational campuses. The network may be client-server or peer-to-peer as needed by the organization.

LANs provide transmission of data at a very high speed at 1 Mbps to 100Mbps. This

transmission rate is much higher than transmitting data over telephone lines. However, numberof computers attached to a LAN is limited.

WIDE AREA NETWORK (WAN)A type of network that connects many LANs to covers large geographical area is called wide





area network. Millions of computers across the world are connected to this network. WANsoften use telephone lines for data transmission. They can also use satellite. Data transmission

speed is very low at about 56kbps to 45Mbps.

Internet is an example of WAN. Any computer can connect or disconnect to such type of

network so connection is WAN is not permanent. WANs have higher possibility of datatransmission error. Major use of WANs is to share data like email, file transfer, teleconferencing

etc.

Q No 12:

Differentiate between LAN and WAN.

The differences between LAN and Wan are as follows:

LAN WAN

1. It covers small distance 1. It covers large area

2. Transmission speed is very fast up to100Mbps

2. Transmission speed is from 56kbps to45Mbps

3. It is less costly 3. It is expensive

4. The connection in LAN is permanent 4. The connection in Wan is temporary

5. Less possibility of transmission error

6. It is easy to expand

7. Ethernet is common protocol used in LAN

5. Higher possibility of transmission error

6. It is difficult to expand.

7. X.25, MPLS, ATM are common protocols

Q No 13:

Define workgroup and groupware.

WORKGROUP:A workgroup is a group of persons working together on some common project by usingcomputer network. Workgroups provide easy sharing of files, printers and other network

resources.

GROUPWARE:Groupware are the programs that help in workgroup computing. Groupware services can include

collective writing, e-mail handling, shared database access, electronic meetings with each personable to see and display information to others. Some product examples of groupware includeMicrosoft Exchange, email programs, Skype and Microsoft NetMeeting.

Q No 14: What is network topology? Explain its types.

NETWORK TOPOLOGY:

The physical arrangement of computers and other hardware in the network is called network





topology. Different network topologies are as follows:

1. Bus Topology

2.

Star Topology

3. Ring Topology

BUS TOPOLOGY:

In bus topology, all computers are connected to a central cable, called the bus or backbone. The

sending node broadcasts the data to the entire network. The various nodes hear it and look to see

if the data is for them. If so, they keep the data. If not they ignore the data.

ADVANTAGES:

1. It is cheap to establish bus network.

2. It is less costly as compared to star network

DISADVANTAGES:

1. If bus cable breaks, network fails

2. If anyone computer is not working, whole network fails

STAR TOPOLOGY:

In Star Topology, all computers are connected to a central hub. Data on a star network passes

through the hub before continuing to its destination. The hub manages and controls all functionsof the network. It also acts as a repeater for the data flow.

ADVANTAGES:

1. It is easy to install more computers in the network.

2. If a computer is not working, it will not disturb whole network. This is why star topology

is the most common physical topology in Ethernet LANs.

DISADVANTAGES:

1. It is more costly than bus network

2. If hub is not working, whole network will go down.

RING TOPOLOGY:

In a ring topology, computers are cabled together with the last device connected to the first to

form a circle, or ring. It includes both single-ring and dual-ring topologies. In a single-ringtopology, all the devices on the network share a single cable, and the data travels in one direction

only. The dual-ring topology has two rings with two cables, which allows data to send in both





directions. If one ring fails, data can be transmitted on the other ring.

DISADVANTAGES:

1.

Adding or removing computer is difficult.

2. If any of the computers is not working, whole network will go down.

Q No 15: When a bus network breaks down?

A bus network breaks down if:

1. Bus cable breaks

2. Any computer in the whole network is not working.

Q No 16: Differentiate between bus and star topology.

The differences between bus and star network are the followings:

BUS TOPOLOGY STAR TOPOLOGY

1. All computer are connected to central cablecalled bus

All computers are connected to centraldevice called hub

2. If bus cable breaks, network fails If hub is out of order, network fails

3. If anyone computer is not working, wholenetwork fails

Network does not fail by the failure ofsingle computer.

4. It is cheap network It is costly as compared to bus network

Q No 17:

When a ring network breaks down?

A ring network breaks down if:

1. Cable connecting all computers damages at any point

2. Any computer is not working in the network

Q No 18: You need to have a network in your computer lab having 20 PCs.

Which topology would you use and why?

If we need a network in the lab, we will use Star topology. The reason is that it is easy to installand manage. It cost less and network is not disturbed if any computer goes down.

Q No 19:

What is hub?

HUB:

A hub is used in a wired network to connect network cables from a number of devices together.





The hub allows each device to talk to the others. Hubs require no configuration to setup.

Q No 20:

What is ISO?

ISO

ISO (International Organization for Standardization) is the world’s largest developer ofInternational Standards. International Standards give state of the art specifications for products,

services and good practice, helping to make industry more efficient and effective

Q No 21: Explain different layers of OSI model.

OSI MODEL:

Open Systems Interconnection (OSI) model is a reference model developed by ISO(International Organization for Standardization) in 1984. It is a conceptual framework ofstandards for communication in the network.

The OSI model defines the communication process into 7 layers, which divides the tasksinvolved with moving information between networked computers. Each layer has specific tasks.

The functions of each layer are discussed below.

PHYSICAL LAYER

This layer provides the hardware means of sending and receiving data on a carrier, includingdefining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with

physical layer components.

DATA LINK LAYER

At this layer, data packets are encoded and decoded into bits. It provides transmission protocolknowledge and management, handles errors and frame synchronization in the physical layer and

flow control.

The data link layer is divided into two sub layers: The Media Access Control (MAC) layer andthe Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the

network gains access to the data and permission to transmit it. The LLC layer controls framesynchronization, flow control and error checking.

NETWORK LAYERThis layer determines how data are transferred between network devices. It routes packets

according to unique network device addresses. Routing and forwarding are functions of thislayer, as well as addressing, error handling and packet sequencing.

TRANSPORT LAYER

This layer provides clear transfer of data between end systems and is responsible for end-to-end





error recovery and flow control. It ensures complete data transfer. It provides reliable andsequential packet delivery through error recovery and flow control mechanisms.

SESSION LAYER

This layer establishes, manages and terminates connections between applications. The session

layer manages user sessions, terminates conversations and dialogues between the applications ateach end. It controls establishment and termination of logic links between users.

PRESENTATION LAYER

This layer masks the differences of data formats between dissimilar systems. It encodes anddecodes data; encrypts and decrypts data to be sent across a network, compresses anddecompresses data.

APPLICATION LAYER:

This layer supports applications and end-user processes. This layer provides application servicesfor file transfers, e-mail, and other network software services. Telnet and FTP are applications

that exist entirely in the application level.

Q No 22:

In which layers of OSI model, TCP/IP protocol is used?

TCP/IP protocol is used in Network and Transport layer of OSI model.

Q No 23: What is protocol? What are its key elements?

PROTOCOL:

A protocol can be defined as a set of rules that controls and manages data communication. The

key elements of protocol are syntax, semantics and timing.

SYNTAX:

Syntax relates to the format of the data. For example, a simple protocol may expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of receiver, and the

rest of the stream to be the message itself.

SEMANTICS:

Semantics relates to the meaning of each section of bits. How a specified pattern to beinterpreted; and what action is to be taken based on that interpretation? For example, does an

address identify the route to be taken or the final destination of the message?

TIMING:

Timing refers to two vital characteristics: when data should be sent and how fast they could besent. For example if a sender produces data at 100 Mbps but the receiver can process data at only





1 Mbps, the transmission will overload the receiver and data will be largely lost.

Q No 24:

What is IEEE?

IEEE

IEEE Stands for the "Institute of Electrical and Electronics Engineers." This is a non-profitorganization that develops, defines, and reviews electronics and computer science standards. It is

designed to serve professionals involved in all aspects of the electrical, electronic and computing

fields and related areas of science and technology that underlie modern civilization.

Q No 25:

What is TCP/IP?

TCP/IP PROTOCOL

TCP/IP protocol was developed by a Department of Defense (DOD) research project to connecta number different networks designed by different vendors into the Internet.

TCP is responsible for verifying the correct delivery of data from client to server. Data can be

lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger

retransmission until the data is correctly and completely received.

IP is responsible for moving packet of data from node to node. IP forwards each packet basedon the IP address.

Q No 26: What is X.25 protocol?

X.25

X.25 is a standard suite of protocols used for packet switching across computer networks. The

X.25 protocols works at the physical, data link, and network layers of the OSI model.

Each X.25 packets contains up to 128 bytes of data. The X.25 network handles packet assemblyat the source device, delivery, and then disassembly at the destination. X.25 supports multiple

simultaneous conversations by multiplexing packets and using virtual communication channels.Typical applications of X.25 today include ATM networks and credit card verification networks.

Q No 27: Explain circuit switching and packet switching in data

communication.

PACKET SWITCHING

In packet-based networks, the message gets broken into small data packets. These packets aresent out from the computer and they travel around the network seeking out the most efficient

route to travel.

Each packet is sent with a ‘header address’ which tells it where its final destination is. The







Disadvantages

1. It is inefficient because the equipment may be unused for a lot of the call; the dedicatedline still remains open.

2. It takes long time to set up the circuit.

3. It was primarily developed for voice traffic rather than data traffic.



CHAPTER 3 DATA COMMUNICATION


Question & Answers

Q No 1: What is Data Communication?

COMPUTER NETWORK:

Data communication is the process of transferring information from one computer to anotherusing communication media.

Q No 2:

Describe Basic Elements of Data Communication

BASIC ELEMENTS OF DATA COMMUNICATION:

Basic elements of data communication are as follows:

Sender: The system that sends information is called sender.

Receiver: The system that receives information is called receiver.

Medium: The way through which data transmission takes place is called medium

Message: The information being transmitted is called message.

Q No 3:

Explain Data Communication Modes

COMMUNICATION MODES

The way in which communication take place between two devices is called communication

modes. Different communication modes are: simplex, half-duplex and full-duplex connections.

SIMPLEX MODE:

In simplex mode, data flows in only one direction, from the sender to the receiver. This type ofconnection is useful if the data do not need to flow in both directions. In this transmission, it not

sure that data is received at other end or not. Radio and television broadcasting are examples ofsimplex transmission.

HALF-DUPLEX MODE:In half-duplex mode, data flows in both directions, but not both at the same time. This type ofconnection makes it possible to have bidirectional communications using the full capacity of theline. For example, email programs or walkie-talkie system is an example of half-duplex mode.

FULL-DUPLEX MODE:

A full-duplex connection is a connection in which the data flow in both directions simultaneously.





Each end of the line can transmit and receive at the same time. Telephone networks are anexample of full duplex transmission.

Q No 4: Give an example of each simplex, half-duplex and full-duplex mode

of communication.

EXAMPLE OF SIMPLEX MODE:

Transfer of data from computer to printer is an example of simplex mode.

EXAMPLE OF HALF-DUPLEX MODE:

Transfer of data using walkie-talkie is an example of half-duplex mode.

EXAMPLE OF FULL-DUPLEX MODE:

Transfer of data using telephone lines is an example of full duplex mode.

Q No 5:

What is meant by modulation? Explain how data can be transmitted

over telephone lines using amplitude, frequency and phase modulation.

MODULATION:

The process of converting analog signals into digital signals by varying the amplitude, frequencyor phase of signals is called modulation.

1 Amplitude modulation

In amplitude modulation, two different voltage levels are used, for 0 and 1. High voltage level

represents 1 and low voltage level represents 0. A person listening to digital data transmitted at a

very low data rate would hear a loud noise for a 1 and no noise for a 0.

2 Frequency Modulation

In frequency modulation, the voltage level is constant but the carrier frequency is different for 1and 0. A person listening to frequency modulated digital data would hear two tones,corresponding to 0 and 1. Frequency modulation is often referred to as frequency shift keying.

3 Phase Modulation

In simple phase modulation, the amplitude and frequency do not change but the phase of thecarrier is reversed 180 degrees when the data switches from 0 to 1 or 1 to 0.





Q No 6:

What is modem used for?

MODEM:

A modem is a device that converts analog signals into digital and digital signals into analogsignals is called modem.

Q No 7:

Define baud.

Baud:The number of bits transmitted per second through a medium is called baud. It is the unit of

measuring data communication speed.

Q No 8:

What is asynchronous and synchronous data transmission? Explain

how data is transmitted asynchronously and synchronously with

examples.

ASYNCHRONOUS TRANSMISSIONS

In asynchronous transmission, data is sent character by character. The time interval between twocharacters is not fixed, For example, a person typing through keyboard will not type at same

speed, so the time interval between two characters will not be constant.

In asynchronous transmission, there is no way to decide between no data and a 0 bit. A characterconsisting entirely of 0s would be completely invisible. Furthermore, a character consisting of a 1followed by seven 0s could not be distinguished from a character consisting of 7 0s followed by a

1.

In order to recognize the start of a character, a start bit and 1 or 2 stop bits are sent with eachcharacter. Between the start and stop bits, the data bits are transmitted. The most common bit

rates used for asynchronous transmission are 110, 300, 600, 1200 and 2400 bps.

SYNCHRONOUS TRANSMISSIONS

In synchronous transmission, data is sent in the form of packet so there is no need for start andstop bits. So, data transmission becomes fast. . In synchronous transmission, the interval between

two characters is always exactly the same. Synchronous communication often proceeds at bitrates of 4800 bps, 9600 bps or even higher. A special "idle" character is sent when there is no

data.

Q No 9:

Differentiate between synchronous and asynchronous transmission

ASYNCHRONOUS TRANSMISSION SYNCHRONOUS TRANSMISSION

Data is sent character by character Data is sent in packets

Time interval between two characters is not Time interval between characters is fixed





fixed

Start and stop bits are sent with actualcharacter

No need to send start and stop bit

It is slow transmission It is fast transmission

Q No 10:

Define communication media. Explain different media used for data

transmission.

COMMUNICATION MEDIA

Data is transmitted from one device to other through a communication media. Thecommunication media includes the following types:

1. Standard telephone lines

2.

Coaxial cables

3. Microwave transmission

4. Satellite Communications

5. Fiber optics

Telephone Lines

Standard telephone lines are widely used as communication lines. Telephone lines are useful tothe user of data communication. They permit data to be transmitted to almost any location in the

world. These are slow communication lines.

Coaxial Cable

A coaxial cable can transmit information at much higher rate of 10 Mbps. It is mostly used forlong distance transmission. They are also used by telephone companies to transmit data over long

distance. They provide high quality data transmission without distortion or loss of signal. Coaxial

cables have been laid under the ground or under the ocean. Both telephone lines and coaxialcables are usually made up of copper.

Microwave Transmission

Microwave transmission signals travel through open space. They provide a much fastertransmission rate than is possible with either telephone lines or coaxial cables. Microwavesystems transmit information with transmitters which are normally installed on high buildings,mountains tops or high towers. Long distance microwave channels consist of a series of stations

(boosters) spaced approximately 30 miles apart. Two stations must be within sight of one another.





Communication Satellites

Satellite communication is ideal for long distance communication. Earth stations consisting of

ground antennas beam signals to the satellite. The satellite amplifies and retransmits the signals toanother earth station which can be located many thousands of miles away. Transmission by

satellite allows large amount of data to be sent long distance at rapid speeds. However, a majordrawback of satellite communication has been the high cost of placing the satellite into its orbits.

Fiber Optics

Fiber optics is new technology that may replace conventional wire and cable in communicationsystems. The major advantage of fiber optics is less weight and size and fast speed. A single fiberoptic cable can carry up to 50.000 channels.

In fiber optics communication, the transmitter side has a converter that converts electrical signals

into light waves and these are transmitted over the fiber optics. Another converter is placed at thereceiving end that converts the light waves back to electrical signals. Fiber optics provides high

quality transmission at very high speed. Fiber optic transmission is not affected byelectromagnetic interference.

Q No 11: How data is transmitted using fiber optic cables?

In fiber optics communication, the transmitter side has a converter that converts electrical signalsinto light waves and these are transmitted over the fiber optics. Another converter is placed at the

receiving end that converts the light waves back to electrical signals. Fiber optics provides high

quality transmission at very high speed. Fiber optic transmission is not affected by

electromagnetic interference.

Q No 12: What are the advantages of using fiber optic cable?

Fiber optic cables have the following advantages:

1. They provide high data transmission.

2. It is not affected by electromagnetic interference.

3. They can transmit analog and digital data

Q No 13: Define data communication speed, explain how it is measured and

briefly explain narrow band, voice band and broadband.

COMMUNICATION SPEED

Bandwidth describes the data communication capacity of a communication system. More the bandwidth of a communication system, the more it can transmit per second. The grades of





channels are commonly classified into three categories.

Low Speed or Narrow Band

Low speed or narrow band has a bit transmission rate of 40 to 300 baud. In this categorytelegraph communication lines are included. These channels are usually used for low-speed

teletypewriter communications and for other low-speed terminals.

Medium Speed or Voice Band

Medium speed lines operate at rates varying from 300 baud to 56,000 baud. The most commonlyused media for this speed is telephone line. Common speeds include 600, 1200, 2400, 4800, 9600,

14400, 28,800 and 56.000 baud.

High Speed or Broadband

High-speed communication channels, commonly called broadband permit transmissionrates over 56000 baud. High speed channels require microwave, fiber optics or satellite

transmission. They are normally used for computer-to-computer communication. Broadband isused when a large volume of data is to be transmitted at high speed.



CHAPTER 4 APPLICATIONS OF COMPUTERS


Q No 1:

How computers can help in education?

USES OF COMPUTERS IN EDUCATION

Different uses of computers in education field are:

EASE OF LEARNING PROCESS:

Computers are being used in educational institutes to improve the learning process. Teachers canuse audio video aids to prepare lesson plans. They can use it to prepare electronic presentations

about their lectures.

CBT (COMPUTER-BASED TRAINING)

In CBT, we prepare different educational programs with the help of professional teachers andaudio visual aids. These educational programs are generally in the shape of lectures on a specific

subject. These programs are provided on CDs.

ONLINE EDUCATION

Many web sites provide online education. You can read or download educational material and books. For example, Virtual University of Pakistan is an Online Educational Institution. The

students log in to their accounts and e-mail boxes. They interact with different teachers online.

They receive and submit their assignments and work through internet to their teachers.

RESEARCH

Computers are also used for research work. Internet is a huge source of information on any topic.Different researchers can share their research work using Internet.

INSTITUTE ADMINISTRATION

Computers are being used to perform many tasks in educational institutions like:

1. Keeping Records of students

2. Storing Records of employees

3. Managing Accounts of the institution

4. Fees collection and maintenance

5. Circulation of instruction/notices

6. Preparation of school/ college magazine





Q No 2:

What is word processing?

WORD PROCESSING

A word processor is a computer application used for the production including composition,editing, formatting, and printing of any sort of text documents.

The great advantage of word processing is that you can make changes without retyping the entiredocument. If you want to delete a paragraph, you simply remove it, without leaving a trace. It is

equally easy to insert a word, sentence, or paragraph in the middle of a document. Word

processors also make it easy to move sections of text from one place to another within adocument, or between documents. When you have made all the changes you want, you can send

the file to a printer to get a hardcopy.

Microsoft Word is the most widely used word processing software. Microsoft estimates that over500,000,000 people use MS Word.

Q No 3:

What is UPC?

UPC

The Universal Product Code (UPC) is a barcode present on product items that contain differentinformation about that item. A barcode reader is used to read this code and send information to

the computer.

Q No 4: What is the use of computers in retails?

RETAIL

Many retail shops use computer system. Bar code readers are used in stores to directly read the

Universal Production Code (LPC) printed on the each product sold. The receipt produced by thecomputer can include brief description of the items purchased. This information is sent to the

computer to cause an immediate adjustment in the inventory data.

In the case of retail chains linked by networks, the order for a new supply of an item may beautomatically generated and sent electronically to the supply company. These developments have

made shopping much more convenient. The checkout process is faster and the desired item ismore likely to be in stock. In addition the receipts contain much more information than a simple

list of item prices.

Q No 5:

What is e-commerce? How computers can be useful in online

business.

ELECTRONIC COMMERCE

E-commerce consists of the buying and selling of products or services over electronic systems





such as the Internet and other computer networks.

The e-commerce has grown greatly with Internet usage. Various uses of commerce are e-banking,e-shopping, supply of goods, Internet marketing, online ticketing, inventory management

systems, and automated data collection systems.

Electronic commerce that is conducted between two business companies is referred to as

business-to-business or B2B.

Electronic commerce that is conducted between businesses and consumers is referred to as business-to-consumer or B2C. This is the type of electronic commerce conducted by companies

such as Amazon.com.

Q No 6: What is e-banking?

ONLINE BANKING

Online or Internet banking allows customers to conduct financial transactions on a secure website

operated by their banks.

The common features fall broadly into several categories:

Transactional (e.g., account to account transfers, paying a bill, apply for a loan, newaccount, etc.)

Funds transfer between a customer's own checking and savings accounts, or to another

customer's account

Loan applications and transactions

Bank statements

Financial Institution Administration

Q No 7: Briefly describe computer graphics.

COMPUTER GRAPHICS

Computer graphics refers to images or animated motion pictures displaced on monitor or printed

on a printer. A computer-graphics system consists of graphics software that enables a computer to process graphic images. These packages enable a computer to draw, color, shade and manipulatethe images held in its memory.

EXAMPLES

1. Computer graphics is useful in printing, product design and manufacturing, scientificresearch and entertainment.





2. In the business office, computers create graphs and tables to show text information.

3. Computers are used to test various mechanical and electrical properties of complicated

systems in animated motion-picture sequences.

4. Computer graphics is very popular in entertainment industry to create animation of videogames and the special effects in motion pictures.

Q No 8: What is meant by computer simulation? Explain where

computer simulations are used and what are the advantages of using

them?

COMPUTER SIMULATION

Computer simulation is the use of a computer to represent the dynamic responses of one system by the behavior of another system. A simulation uses a mathematical description in the form of a

computer program to show the functional relationships within the real system. When the program

is run, the resulting mathematical model has similar behavior of the real system with the results presented in the form of data. Computer simulations are used in conditions that cannot be easily

or safely applied in real life.

EXAMPLES:

1. A mathematical model used in nuclear experiments.

2. Business models like financial and statistical software that are used in business analysis

and planning.

3. Geometric models are used for applications such as buildings, industrial parts.

4. Simulations of river systems can be used to determine the possible effects of dams andirrigation networks before actual construction has taken place.

Q No 9: Define the following terms:

Computer-Aided Designing (CAD), Computer-Aided Manufacturing (CAM)

COMPUTER AIDED DESIGN (CAD)

Computer programs are used to design the model of a product on the computer. This process iscalled Computer Aided Design or CAD. Due to CAD, we can test the designed product with the

help of computer. When the design is completed successfully, the actual product is manufactured.

The advantages of CAD are many:

1. Designs can be easily changed.





2. The design can be tested using computer modeling. Complex mathematical calculationsare used to predict the item's behavior under normal and extreme conditions.

3.

Plans can be stored.

COMPUTER-AIDED MANUFACTURING (CAM)

CAM is a subsequent computer-aided process after computer-aided design (CAD) and sometimescomputer-aided engineering (CAE).

Computer-aided manufacturing (CAM) is the use of computer software to control machine tools

and related machinery in the manufacturing of work pieces. CAM also refers to the use of acomputer to assist in all operations of a manufacturing plant, including planning, management,

transportation and storage. Its primary purpose is to create a faster production process.

Q No 10:

How computers can be useful in weather forecasting?

WEATHER FORECASTING

Computers are useful in weather forecasting and produce accurate results. Large amount of data iscollected to produce accurate weather forecast. The data is collected from weather stations,

aircraft, airports and satellites. The data consists of physical quantities such as air pressure,humidity, and wind speed and cloud information.

To produce an accurate weather forecast, a powerful computer processes and saves this data so

that it is possible to find out the weather situation in previous years. This information can be used

to predict weather trends.

Q No 11:

Explain how computers can be useful in medical field?

COMPUTERS IN MEDICAL FIELD

Today Computers are an essential part of a hospital. Computers can be used in medical field inthe following ways:

HOSPITAL ADMINISTRATION

We can computerize the accounting, payroll and stock system of the hospital. We can keep therecord of different medicines.

RECORDING MEDICAL HISTORY OF PATIENTS

Computer can be used to store the medical history of the patients. Doctors may better prescribe

the medicines on the basis of the medicines used in past for a particular patient and the results

obtained.

MONITORING SYSTEMS





Many computerized devices are used to monitor the blood pressure, heartbeat and brain of the patients. Computers guide in some surgical operations, too. Computers also monitor heart rates, pulse rates and brain readings. Therefore, we conclude that computers make this possible to deal

with such complicated operations. It would be virtually impossible for a human to do this.

DIAGNOSIS OF DISEASES

Computers are being used to diagnose diseases with the help of software. There are some MedicalSoftware to diagnose diseases and prescribe medicine on the basis of symptoms.

FASTER AND CHEAPER COMMUNICATIONS

Doctors and other staff can use internet to communicate to doctors in other parts of the world, for

sharing information on medical topics or even about a particular patient case. They can exchange pictures, reports and other documents, too.

CLINICAL IMAGE PROCESSING

Computers are being used in Medical Radiology / Diagnostic Imaging. Computers play a role inall types of clinical image processing like CT scan and ultrasound.



CHAPTER 5 COMPUTER ARCHITECTURE


Question & Answers

Q No 1: What is meant by processing?

PROCESSING:

The process of computing the input to achieve the desired results is called processing. Processingis done by the CPU.

Q No 2:

Compare today’s modern microcomputers with the first digital

computers of the 1940s.

1. Digital computer of 1940’s was big in size than today’s modern computer

2. Digital computer of 1940’s was too costly than today’s modern computer.

3. Digital computer of 1940’s was slow in processing than today’s modern computer.

4. Modern computers work with binary numbers (1s and 0s) using the same basic logicoperations as their predecessor.

Q No 3: What is VLSI?

VLSI stands for very large-scale integration; VLSI consists of thousands of electroniccomponents on a single chip. Modern computers are based on VLSI technology.

Q No 4:

Name the basic units of computer system.Basic unit of computer system are: input unit, output unit, processing unit and memory unit.

Q No 5: Draw general block diagram of computer system showing how different

units work together.



CHAPTER 5

muhAmmAd ImrAn AwAn leC

Q No 6: What is CPU? Expla

CENTRAL PROCESSING UN

The ALU and control unit ofProcessing Unit. The CPU is trul

to execute an instruction and inst

Arithmetic Logic Unit

Arithmetic logic unit performs

numbers. The ALL performs osquare roots, exponentials, data

two binary numbers contained i

It consists of logic circuits such a

One operand is stored in theAccumulator Register. The contr

the operation is stored in accumu

Control Unit

The control unit's function is tcontains logic and timing circuit

program one by one. The contr

program is executed. It directs a

by providing timing and control

Q No 7: How ALU executes i

ALU takes one operand stored ithe Accumulator Register. Theresult of the operation is stored i

COMPUTE

urer ImCb I-8/3 IslAmAbAd

in its different units.

T (CPU)

computer are combined into a single unit cy the "brain" of the computer because it generat

ructs other units that performs the operations.

arithmetic, logical and data manipulation oper

erations such as addition, subtraction, multiplomparisons and logical operations such as AN

the two registers named Accumulator and dat

s adders, subtracters, comparators etc.

ata Buffer Register and the other operandol inputs determine the operation to be perform

lator.

fetch, decode and execute the instructions.that generate the signals needed to execute eac

l unit performs these same steps till the last i

d coordinates the operation of all the other part

ignals.

nstructions?

the Data Buffer Register and the other operancontrol unit sends the operation to be perforaccumulator.

ARCHITECTURE

39

lled the Centrales signals needed

ations on binary

ication, division,. OR etc on the

buffer Register.

is stored in theed.. The result of

The control unith instruction of a

nstruction of the

of the computer

that is stored ined to ALU. The





Q No 8:

What is machine cycle? Or what is meant by fetch, decode and execute

instructions.

Machine cycle is a three step process: fetch-decode-execute. Fetch is a process in which an

instruction is taken from memory for execution. This function is performed by Control Unit.Decode is a process in which nature of instruction is examined to determine what operation

should it perform and what data it needs. Execute is a process in which ALU executes theinstruction after getting required data.

Q No 9: Draw general block diagram of ALU

Q No 10: What function the control unit performs?

The control unit performs following functions:

1.

Control Unit fetches decodes and executes the instructions.

2. The control unit directs ALU to execute each instruction of a program one by one.

3. The control unit directs and coordinates the operation of all the other parts of the computer by providing timing and control signals.

Q No 11: What is motherboard?

Q No 12: What is system clock?

SYSTEM CLOCK

System clock generates electric signals and controls all functions of the computer using clockticks. It can tick from 100 million to 1000 million or more times in one second. The speed at

which the CPU executes instructions is called clock speed. Clock speed is measured in MHz.CPU takes 1 to 6 clock ticks to execute one instruction.

Q No 13: Explain main memory of computer and its types.

MAIN MEMORY

Main memory stores instructions that the computer is to execute and data that is needed toexecute that instruction. It also serves as storage for the results of operations performed by the

ALU. The main memory operation is controlled by the control unit using READ or a WRITEoperation. Data written into main memory comes from the ALU or the input unit. Semiconductor

RAM and ROM are commonly used as main memory. Main memory is also known as primary

memory.





RAM

RAM is used for the storage of active programs and data that are needed by CPU for execution.

When the computer starts up, operating system is loaded in RAM. The contents of RAM changecontinuously so it is a temporary memory. Increasing the size of RAM will increase processing

speed of the computer. CPU fetches instruction from the RAM. The disadvantage of RAM is thatit is volatile and will lose all programs if power is turned off.

ROM

ROM stands for Read Only Memory. ROMs are used to store programs that are frequentlyrequired and are not to change during the operation of the computer. The data can be entered inROM during the manufacturing process or may be entered electrically. Because all ROMs are

nonvolatile, these programs are not lost when the computer is turned off.

There are primarily three types of read-only memory. ROM refers to IC chips that are programmed by the manufacturer. A PROM is a semiconductor chip that is obtained from the

manufacturer in an un-programmed state. The user programs it according to his desire.

Another type of ROM called an Electrically Erasable PROM or EEPROM. The EEPROM can bealtered while being used in a logic board by using special power circuits and write pulse

generators. The EEPROM can work like a read/write semiconductor memory while retaining the

nonvolatile nature of ROMs and PROMs.

Q No 14:

When RAM is used?

RAM is used to load programs that will be executed by the CPU. When CPU needs an instructionfor execution, it looks in RAM. Also, when the computer starts up, part of operating system is

loaded in RAM.

Q No 15: What are the types of buses used in computer circuits and what are

their functions?

COMPUTER BUSES

Computer buses are used to transfer data, memory addresses and control signal to and from themicroprocessor to other units.

Address Bus

The address bus is a 16 or above bit bus. It carries the address code from the microprocessor to

the memory unit to select the memory location which the microprocessor is accessing for a Reador Write operation. The address bus is unidirectional bus because information flows in only one

direction.

Data Bus

The data bus is a bidirectional bus over which words of specific bits can be sent from the





microprocessor to memory or from the memory to the microprocessor. The information carried onthis bus may be data or it may be instruction codes fetched by the microprocessor.

Control Bus

The control bus generates control signals needed to coordinate the operations of the

microprocessor with the other units of the microcomputer. Some of the control lines are outputsfrom the microprocessor and others are inputs to the microprocessor from I O devices.

Q No 16: Define register and explain the purpose of the following registers in

computer systems: Program Counter (PC), Data address register (DAR)

Memory Address register (MAR) Instruction Register (IR)

MICROPROCESSOR REGISTERS

Registers serve as dedicated memory locations inside the microprocessor chip used to storevarious kinds of information needed by the microprocessor as it performs functions. Some of theregisters are the followings:

Program Counter (PC)

This register is a counter that controls the sequence in which the instructions are fetched from

memory. At any instant, the contents of the PC indicate the address in memory from which the

next byte of instruction code is to be fetched. Whenever the microprocessor is to fetch a byte ofinstruction code, control signals will place the contents of the PC onto the internal address bus.

The PC count is then incremented to prepare for the next instruction fetch operation.

Data Address Register (DAR)

The DAR provides an operand address to the memory unit when the microprocessor has to accessmemory during the execution phase of an instruction. For example, during the execution of a

store the accumulator instruction, the DAR will hold the operand address corresponding to the

memory location where the content of the accumulator is to be stored.

Instruction Register (IR)

To fetch an instruction from program memory, the microprocessor generates signals that place thecontents of the PC on the address bus, sets the Read/Write operation bit to Read, takes the

resulting memory word from the data bus and loads it into the instruction register (IR). Thus, at

the completion of a fetch operation, the IR holds the instruction.

Accumulator (A) and Data Register (DR)

These two registers hold the operands that the ALU operates on during the execution phase of an

instruction. The result of an ALU operation is then transferred to the accumulator.





Q No 17:

Explain three basic types of instruction code formats used in

computers.

INSTRUCTION CODE

An instruction code is a group of bits that tells the computer to perform a specific operation. It is

divided in parts, each having its own meaning. The basic part of an instruction code is operation

part. The operation code of an instruction is a group of bits that define operations as add, subtract,multiply, shift, and complement. The number of bits required for 2n operations are n bits.

An operation is part of an instruction stored in computer memory. It is a binary code that tells thecomputer to perform a specific operation. The control unit receives the instruction from memory

and reads the operation code bits. It then issues a sequence of control functions that performmicro-operations in internal computer registers.

An instruction code must specify not only the operation but also the registers and or the memorywords where the operands are to be found. Memory words can be specified in instruction codes

by their address.

If an operation in an instruction code does not need an operand from memory, the rest of the bits

in the instruction can be used for other purposes. For example, operations such as clear AC andincrement AC operated on data stored in the AC register.

It is sometimes suitable to use the address bits of an instruction code not as an address but as theactual operand. When the second part of an instruction code specifies an operand, the instruction

is said to have an immediate operand. When the second part specifies the address of an operand,the instruction is said to have a direct address. If the bits in the second part of the instruction

select an address of a memory word in which the address of the operand is found, it is called in-direct addressing. For computer having direct and indirect addressing, we take first bit of

instruction as 0 for direct addressing and 1 for indirect addressing.

Q No 18: What is an instruction code? Define its different parts.

INSTRUCTION CODE

An instruction code is a group of bits that tells the computer to perform a specific operation. It is

divided in parts, operation code (opcode) and operand code. The operation code of an instruction

is a group of bits that define operations as add, subtract, multiply, shift, and complement. Theoperand code stores the registers and memory words where the operands are to be found. Memory

words can be specified in instruction codes by their address.

Q No 19: What is op-code? How can you determine the number of operations

performed by computers?

OPCODE

The operation code of an instruction is a group of bits that define operations as add, subtract,





multiply, shift, and complement. The number of bits required for 2n operations are n bits. Forexample, if a computer can perform 32 operations, then op-code contains 5 bits.

Q No 20: What is meant by direct and indirect address instructions?

In an instruction code, if the second part specifies the address of an operand, the instruction is saidto have a direct address. If the bits in the second part of the instruction select an address of a

memory word in which the address of the operand is found, it is called in-direct addressing. For

computer having direct and indirect addressing, we take first bit of instruction as 0 for directaddressing and 1 for indirect addressing.

Q No 21: What is immediate operand instruction?

In an instruction code, if the second part of an instruction code specifies an operand, the

instruction is said to have an immediate operand.

Q No 22: Give some examples of computer instructions with their description.

COMPUTER INSTRUCTIONS

Computer instructions are stored in consecutive memory locations and are executed sequentiallyone at a time. The control unit reads an instruction from a specific address in memory and

executes it. It then continues by reading the next instruction in sequence and executes it, and soon.

The memory unit has a capacity of 4096 words and each word contains 16 bits. Twelve bits of an

instruction word are needed to specify the address of an operand. This leaves four bits for the

operation part of the instruction. However, only three bits are used to specify an operation code.The fourth bit is used to specify a direct or indirect addressing mode.

The basic computer has three different instruction code formats. The operation part of theinstruction contains three bits: the meaning of the remaining thirteen bits depends on the

operation code encountered.

A memory-reference instruction uses the last 12 bits to specify an address and the first bit tospecify the mode I.

A register-reference instruction specifies an operation on or a test of the AC or E register. Anoperand from memory is not needed. Therefore, the last 12 bits are used to specify the operation

or test to be executed. A register-reference instruction is recognized by the operation code 111

with a 0 in the first bit of the instruction.

Input-output instruction does not need a reference to memory and is recognized by the operationcode 1111 with a 1 in the first bit of the instruction. The remaining 12 bits are used to specify the

type of input-output operation or test performed.

Only three bits of the instruction are used for the operation code. It may seem that the computer is





restricted to a maximum of eight distinct operations. However, since register-reference and input-output instructions use the remaining 12 bits as part of the operation code, the total number of

instructions can exceed eight.

Q No 23:

Define system software. Explain its types.

SYSTEM SOFTWARE

System software is used to control the activities of the computer and to make the use of computermore effective. It is can be subdivided into three categories, that is: operating systems, operating

environment and utilities.

Operating Systems

A computer's operating system enables it to carry out its disk filing and other operational tasks.We can put most of these tasks under four headings:

1. Disk operations which are to do with storing programs and data on disk

2. Network operations which enable a number of computers to be linked to each other and toshare facilities such as hard disks and printers

3. Multi-tasking which enables the computer to handle several tasks at the same time

4. Multi-user operations which allow a number of people to use the computer and itssoftware at the same time

5. Input/output management tasks to handle input output devices

6. Process management for executing processes on the processing unit

Operating Environment

Operating systems provide two kinds of environments for the user to interact with the system:Command Line Interface and Graphical User Interface

In Command line interface environment, user needs to type commands to perform any task, that isa difficult task, so these type of environments are not user-friendly. DOS provides CLI.

In Graphical user interface, user can interact with the system using WIMP (meaning 'Window,

Icon, Mouse, and Pointer’). User doesn’t need to remember commands. So these are user-friendlyenvironments. Windows and Linux provide GUI.

Utilities

These provide the facilities carrying out tasks which are beyond the capabilities of the operatingsystem in a more efficient and easier way. Examples of utilities include Windows Explorer and

programs that we run from control panel for setting the time and date, installing new hardware

such as modem scanner and mouse settings etc.




Q No 24:

What is WIMP?

In Graphical user interface, user can interact with the computer using WIMP (meaning 'Window,

Icon, Mouse, and Pointer’). So user doesn’t need to remember commands. Windows and Linux provide GUI.

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