Computer Network and Data Communication

INTRODUCTION

Definition of terms

i) Network
A collection of independent entities that are arranged in such a manner to exchange data,
information or resources e.g Road networks, telephone networks.
ii) Computer networks
A collection of computers linked together using transmission media for the purpose of communication and resource sharing

iii) Transmission Media
is a physical and non-physical link between two or more computers and in which a signal can be made to flow from source to destination

iv) Resource Sharing
Is the sharing of the resources that are attached to the network for access by users eg file, printers , data, application programs etc

v) Data Communication
A process of transmitting data signal from one point to another through the network

vi) Telecommunication
The communication i.e. transferring of data and information over significant distances is known as telecommunication.

Advantages of computer network are:

    Data and software of computer can be shared with other computer on the network.
    Only the authorized user of a network can use the facilities of the network.
    Computers on the network can communicate with each other.

The disadvantages of computer network are:

    Data and information may be stolen by computer hackers if the security of network is not reliable.
    If any computer in a network gets affected by computer virus, there is high chance of spreading computer viruses on the other computer.
    Computers on the network have to depend on the server computer for resources.
    This sharing of information may leak the privacy of other clients.

Explain how computer network reduce expenses in an office.
- Computer Networks can allow businesses to reduce expenses and improve efficiency by sharing data and common equipment, such as printers, among many different computers. At the same time, the network may be connected through cables, telephone lines, infrared beams etc, which is cheaper and helps to reduce the expenses.

TERMS USED IN DATA COMMUNICATION

i) Data signal
Is a voltage signal level in the circuit which represents the flow of data. This can be either Analog or
Digital in nature
ii) Signal modulations and Demodulation
Is a process of converting data signal to and from a form that is suitable for transmission over a
transmit-ion medium.
MODEM - Converts digital signal by superimposing it on an analog carrier signal which is transmitted
over analog telephone line. A process known as Modulation
A modem at the receiving end converts the analog signal into digital form a process called
Demodulation.

iii) Multiplexing
Is a process of sending multiple data signals over the same medium e.g a wire conductor can carry several data signal either simultaneously or at different times.
De multiplexing
A process of separating the multiplexed signals at the receiving end.

iv) bandwidth
- Is a maximum amount of data that the transmission medium can carry at any one time. e.g a cable having a bandwidth of 100 mbps.
v) Bases-band
- A digital signal that is generated and applied to transmission medium directly without modulation.
- It utilities the full capacity of transmission medium hence at any time, only one signal can be sent unless they are multiples.

vi) Attenuation/ Signal loss
- Is the decrease in magnetite and energy as a signal progressively move along a transmission medium. The signal is not boosted, it will totally be lost along the way and may never reach the destination.
- It corrected by placing a signal amplifier ( repeater station) along the medium at appropriate distances in order to receive the weak signal, clean it, amplify it then restart it.

MODES OF DATA COMMUNICATION
There are three modes of data communication
i) Simplex
ii) Half Duplex
iii) Full Duplex

1. Simplex
Communication in only one direction e.g radio broadcast. The listener cannot communicate back through radian receiver

2. Half Duplex
- Communication in both direction but one direction at a time e.g sender sends information then the receiver can reply e.g radio call

3.Full Duplex
- Communication occurs in both directions simultaneously e.g a computer sending and receiving data on a network.

TYPES OF COMPUTER NETWORKS
Types of computer networks are classified according to size. There are three common networks
1. Local Area Network


2. Metropolitan Area Network

3. Wide Area Network

TYPES OF NETWORK TYPOLOGIES

- Refers to the way which computers and other devices have been arranged or how data is passed from one computer to another in a network
- Topology is viewed in two ways
1. Logical Topology/ Signal Topology
- Deals with the way data passes from one device to the next in the network e. g Ethernet and Token Ring


2. Physical Topology
- Refers to the physical layout or arrangement of components on the network e.g Star, Bus, Ring, Mesh, Tree/Hierarchical Typologies


1. Bus Topology
Alternatively referred to as a line topology, a bus topology is a network setup in which each computer and network device are connected to a single cable or backbone. The following sections contain both the advantages and disadvantages of using a bus topology with your devices.

Advantages of bus topology

    It works well when you have a small network.
    Easiest network topology for connecting computers or peripherals in a linear fashion.
    Requires less cable length than a star topology.

Disadvantages of bus topology

    Difficult to identify the problems if the whole network goes down.
    It can be hard to troubleshoot individual device issues.
    Not great for large networks.
    Terminators are required for both ends of the main cable.
    Additional devices slow the network down.
    If a main cable is damaged, the network fails or splits int


2. Ring Topology
A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet.

Advantages of ring Topology

    Very orderly network where every device has access to the token and the opportunity to transmit
    Performs better than a bus topology under heavy network load
    Does not require a central node to manage the connectivity between the computers
    Due to the point to point line configuration of devices with a device on either side (each device is connected to its immediate neighbor), it is quite easy to install and reconfigure since adding or removing a device requires moving just two connections.
    Point to point line configuration makes it easy to identify and isolate faults.
    Reconfiguration for line faults of bidirectional rings can be very fast, as switching happens at a high level, and thus the traffic does not require individual rerouting.

Disadvantages of Ring Topology

    One malfunctioning workstation can create problems for the entire network. This can be solved by using a dual ring or a switch that closes off the break.
    Moving, adding and changing the devices can affect the network
    Communication delay is directly proportional to number of nodes in the network
    Bandwidth is shared on all links between devices
    More difficult to configure than a Star: node ad junction = Ring shutdown and reconfiguration


3. Star Topology

Star networks are one of the most common computer network typologies. In its simplest form, a star network consists of one central node, typically a switch or hub, which acts as a conduct to transmit messages. In star topology, every node (computer workstation or any other peripheral) is connected to a central node. The switch is the server and the peripherals are the clients.
Advantages

    If one node or its connection breaks it doesn’t affect the other computers and their connections.
    Devices can be added or removed without disturbing the network

Disadvantages

    An expensive network layout to install because of the amount of cables needed
    The central hub is a single point of failure for the network

4. Mesh Topology
A mesh network is a network topology in which each node relays data for the network. All mesh nodes cooperate in the distribution of data in the network. It can be applied to both wired and wireless networks.
Advantages of Mesh topology
1) Data can be transmitted from different devices simultaneously. This topology can withstand high traffic.
2) Even if one of the components fails there is always an alternative present. So data transfer doesn’t get affected.
3) Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages of Mesh topology
1) There are high chances of redundancy in many of the network connections.
2) Overall cost of this network is way too high as compared to other network typologies.
3) Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.



Switch Bridge Packet forwarding in Switches are performed using A Sics (Application Specific Integrated Circuits). Packet forwarding in Bridges are performed using software. Work at higher speed. Work at lower speed. Switches have more ports. Bridges have less port. Switches can operate on half and full duplex mode. Bridges can operate on half duplex mode only.

Router Gateways Coordinates data transfer within internal network. Coordinates data transfer from internal network to internet. All the functionality of gateways are in router. Gateways are integrated into the router. Always have to have a hardware to function. Some software also can perform as gateways.

Internet and E-mail

The Internet

The Internet links private PCs, public networks and business networks together using telephone lines to form one vast world-wide network.
It allows computer users to share and exchange information with each other wherever they are in the world.
The information on the Internet comes in many different formats.
These range from simple e-mail text files to music, video clips, computer software and even live television pictures.

The simplest way to connect to the Internet is to use a dial-up connection.
This type of connection requires a computer with a modem and access to a telephone line.
A modem converts a digital signal into an equivalent analogue signal that can be sent down a telephone line.
At the destination another modem is needed to convert the analogue signal back into a digital signal, which the receiving computer can understand.

The speed of a modem is measured in kilobits per second (Kbps) – this is a measure of how fast data can be transferred.
Dial-up modem connections offer data transfer speeds of up to 52 Kbps.
ISDN digital telephone lines offer a faster connection to the Internet.
ISDN connections offer data transfer speeds of up to 128 Kbps.
Dialup modems and ISDN lines are gradually being replaced by broadband connections that use a system called ADSL.
Broadband connections allow round-the-clock Internet access without having to dial a special telephone number and wait for a connection to be established.
ASDL is much faster than ISDN typically offering data transfer speeds of between 500 Kbps and 1,000 Kbps.
Some larger organisations use a leased line as their method of connection.
This is a private telephone line which is permanently open 24 hours a day.

An Internet Service Provider is a commercial organisation, which provides a connection to the Internet for other businesses or individuals.
Search engines allow users to surf the Internet for information by entering keywords.
Web addresses give the location of individual sites on the World Wide Web.
A web site can be quickly accessed using its address which is often referred to as a URL or Uniform Resource Locator.
A Uniform Resource Locator or URL gives the location of an individual site on the World Wide Web
Most URLs start with http//:www.
URLs often reveal the country of origin such as .uk for the United Kingdom.
URLs also indicate whether a site is commercial with either .co or .com for a commercial organisation, .gov for a government organisation and .ac for academic organisations.

Many businesses now have websites that allow Internet users to buy their goods or services online at any time of day or night throughout the year.
This type of online shopping also offers the advantages of not needing to travel anywhere or get pushed around in crowded shops.
Some companies do all of their business over the Internet and have no ordinary shops.

Advantages of online shopping:
money doesn’t have to be spent on normal business overheads like renting shops and paying employees;
customers can be offered a much wider choice of goods because they can be ordered from suppliers as required rather than having to be kept available on the shelves all the time;
money is not tied up in unsold stock or wasted on products that aren’t popular;
data about customers and their buying habits can be collected directly and used to offer a much more personalised service tailored to suit the needs of an individual customer.

Disadvantages of online shopping:
debit or credit card numbers can be intercepted by hackers during transmission and used to make unauthorised purchases;
criminals can set up fake web sites offering goods or services often using the name of a genuine company;
it is much easier for a business to gather information about its rivals by simply accessing their web sites — this can make it much harder to remain competitive.

Online booking systems allow Internet users to check the availability of and book things like:
theatre, cinema and concert tickets; seats on coaches, trains and aeroplanes; hotel rooms.
An online booking system is essentially a web site that can be used to access a remote database.

Dangers of the Internet:

hackers;
viruses;
undesirable material.

Hackers can be stopped using firewall software.
Viruses are often spread via e-mail and can be removed using virus checking programs.
Undesirable material can be blocked using special filtering software and adult supervision.

Advantages of the Internet:

easy communication with other people around the world;
valuable learning resource because Internet skills will be needed for jobs in the future;
enables more people to work from home;
a vast amount of information can be accessed;
up-to-date information can be accessed on-line without the need to await publication;
publishing documents on the Internet saves paper;
a valuable resource for companies to advertise and conduct business.



Disadvantages of the Internet:

much of the information isn’t checked and may be incorrect or irrelevant;
a large amount of undesirable material, such as pornography, is readily available;
messages sent across the Internet can be easily intercepted and are open to abuse by others;
large telephone bills can easily be run up;
too much time spent on the Internet could result in a lack of face-to-face interaction with others and a loss of social skills;
going on-line runs the risk of hackers or viruses being able to damage your computer.

Operating Systems

Is a software that acts as an interface between the user, application software and the computer hardware

EXAPMLE OF OPERATING SYSTEM

1. Microsoft Disk operating system ( Ms DOS)
2. Windows ( 98, 2000, XP, vista)
3. Linux
4. Unix

PARTS OF OPERATING SYSTEM

1. Shell – it is the outer part of an operating system and it is responsible of interacting with the operating system
2. Kernel – Responsible for managing and controlling computer resources such as the processor, main memory, storage devices, input devices, output devices and communication devices

RESOURCE UNER THE OPERATING SYSTEM CONTROL

• The processor
• Main memory
• Input/Output Device
• Secondary storage devices
• Communication devices and ports

FUNCTIONS OF OPERATING SYSTEM

1. Job scheduling

– it is the process of the operating system to keep list of jobs currently being run by the computer and clocking them in and out of the processor.

1. Interrupt handling

• It is a break from the normal sequential processing of instructions in a program

1. Resource control and allocation

• It is situation where the processor gives a computer resources a unique number called interrupt number so that it can be able to recognize and prioritize it.

1. Memory Management

• It is where the operating system constantly assigns main memory storage partitions to data an instructions

1. Error handling

• It is a situation whereby an operating system alerts the user of errors that arises in ease of illegal operations, hardware or software failure.

1. Input/output handling

NOTE
What is interrupt request?

• Is a unique number that is given to a resource for identification purposes

What is the importance of interrupt computer

• To enable urgent tasks/ processes to b given the first priority during program execution

What is virtual memory

• Part of the hard disk that acts as maim memory
• Operating system organizes the main memory in blocks called page frames. The processes are divided into partitions that can fit in a page. The operatind system swaps these pages between the main memory and the hard disk. The part of the hard disk where these pages are held in the virtual memory.

What is a deadlock

• Is where a particular task holds a resourcs and refuses to release it for othe tasks to use.

CLASSIFICATION OF OPERATING SYSTEM
They are classified into three ways/types:-

1. According to the number of tasks handled concurrently
2. Single task – one task is operated at a any given time
3. Multi-Task – More than one task is processed apparently simultaneously

1. According to the number of users
2. Single user – Single (One) user operates a computer at any given time
3. Multi user – More than one user can operate the computer at the same time

1. Human computer interface / G U I

• Interaction between the computer and the user.

1. Command line – The user types the commands at the command prompt to activate them by pressing the enter key

Advantages

• Fast in operation by experienced users
• flexible
• Use Less memory
• Don’t require expensive hardware

Disadvantages
- Hard to learn and understand
- Not user friendly
- If you mistype or forgot the syntax of writing the command, you cannot operate it
- Difficult to learn
- Difficult to move information from one application to another
- Difficult to design and produce printed reports
- Do not support multi-users and multi-task

1. Menu driven – The user is provided with a list of menu to choose from

Advantages

• More user friendly than command line
• More easier to learn and understand
• Eliminates the problem of forgetting the syntax of command since commands are provided for you

Disadvantages

• Slow to operate
• Not flexible

1. Graphical User Interface(GUI) – The user interacts with the computer using icons and menus and select them using pointer

Advantages
- It is easy to learn and operate
- They make it easy to exchange information between application
- Reduce the user training time and cost due to their inform mode of operation
- It is more user friendly
- Supports multi user and multi task

Disadvantages

• Cost of GUI supporting hardware is higher
• Many objects on the GUI confuse new computer users
• - Require faster processors that are more expensive

WINDOW as used in operating system
Is a rectangular object created on a screen by operating system to contain input or output data for a particular program
PROPERTIES OF A WINDOW

• Title bar
• Display/ working area
• Horizontal and vertical scrolls bars
• Menu bars
• Status bar
• Tool bar

TYPES OF MENUS

1. Pop up menu
2. Pop down menu
3. Sub menu( Cascading/ Side kick menu)

COMPUTER FILES
Are classifies into types :-

1. System Files

Are files that contain information that is critical to the operations of the computer

1. Application Files

Are files that holds programs or application files

The Total Computer System

 

 Introduction & System theory.

Meaning and Elements of Computer Systems

Computer Systems

 

We are all aware of what computers are and their immense importance in our daily lives. It is an electronic device that not only stores data but also processes and manipulates data to carry out functions. Upon receiving valid instructions, a computer can perform a variety of operations.
What allows us to perform such tasks on the computer is a computer system. A computer system is the sum total of all the components (hardware and software) that makes up a fully functional computer.

Elements of a Computer System
There are six main elements that make up a computer system. They all interact with each other and perform the task at hand. Let us take a look at all of them.

1] Hardware

 

These are all the physical aspects of a computer system. They are tangible, i.e. you can see and touch them. Hardware components are the electronic r mechanical instruments, like keyboard, monitor, printer etc. They help the users interface with the software, and also display the result of the tasks being performed.
Hardware can actually be of four types, depending on which function they perform. The four types of hardware are,

• Input Hardware: For users to input data into the computer system. Examples: Keyboard, mouse, Scanner
• Output Hardware: To translate and display the result of the data processing =. Example: Monitor Screen, Printer etc
• Processing and Memory Hardware: Where data and information are processed and manipulated to perform the task at hand. It is also the workspace of the computer, where it temporarily stores data. Examples: Central Processing Unit (CPU), Read Only Memory (RAM)
• Secondary Storage Hardware: Where the computer system stores data permanently. Example: Hard disk, Pen drive etc

2] Software

 

Software is nothing but a set of programmes (computer instructions), which helps the user to do a set of specific tasks. It helps the user interact with the computer system with the help of hardware. Software, as you can imagine, is the intangible aspect of the computer system.
Basically, there are six main types of software, which are as follows,

• Operating System: These specialized programmes allow the communication between software and hardware. The operating systems run all the other computer programmes, and even regulate the startup process of the computer. Examples: Windows XP, Macintosh etc
• Application Software: These are designed to perform a specific task or a bunch of tasks. They can be user-designed (specific to the user’s needs) or readymade application software. Example: PowerPoint, Tally etc.
• Utility Software: Like operating systems, it is a system software. It helps maintain and protect the computer system. For example, Anti-virus software is a utility software.
• Language Processors: Software that interprets computer language and translates it into machine language. It also checks for errors in language syntax and fixes the problems.
• System Software: This types of software control the hardware, the reading of the data and other such internal functions.
• Connectivity Software: The special software that facilitates the connection between the computer system and the server. This allows the computer to share information and communicate with each other.

3]Liveware

 

The people interacting with the computer system are also an element of it. We call this element the Liveware. They are the ultimate “users” of the computer systems. There are three types of people that interact with the system, namely

• Programmers: Professionals who write the computer programs that allow users to interact with the computer. They must have technical knowledge of computers and computer languages.
• System Analyst: They mainly design data processing systems, and solve problems that arise in data processing
• End-Users: Also known as operators, they are the people who interact with the computer system.

4] Procedures

These are a set of instructions, written in code, to instruct a computer on how to perform a task, run a software, do calculations etc. There are three types of procedures in a computer They are,

• Hardware-Oriented Procedure: Instructs the hardware components of the system, ensures they work smoothly
• Software Oriented Procedure: Provides instructions to launch and run software programs
• Internal Procedures: Directs the flow of information and sequences the data

5] Data

 

Data is essentially the raw facts and figures that we input in the computer. The data gets processed via the computer system and becomes information, which is processed and organized data. Information can then be used for decision-making purposes.
The measurement of data is done in terms of “bytes”. One kilobyte (KB) is approximately 1000 bytes, 1 megabyte (MB) is 1 million bytes and finally, 1 gigabyte (GB) is approximately 1 billion bytes.

6] Connectivity

This is when the computers are linked to a network. It facilitates sharing of information, files, and other facilities. Computers can connect to a network via LAN cables, Bluetooth, Wi-Fi, satellites etc. The internet is the most obvious example of connectivity in a computer system.

Introduction of computers

Computer : is an electronic device that operates (works) under the control of programs stored in its own memory unit.
A computer is an electronic machine that processes raw data to give information as output.

An electronic device that accepts data as input, and transforms it under the influence of a set of special instructions called Programs, to produce the desired output (referred to as Information).

Explanations;
A computer is described as an electronic device because; it is made up of electronic components and uses electric energy (such as electricity) to operate.

A computer has an internal memory, which stores data & instructions temporarily awaiting processing, and even holds the intermediate result (information) before it is communicated to the recipients through the Output devices.

It works on the data using the instructions issued, means that, the computer cannot do any useful job on its own. It can only work as per the set of instructions issued.

A computer will accept data in one form and produce it in another form. The data is normally held within the computer as it is being processed.


Program:
A computer Program is a set of related instructions written in the language of the computer & is used to make the computer perform a specific task (or, to direct the computer on what to do).

A set of related instructions which specify how the data is to be processed.
A set of instructions used to guide a computer through a process.

Data: Is a collection of raw facts, figures or instructions that do not have much meaning to the user.

­ Data may be in form of numbers, alphabets/letters or symbols, and can be processed to produce information.

TYPES OF DATA.
There are two types/forms of data:

a). Digital (discrete) data:
Digital data is discrete in nature. It must be represented in form of numbers, alphabets or symbols for it to be processed by a computer. Digital data is obtained by counting. E.g. 1, 2, 3 …



b). Analogue (continuous) data:
Analogue data is continuous in nature. It must be represented in physical nature in order to be processed by the computer. ­ Analogue data is obtained by measurement. E.g. Pressure, Temperature, Humidity, Lengths or currents, etc.­ The output is in form of smooth graphs from which the data can be read.
Data Processing:
It is the process of collecting all items of data together & converting them into information.

Processing refers to the way the data is manipulated (or handled) to turn it into information.
The processing may involve calculation, comparison or any other logic to produce the required result. The processing of the data usually results in some meaningful information being produced.

Information: is the data which has been refined, summarized & manipulated in the way you want it, or into a more meaningful form for decision-making. ­ The information must be accurate, timely, complete and relevant.

Characteristics / Features of a Computer.

Before 20th century, most information was processed manually or by use of simple machines. Today, millions of people are using computers in offices and at home to produce and store all types of information

The following are some of the attributes that make computers widely accepted & used in the day-to-day activities in our society:

1. Speed.
Computers operate at very high speeds, and can perform very many functions within a very short time.
They can perform a much complicated task much faster than a human being.
The speed of a computer is measured in Fractions of seconds.
Millisecond - a thousandth of a second (10-3)
Microsecond - a millionth of a second (10-6)
Nanosecond - a thousand millionth of a second (10-9)
Picosecond - a million millionth of a second (10-12)

The speed of a computer is usually linked to the technology used to build it.

a). 1st Generation computers (1940s & early 1950s).

• The computers were built using Vacuum tubes, and the speed was measured in Milliseconds. E.g., a computer could perform 5,000 additions & 300 multiplications per second.

b). 2nd Generation computers (1950s & early 1960s).
Were built using Transistors. Their operation speeds increased & were measured in Microseconds. E.g., a computer could perform 1 million additions per second.

c). Mid 1960s.
Integrated Circuit (IC), which combined a no. of transistors & diodes together on a silicon chip, was developed. The speed increased to tens of millions of operations per second.

d). In 1971, Intel Corporation produced a very small, single chip called a Microprocessor, which could perform all the operations on the computer’s processor. The chip contained about 1,600 transistors.

e). Today’s microprocessors are very powerful, cheaper & more reliable due to the use of the Large Scale Integration (LSI) & Very Large scale Integration (VLSI) technologies, which combines hundreds of thousands of components onto a single chip.
The computer speeds are now measured in Nanoseconds & Picoseconds.

2. Accuracy:
Unlike human beings, computers are very accurate, i.e., they never make mistakes.
A computer can work for very long periods without going wrong. However, when an error occurs the computer has a number of in-built, self-checking features in their electronic components that can detect & correct such errors.
Usually errors are committed by the users entering the data to the computer, thus the saying Garbage in Garbage Out (GIGO).
This means that, if you enter incorrect data into the computer and have it processed, the computer will give you misleading information.

3. Reliability.
The computer can be relied upon to produce the correct answer if it is given the correct instructions & supplied with the correct data.

Therefore, if you want to add two numbers, but by mistake, give the computer a “Multiply” instruction, the computer will not know that you intended to “ADD”; it will multiply the numbers supplied.

Similarly, if you give it the ADD instruction, but make a mistake and enter an incorrect data; let say, 14 & 83 instead of 14 & 38; then the computer will produce the “wrong” answer 97 instead of 52. However, note that, 97 is ‘correct’ based on the data supplied.

Therefore, the output produced by a computer is only as reliable as the instructions used & the data supplied.

4. Consistency:

Computers are usually consistent. This means that, given the same data & the same instructions, they will produce the same answer every time that particular process is repeated.

5. Storage:

­ A computer is capable of storing large amounts of data or instructions in a very small space.

­ A computer can store data & instructions for later use, and it can produce/ retrieve this data when required so that the user can make use of it.

­ Data stored in a computer can be protected from unauthorized individuals through the use of passwords.

6. Diligence:

Unlike human beings, a computer can work continuously without getting tired or bored. Even if it has to do a million calculations, it will do the last one with the same speed and accuracy as the first one.

7. Automation:

A computer is an automatic device. This is because, once given the instructions, it is guided by these instructions and can carry on its job automatically until it is complete.

It can also perform a variety of jobs as long as there is a well-defined procedure.
8. Versatile:

A computer can be used in different places to perform a large number of different jobs depending on the instructions fed to it.

9. Imposition of a formal approach to working methods:
Because a computer can only work with a strict set of instructions, it identifies and imposes rigid rules for dealing with the data it is given to process.


CLASSIFICATION OF COMPUTERS
Computer exist in different sizes, weight and shapes
The major ways in which computers are classified are
i) Classification according to Functionality
In this category, computers are categorized cording to the way they process data and kind of data a computer can process.
Example of this data are,
a) Analog Data
b) Digital data

ii) Classification according to the purpose
iii) Classification according to physical size
iii) classification according to functionality


ACCORDING TO PHYSICAL SIZE

TYPES OF COMPUTER




Analog computer
Analog computer measures and answer the questions by the method of “HOW MUCH”. The input data is not a number infect a physical quantity like temp, pressure, speed, velocity.

• Signals are continuous of (0 to 10 V)
• Accuracy 1% Approximately
• High speed
• Output is continuous

Time is wasted in transmission time

ANALOG COMPUTER

DIGITAL COMPUTERS
Digital computer counts and answer the questions by the method of “HOW Many”. The input data is represented by a number. These are used for the logical and arithmetic operations.

• Signals are two level of (0 V or 5 V)
• Accuracy unlimited
• low speed sequential as well as parallel processing
• Output is continuous but obtain when computation is completed.

MICRO COMPUTERS
Micro computer are the smallest computer system. There size range from calculator to desktop size. Its CPU is microprocessor. It also known as Grand child Computer.

• Application : - personal computer, Multi user system, offices.

MINI COMPUTERS
These are also small general purpose system. They are generally more powerful and most useful as compared to micro computer. Mini computer are also known as mid range computer or Child computer.

• Application :- Departmental systems, Network Servers, work group system.

MAINFRAME COMPUTERS
Mainframe computers are those computers that offer faster processing and grater storage area. The word “main frame” comes from the metal frames. It is also known as Father computer.

• Application – Host computer, Central data base server.

SUPER COMPUTERS

• Super computer are those computer which are designed for scientific job like whether forecasting and artificial intelligence etc. They are fastest and expensive. A super computer contains a number of CPU which operate in parallel to make it faster. It also known as grand father computer.
• Application – whether forecasting, weapons research and development.

CLASSIFICATION OF DIGITAL COMPUTERS

• Desktop
• Workstation
• Notebook
• Tablet PC
• Handheld computer
• Smart Phone

WORKSTATION

TABLET PC



HANDHELD PC (PDA)



SMART PHONE