Unit 1: Computer System Class 11 Computer Notes | Based On New Syllabus

Chapter 1: Computer System

Introduction of Computer

A Computer is an electronic device operating under the control of instructions stored in its own memory that can accept data (input), process the data according to predefined set of rules, produce information (output) and store the information for future use.

Functionalities of a Computer

1. Takes data as input.
2. Stores the data/instructions in its memory and uses them when required.
3. Processes the data and converts it into useful information.
4. Generates the output.

Required hardware components of General-purpose Computer:

1. Input Device: It is the medium through which data and instructions are given to the computer. E.g. Keyboard, Mouse, Joystick, trackball, etc.
2. Output Device: It is the device which is responsible for displaying the result. E.g. Monitor, printer, speaker, etc.
3. Memory: Enables a computer to store, at least temporarily, data and programs.
4. Mass Storage Device: Allows a computer to store huge amounts of data permanently.
5. CPU: The heart of the computer, this is the component that actually executes the instructions.

Some Terminology:

1. Data: Data is the plural form of the word datum. Data can be defined as any raw fact, figure, observation, or collection about any object, which can be recorded in the form of text, number, sound, or image.
2. Information: Information is the processed data which we get in the required form. So, it is very meaningful and useful to us.
3. Process: Processing is the conversion of input (data) into output (information) which is done by the processing unit of the computer.
4. Instruction: Instruction is a command given to the computer to perform a specific task.
5. Program: Program is a set of instructions to perform a specific task in a computer. Also called the component of software.
6. Input: Any instructions or data sent to a computer for processing is considered input. Input or user input is sent to a computer using an input device.
7. Output: The result generated after processing the data is called output.
8. Storage: Storage is the process of saving data and instructions permanently for future use.
9. Memory: Memory is a device that is used to store data and instructions.
10. Hardware:Computer hardware is the collection of physical components that make up a computer. In other words, we can say that hardware covers all parts of a computer that are tangible objects. Examples keyboard, mouse, scanner, printer, speaker, memory, etc.
11. Software: Software is a collection of computer programs that performs different tasks on a computer system. Software refers to something intangible. Basically, software is written by programmer. Software is divided into two types:
    • System Software: System software is a set of programs that control and manage the operations of computer hardware. It also helps application software to run properly. Examples of system software are Operating System, Language Translator, Utility Programs, etc.
    • Application Software: Application software is a set of programs that perform specific tasks for users. Examples of application software are MS Word, MS Excel, MS PowerPoint, etc.
12. Firmware: A set of micro instructions stored in a chip is called firmware. Micro instructions are hardware level instructions which are directly executed by the hardware. Firmware loaded into the equipment, either at the time of manufactured or later. Firmware is held in non-volatile memory devices such as ROM.
Note:
1. Volatile memory: It is a type of computer memory whose contents are erased when the system's power is turned off. For example, RAM
2. Non-volatile memory: It is a type of computer memory that has the capability to hold saved data even if the power is turned off. For example, ROM

Units of Measurement - Storage

Unit	Shortened	Capacity
Bit	b	1 or 0 (on or off)
Byte	B	8 bits
Kilobyte	KB	1024 bytes
Megabyte	MB	1024 kilobytes
Gigabyte	GB	1024 megabytes
Terabyte	TB	1024 gigabytes
Petabyte	PB	1024 terabytes
Exabyte	EB	1024 petabytes
Zettabyte	ZB	1024 exabytes
Yottabyte	YB	1024 zettabytes

Units of Measurement - Speed

1 Hz = 1 cycle per second

1 MHz = 1 million cycles per second

1 GHz = 1 billion cycles per second

Characteristics of Computer

1. Word length:A digital computer operates on binary digits i.e 0 and 1. It can understand information only in terms of 0s and 1s. A binary digit is called a bit. a group of 8 bits is called a byte. The number of bits that a computer can process at a time in parallel is called its word length. Commonly used word length are 8,16,32 or 64 bits. Word length is the major of the computing power of a computer. When we talk of a 32-bit computer, it means that it's word length is 32 bits.
2. Speed: A digital computer operates on binary digits i.e 0 and 1. It can understand information only in terms of 0s and 1s. A binary digit is called a bit. a group of 8 bits is called a byte. The number of bits that a computer can process at a time in parallel is called its word length. Commonly used word length are 8,16,32 or 64 bits. Word length is the major of the computing power of a computer. When we talk of a 32-bit computer, it means that it's word length is 32 bits.
3. Storage:The computer has main memory and auxiliary memory. The computer can store a large amount of data. With more and more auxiliary storage devices, which are capable of storing huge amounts of the data, the storage capacity of a computer is virtually unlimited. The reason that makes computer storage unique is not that it can store huge amount of data, but the fact that it can retrieve the information that the user wants in a few seconds. For example, computer dictionaries are available and the contents of this software version are the same as that of the printed dictionary.
4. Accuracy: The computer has main memory and auxiliary memory. The computer can store a large amount of data. With more and more auxiliary storage devices, which are capable of storing huge amounts of the data, the storage capacity of a computer is virtually unlimited. The reason that makes computer storage unique is not that it can store huge amount of data, but the fact that it can retrieve the information that the user wants in a few seconds. For example, computer dictionaries are available and the contents of this software version are the same as that of the printed dictionary.
5. Versatility: Computers can perform activities ranging from simple calculation like arithmetic calculation, to a complex calculation like launching a missile, which it makes a computer a versatile machine. some application area of computers like a business, bank medical diagnosis, science and technology, communication and astronomy, so it is a versatile machine.
6. Diligence:Diligence means being constant and determined in effort and application. The computer can perform the repetitive task without being a bore and it never gets tired. It can work continuously for several hour or day without getting bored and tired. Unlike human beings, a computer is free from tiredness, weakness, lack of concentration and monotony. Computers can perform activities ranging from simple calculation like arithmetic calculation, to a complex calculation like launching a missile, which it makes a computer a versatile machine.
7. Automation: A computer is an automatic machine, capable of functioning automatically once they are an appropriate set of instruction and data provided to the computer. Once the task is initiated on a computer it can proceed continuously. The computer can be programmed to perform a series of a task involving multiple programs. Computers are capable of these levels of automation if the instruction is provided correctly.
8. Reliability: Computers are used widely as they are reliable. The computer never gives the wrong result as long as the input is given correctly. The probability of error in the computer is negligible. A Huge amount of verities of data like monetary transaction, banking account, personal information is stored in a computer with the strong reliability to the computer.
   The computer has become an integral part of our lives and is helping us in improving the standard living, enhancing the quality products, providing better healthcare, assisting in teaching and learning and other however computer have many limitations like lack of intelligence, lack of reasoning capabilities and other.

Advantages and Disadvantages of Computer

Advantages:

1. The computer can perform complex operations in a short time.
2. The computer can process a large volume of data.
3. Computer can work continuously for a long time.
4. A single computer can perform multiple tasks such as watching a movie, playing games, listening to songs, and others.
5. The computer does not make mistakes.
6. Computer increases the curricular performance of the student.

Disadvantages:

1. The computer does not have a brain and cannot decide for itself.
2. It does not have its own intelligence.
3. The computer does not have emotions and feelings.
4. It needs electricity to operate.
5. It cannot operate itself unless a human command is given.

The Application Areas of Computer

1. Banks: Banks provide online accounting facilities, including current balances, deposits, overdrafts, interest charges, shares, and trustee records.
2. Engineering: Computers are widely used in engineering purposes, including Computer-Aided Design (CAD).
3. Medicine: Computers have become an important part of hospitals, labs, and dispensaries for patient records and diagnostic purposes.
4. Education: Computers are used in education for Computer-Based Education (CBE) and student performance analysis.
5. Ticketing: Online ticket booking for transportation and entertainment.
6. Defense: Computers are used in various military applications, including missile control and communication.
7. Business: Computers are integral in business organizations for various tasks such as payroll calculations and financial forecasting.
8. Government: Computers play a role in government functions, including budgeting and weather forecasting.
9. Desktop Publishing: Computers are used for desktop publishing, layout design, animation, and more.
10. Communication: Computers facilitate communication through email, chat, FTP, and more.

History of Computer

Evolution of computer is a study of past development of computer i.e. it is meant by the gradual improvements of accuracy, speed and efficiency of computers through generations, whereas generations of computers may be defined as the development of computer in an average period of time in which old computer technology may be replaced by newer technology.

Ancient people lived on the earth for centuries without counting. Then, they started to count their ten figures. It became so difficult to live and to remember anything. These phenomena were gradually replaced by the use of stones, counting notches on sticks or marks on walls. The different generations are described below which has helped the humans for keeping records with the passing of time.

1. The Mechanical Era (Zeroth generation)

   The calculator of this age was developed by using mechanical components like wood, metal, stone, bone, etc. It was used for simple mathematical calculations. Some of the popular calculations used in this age are:

   1. Abacus

   In ancient period, it was used to calculate mathematical calculation. It was used for performing simple calculation like counting, addition, subtraction and multiplication of number. An abacus consists of a rectangular frame carrying a number of wooden rods. Mid-bar divides each of these rods in top unequal -upper and lower parts.

   The upper part is called heaven, whereas lower part is called earth. The heaven consists of two beads, whereas the earth part consists of five beads to each rod. The value of bead on heaven part is five and earth is one. Each abacus consists of nine or eleven or thirteen rods.

   2. John Napier (1550-1617 AD)

   The Scottish mathematician John Napier first published the table of logarithms in 1614 AD. It was very used and consists of a large number of calculations.

   He invented bone rods and used bones to demonstrate by subtracting and multiplication by addition according to his principle. These are made of strips of bones on which numbers were carved and painted that`s why it is also called Napier's bone.

   3. Slide Rule (1575-1660AD)

   Based on the principle of John Napier, William Oughterd, an English mathematician, invented a machine called Slide Rule in 1620 A.D. It had 2 rulers engraved with the numbers and people could use it for faster multiplication and division also. He used the principal of bones and logarithms. A rule consists of two graduated scales, one of which slips upon other. It is devised in such a way that suitable alignment of one scale against the other makes it possible to find products and quotient of any numbers.

   4. Blaise Pascal (1623-1662AD)

   Pascaline was invented by Blaise Pascal in 1642 AD. He was the Famous French mathematician and philosopher. He invented the device to help his father in his profession. It had some cogs and gears rotating in complement to each other and it could do addition and subtraction up to 8 digits.

   Multiplication and division was done by repeating addition and subtraction respectively.

   Later computer programming language was called “Pascal” to honor him for his contribution in the development of computer.

   5. Jacquard Loom (1752-1834 AD)

   The French man, Joseph Marie Jacquard, was a textile manufacturer who invented a mechanism for automated weaving clothes for the textile industry at Lyon, in 1802 AD. This machine was used to automatically control weaving looms to facilitate the production of weaving cloth with complex patterns.

   Charles Babbage (1791-1871 AD)

   Charles Babbage was born in 1791 AD in United Kingdom. He was a professor of mathematics at Cambridge University. He discovered the principle for the construction of general purpose fully programmable automatic mechanical computer on which the modern electronic computers are based. So, Babbage is known as “father of computer”.

   1. Difference Engine

      Difference engine was the first invention of Charles Babbage and it was powered by steam. In 1822 AD he persuaded the British government to finance his design to build a machine that would calculate tables for logarithms. It was fully automatic for the mathematical calculations as well as printing output tables. It was controlled by a fixed instruction program that executed only in precise linear sequence.

   2. Analytical Engine

      Charles Babbage designed another machine called Analytical engine in 1833 AD after 10 years of inventing of Difference Engine but unfortunately he was unable to complete it. Analytical engine was an interconnected maze of gears, cams and shafts and powered by steam. This machine was capable for calculating up to 20 decimals at about 60 additions per minute, could store information, make decision and carry out instructions based on its decision.

   Lady Augusta Ada Lovelace (1515-1852 AD)

   The English intelligent and independent-minded woman, Lady Augusta, was a daughter of English poet Lord Byron and a very Great follower, assistant of Charles Babbage. Lady documents Babbage`s work and writes programs for Babbage.

   This plan is now regarded as the first computer program. That`s why, she was considered the first computer programmer and a software language developed by the US Defense Department, was named Ada in her honor.

   6. Tabulating Machine (1860-1929 AD)

   An American Inventor, Herman Hollerith, also applied the Jacquard loom concept in computing and applies for patents for an automatic punch-card tabulating machine. In 1886 A.D. he invented a machine knows as “Tabulating Machine ". This device could process on the punch cards and perform census calculating faster than ever before. He establish his own company called Tabulating Machine Company (TMC), later TMC was integrated with other companies and established IBM in 1923 AD.

   George Boole

   He was one of the greatest English Mathematician who contributed greatly to the study of symbolic logic during the mid-19th century. He was very famous for the discovery of mathematic logic called Boolean Algebra. It was the foundation of the modern electronic computer architecture by using 0 or 1 for the electric circuit. Since switching mechanisms at the time could only produce two actions ‘on’ and ‘off’, Boolean algebra provided engineers a medium to communicate with their computers.

2. The Electro-Mechanical Era

   The calculator of this age was developed by using mechanical and electronic component vacuum tube.

   Successful general-purpose mechanical computers were built, in the 1930s.

   1. The Mark I Computer (1937 - 1944)

      Based on the principle of Charles Babbage, Howard Aiken developed an electro-mechanical computer in 1973 AD. It was also called IBMASCC (IBM Automatic Sequence Control Calculator).

      It was complex in design because it contained 7,50,000 parts and was strung with about 500 miles of wires. It was very huge in size and its dimension was 50 feet long, 8 feet high and 3 feet in wides. Its weight was about 32 tons and it had 18,000 vacuum tubes. It consumed a lot of electricity and generated much more heat.

   2. The Mark II

      The Mark II was constructed with high-speed electromagnetic relays instead of electro-mechanical counters used in the Mark I, making it much faster. A unique feature of the Mark II is that it had built-in hardware for several functions such as the reciprocal, square root, logarithm, exponential, and some trigonometric functions.

   3. The Atanasoff-Berry Computer (1939 - 1942)

      In 1939, John Vincent Atanasoff and Clifford Berry designed Atanasoff-Berry computer or ABC solving systems of mathematical simultaneous equations. It used 18000 valves and other 45 valves for internal logic and capacitors for storage of electrical charges.

      It used punch cards as input and output operation i.e secondary. It is considered as the first computing machine which introduced the idea of binary arithmetic, regenerative memory and logic circuits.

3. The Electronic Computer Era

   The computers of this age are developed by using electronic components like a vacuum tube, transistors IC, VLSI, etc. These computers are smaller, faster and more reliable.

   1. The ENIAC (1943-1946)

      In 1946, John W. Mauchly and J.presper Eckert constructed ENIAC (Electronic Numerical Integrated and Calculator), at the Moore School of Engineering of the University of Pennsylvania. USA ENIAC was the first popular general-purpose electronic computer. John Von Neumann was the consultant of the ENIAC project.

      It was a very large machine weighing about 30 tons and containing about 17,468 vacuum tubes, 70,000 resistors, 5 million soldered joints and it consumed 160 kilowatts. It could do 5,000 additions and 300 multiplications per second.

   John Von Neumann (1903-1975 AD)

   The Hungarian Mathematician, John gave an idea of stored program computer in the sense that the program is stored internally in the main memory of the computer along with its associated data, in 1945. So, he is called the "Father of Stored Program". Before that, program required for the computer were integrated and written permanently in chips. So, modification of the program was not possible. But, after Neumann, such programs were stored on a computer in some storage media, so modification was easy and flexible.

   2. EDSAC (Electronic Delay Storage Automatic Computer)

      EDSAC stands for electronic delay storage automatic computer which was made by Maurice Wilkes in 1949 AD by applying John Von Neumann’s stored program technique. EDSAC contained 3,000 vacuum tubes and used mercury delay lines for memory. Programs were input using paper tape and output results were passed to the teleprinter.

   3. The EDVAC (1946-1952)

      EDVAC (Electronic Discrete Variable Automatic Computer) was developed by J.P Eckert, and J.W Mauchly in 1952 AD. It was also based on John Von Neumann’s stored program technique. The EDVAC is used for the Ballistics Research Laboratory of the US Army.

      The EDVAC was a binary serial computer with automatic addition, subtraction, multiplication, programmed division, and automatic checking with an ultrasonic serial memory.

   4. The UNIVAC (1951)

      UNIVAC (Universal Automatic Computer) was developed by J.P.Eckert and J. Mauchly in 1951. It was the first general-purpose digital computer made for business and administrative use. It was designed to handle both numeric and textual information. Before this, all the computers were either used for defense or census. It was 8 feet high, 15 feet long, and weight was about 15 tons.

Generations of Computers

Computer generations classification is mainly based on the basic devices used. Also, the considerations are the architecture, languages, modes of operation, etc. The function performed by the computer and the speed of their operations have been changing since the old days to the most modern computer. Based on the period of development and the features incorporated, the computers are classified into different generations- First generation to Fifth generation. This is called the computer generation.

The classification and time periods are given below:

1. First Generation Computer (1945-1956)

   The computers during the period 1945 to 1955 are regarded as the First Generation of Computers. The first generation computers used vacuum tubes for electronic circuits and magnetic drums for memory. The vacuum tube was first developed by Lee Deforest in 1908.

   • Vacuum Tube

   A vacuum tube is a hollow glass cylinder containing a positive electrode and a negative electrode between which is conducted in a full or partial vacuum. A grid between these electrodes controls the flow of electricity.

   The vacuum tube were predominantly used in electronic devices such as TVs, radios and computers.

   Features of Vaccum Tubes
   1. Technology used: vacuum tube
   2. Machines languages were used to instruct the computer.
   3. Magnetic core memory was used as primary memory.
   4. Electrostatic tubes, Paper tape, punch card, magnetic tape
   5. Punched card, printing devices were used for input/output operations and store the result.
   6. It occupies very large space, slow processing, inefficient and unreliable due to low accuracy.
   7. Power consumption was very high and it generated much heat.
   8. It could only perform straight forward simple numerical calculation.
   9. Computer used to be much expensive.
   Example of First-Generation computer: ENIAC, UNIVAC, EDVAC, and EDSAC.
2. Second Generation Computer (1957-1963)

   The computer during the period 1956 to 1963 are regarded as the Second generation Computers. In the second generation computer, the vacuum tubes were replaced by transistors. They used transistors as the electronic circuits. The transistors made the second generation computers smaller, faster, cheaper than the first generation computers.

   • Transistor

   Transistor is derived from the two words “transfer” and “register” and it is the device which is made of three terminal semi-conductor material that amplifies the electric signal.

   Feature of Transistor
   1. Technology used: Transistor
   2. Operating speed was in terms of a microsecond.
   3. Assembly language and machines independent language such as COBOL (Common Business Oriented Language) and FORTRAN (Formula Translation) were introduced the size of the computer.
   4. Magnetic core memory was used as primary memory.
   5. Magnetic drum and magnetic tape were used as secondary memory.
   6. Power required to operate them was low.
   7. It could perform scientific calculation such as solving differential equations.
   8. Storage capacity and use of computers are increased.
   Example of Second-Generation computer: IBM 1620, IBM 7094, CDC 1604, CDC 3600, UNIVAC 1108.
3. Third Generation Computer (1964-1971)

   The computer during the period 1964 to 1971 are regarded as the Third generation Computers. They used Integrated Circuit (IC) as electronic circuit. IC consist of consist of a large number of electronic components placed on a single silicon chip. The IC was developed by Jack Kilby and Robert Noyce in 1958. The IC made the third generation computer more smaller in size, reliable, faster, easy to operate and less expensive than the previous generation.

   • Integrated Circuit

   An integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. An integrated circuit, commonly referred to as an IC, is a microprocessor array of electronic circuits.

   Features of the third-generation computers are:
   1. The technology used: IC (Integrated Circuit).
   2. Transistors were replaced by IC in their electronic circuitry.
   3. High-level languages like FORTAN, BASIC, and others were used to develop programs.
   4. Semiconductor memory like RAM and ROM were used as primary memory.
   5. Monitor and keyboard were introduced for data input and output, respectively.
   6. Multiprogramming facility was developed.
   7. The computer was used in census calculation, military, banks, and industries.
   8. Size, cost, power requirement, and heat generation decreased.
   9. Processing speed and storage capacity of the computer increased.

   The example of third-generation computers includes IBM-360 series, ICL-900 series, and Honeywell 200 series.

4. Fourth Generation Computer (1972 onward)

   The computer during the period 1972 to present are regarded as the Fourth generation Computers. All modern computers we use today are fourth generation computers. They use VLSI and ULSI are called Microprocessor chips for electronic circuit. It was developed by Intel Corporation USA in 1971.

   • Microprocessor

   A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together.

   Features of the fourth-generation computers are:
   1. Technology in use: VLSI is introduced and used Microprocessor-based technology.
   2. Problem-oriented fourth generation language (4GL) is used to develop the program.
   3. Semiconductor like RAM, ROM, and cache memory is used as primary memory.
   4. Magnetic disks like hard disk, optical disk (CD, DVD), Blu-ray disk, flash memory (memory chip, pen drive) are used as secondary memory.
   5. E-mail, Internet, and mobile communication are developed.
   6. Advanced, user-friendly, web page software is developed.
   7. Size, cost, power requirement, heat generation decreased compared to the previous generation.
   8. Operating speed, storage capacity, use of computer increased compared to the previous generation.

   The example of the fourth-generation computer includes IBM-PC, HP laptops, Mac notebooks, etc.

5. Fifth Generation Computer (Present and future)

   The aim is to bring machines with genuine IQ, the ability to reason logically and with real knowledge of the word. Thus, this computer will be totally different, totally novel and totally new than last four generations of computer.

   Fifth generation computer was based on Artificial Intelligence (AI) and that is still developing process, but not yet a reality i.e this computer is incomplete. The scientists are working on it still.

   These computers will be able to converse with people and will be able to mimic human sense, manual skills, and intelligence.

   Features of the fifth-generation computers are:
   1. Technology to be used: These machines will incorporate Bio-chip and VVLSI (Very Very Large-Scale Integration) or Ultra-Large-Scale Integration (ULSI).
   2. The computer will have Artificial Intelligence (AI).
   3. Natural language will be used to develop programs.
   4. The computer will have parallel processing in full fledge.
   5. These aims are to solve highly complex problems, which require great intelligence and expertise when solved by people.
   6. Quantum computation, molecular, and nanotechnology will be used completely.

   Example of the fifth-generation computer: IBM-WATSON, Google car, etc.

Classification of Computer (On the basis of Size)

Computers are classified into four categories based on their size, cost, and performance. They are:

1. Super Computer
2. Mainframe Computer
3. Mini Computer
4. Micro Computer

1. Super Computer:

A supercomputer is a computer with a high level of performance as compared to a generalpurpose computer. The performance of a supercomputer is commonly measured in floatingpoint operations per second (FLOPS) instead of million instructions per second (MIPS). Additional research is being conducted in the United States, the European Union, Japan, and China to build faster, more powerful and technologically superior supercomputers.

Supercomputers play an important role in the field of computational science, and are used for a wide range of computationally intensive tasks in various fields, including quantum mechanics, weather forecasting, climate research, oil and gas exploration, molecular modeling, airplane and spacecraft aerodynamics, the detonation of nuclear weapons, and nuclear fusion. Examples: Titan, IBM Summit, Fugaku, PARAM, Deep Blue etc.

2. Mainframe Computer:

Mainframe computers are powerful multi-user computers capable of supporting thousands of users simultaneously. It is also large in size. This computer has slower processing speed than a super computer but faster than a mini and micro-computer. It is designed for large-scale data processing and a huge amount of data storage. They are used in a big organization such as bank, insurance companies, airlines, railway reservation system, e-mail service providers, web hosting, etc.

In a mainframe, each user accesses the mainframe’s resources through a device called a terminal. Their terminals are attached to the mainframes to perform the different types of task.

Dumb terminal and intelligent terminal are the two kinds of terminals. A dumb terminal does not have its own CPU and storage devices. This type of terminal uses the CPU and storage of device of mainframe system. Specially, a dumb terminal is consist of input and output devices. The intelligent terminal has its own processor and can perform processing jobs.

Examples:IBM System z9, IBM System z10, IBM zEnterprise System, IBM z13, IBM z14, IBM z15, etc.

Use: Industries, Banking, Insurance companies, Airlines, Air Traffic Control, Bulk data processing etc.

3. Mini Computer:

Minicomputer is a multi-user computer having lower processing speed and are cheaper than mainframe computer. Due to the smaller size and its cost compared to mainframe and a super computer, it got its name as a minicomputer. It is also known as midrange computer. Minicomputer can handle more input and output than a micro-computer. Minicomputers are commonly used as server in network (hundreds of personal computers can be connected to the network) or a data processing system in a medium organization, medium sized business, education, industries, universities, banks and many other government departments. Although some minicomputers are designed for single user to handle sophisticated design tasks.

Example: PDP8, PDP 11, IBM 8000 series, VAX 7500 etc.
4. Micro Computer:

A computer which is based on a microprocessor is called microcomputer. They are small and single user computer. This computer has a keyboard for entering data, a monitor for displaying and a storage device for storing the data. It requires less area compared to other computers.

This computer consists of central processing unit and a single chip. It is mainly used in office, school, house, shop, etc. The smallest of this category are a laptop, notebook, palmtop and PDA. IBM PC, Apple/Macintosh, etc. are the examples of the microcomputer. The microcomputer is categorized as a non-portable and portable category.

Some of the examples of microcomputer are described below:

1. Desktop

The desktop computer is the kind of personal computer (PC), which is a common type of computer used by many people today. They are a non-portable computer.

The term “desktop computer” means the concept of such a computer actually sitting on top of a desk. A desktop computer typically comes in several units that are connected together during installation that may be processor, the display monitor and input devices. Today’s almost all desktop computer include built in network interface card, a DVD-RW drive and large size magnetic storage drive.

2. Laptop

A ‘laptop’ computer is a light, compact and portable PC. It contains a rechargeable battery. They also contain a built-in LCD monitor. It is a portable computer.

To make them as portable as possible; most laptops try to avoid any sort of cable or wire. In laptop, instead of a mouse, a touchpad is used. Instead of wired connection to a network or printer, ‘wireless’ radio connection are used. Laptops are also sometime called Notebooks.

3. Ultrabook

Ultrabook is a category of thin and light laptop computers design to full fill the gap between tablets and notebook PCs. Ultrabook provides more user friendly features such as faster processor, additional RAM, better storage, screen size as well as long battery life.

4. Handheld

A handheld computer is a kind of portable computer that is intended to be held and used in a hand. A handheld computer is becoming more and more common in modern society. This computer includes various kinds of PDA (Personal Digital Assistant) computers, such as those running palm OS or windows mobile. Nowadays, mobile phones have slowly replaced by smartphones and similar handhelds with mobile phone capabilities.

Those phones which contains the running of Google Android, windows mobile and also the iPhone are the handheld computer which has the function of mobile phones.

5. Smartphone

A smart phone is a mobile phone that includes advanced functionality beyond making phone calls and sending text message. Most smart phones have the capability to display photos, play videos, surf the web, check and sent e-mail etc. modern smart phones can run third party applications which provides limitless functionality.

Mobile Computing

Mobile computing is the form of human-computer interaction by which a computer is expected to be transported during normal usages. Mobile computing has three aspects: mobile communication, mobile hardware and mobile software.

Mobile computing is a generic term describing one's ability to use technology while moving, as opposed to portable which is the only particle for use while deployed in a stationary configuration. A mobile computing device is created using mobile components, such as mobile hardware and software.

Mobile computing devices are portable devices capable of operating, executing, providing services and applications to a computing device. It is a computing device used in transit. Users can access data and information from wherever they are.

Many types of mobile computers have been introduced since the 1990's including wearable computer, PDA, enterprise digital assistant, smart phone, UMPC (Ultra-mobile PC), Tablet PC.

Characteristics of mobile computing

1. It is a portable device that you can carry during mobility.
2. It has limited processing and storage capability.
3. It includes mobile communication, mobile hardware, and mobile software.
4. It contains on-screen or virtual keyboard for proving text inputs. However, an external keyboard can be connected by using USB port, infrared or Bluetooth.
5. It contains the camera, speaker, and microphone etc.
6. It contains handwriting recognizing software.
7. It has wireless connectivity such as Bluetooth, Wi-Fi, to connect the Internet or with other computing devices as well as the wired connection through the USB port.
8. It can be used for cloud computing and remote access.
9. It uses the mobile computing operating system such as Android, iOS, Windows Mobile OS.
10. It can include GPS (Global Positioning System) receiver for navigation.

Advantages

1. Increase in Productivity - Mobile devices can be used out in the field of various companies, therefore reducing the time and cost for clients and themselves.
2. Entertainment - Mobile devices can be used for entertainment purposes, for personal and even for presentations to people and clients.
3. Portability - This would be one of the main advantages of mobile computing; you are not restricted to one location in order for you to get jobs done or even access email on the go.
4. Cloud Computing - This service is available for saving documents on an online server and being able to access them anytime and anywhere when you have a connection to the internet and can access these files on several mobile devices or even PCs at home.
5. Quick Service - We can sell a product or give service in quicker time by using mobile computing.
6. Social Interactivity - It is a very useful tool for social interactivity that allows for data sharing and collaboration between users.

Disadvantages

1. Quality of Connectivity - As one of the disadvantages, mobile devices will need either WiFi connectivity or mobile network connectivity such as GPRS, 3G, and in some countries even 4G connectivity. That is why this is a disadvantage because if you are not near any of these connections, your access to the internet is very limited.
2. Security Concerns - Mobile VPNs are unsafe to connect to, and also syncing devices might also lead to security concerns.
3. Power Consumption - Due to the use of batteries in these devices, they do not tend to last long. If in a situation where there is no source of power for charging, then that will certainly be a letdown.
4. Human Interface with Device - These are still uncommon, screens are often too small. Keyboards are impractical, especially one-handed.