Introduction and Evolution of Computer

Introduction and Evolution of Computer 

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem. An important class of computer operations on some computing platforms is the accepting of input from human operators and the output of results formatted for human consumption. The interface between the computer and the human operator is known as the user interface.
Conventionally a computer consists of some form of memory, at least one element that carries out arithmetic and logic operations, and a sequencing and control unit that can change the order of operations based on the information that is stored. Peripheral devices allow information to be entered from an external source, and allow the results of operations to be sent out.
A computer's processing unit executes series of instructions that make it read, manipulate and then store data. Conditional instructions change the sequence of instructions as a function of the current state of the machine or its environment.
The first electronic digital computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs). In this era mechanical analog computers were used for military applications.
Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Simple computers are small enough to fit into mobile devices, and mobile computers can be powered by small batteries. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from mp3 players to fighter aircraft and from toys to industrial robots are the most numerous.

General Functions of Computer
Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations.

A computer has four functions:
a. accepts data Input
b. processes data
c. produces output
d. stores results

Input (Data):
Input is the raw information entered into a computer from the input devices. It is the collection of letters, numbers, images etc.
Process is the operation of data as per given instruction. It is totally internal process of the computer system.
Output is the processed data given by computer after data processing. Output is also called as Result. We can save these results in the storage devices for the future use.
Computer data storage, often called storage or memory, refers to computer components andrecording media that retain digital data. Data storage is a core function and fundamental component of computers.

Computer System
All of the components of a computer system can be summarized with the simple equations.
Hardware = Internal Devices + Peripheral Devices
The hardware are the parts of the computer itself including the Central Processing Unit (CPU) and related microchips and micro-circuitry, keyboards,monitors, case and drives (hard, CD, DVD, floppy, optical, tape, etc...). Other extra parts called peripheral components or devices include mouse, printers,modems, scanners, digital cameras and cards (sound, colour, video) etc... Together they are often referred to as a personal computer.
All physical parts of the computer (or everything that we can touch) are known as Hardware.
Software = Programs
The software is the information that the computer uses to get the job done. Software needs to be accessed before it can be used. There are many terms used for the process of accessing software including running, executing, starting up,opening, and others.
Computer programs allow users to complete tasks. A program can also be referred to as an application and the two words are used interchangeably.
Software gives "intelligence" to the computer.

USER = Person, who operates computer.
A user is an agent, either a human agent (end-user) or software agent, who uses a computer or network service. Users are also widely characterized as the class of people that use a system without complete technical expertise required to understand the system fully. Such users are also divided into users and power users. Both are terms of degradation but the latter connotes a "know-it-all" attitude.
In projects in which the actor of the system is another system or a software agent, it is quite possible that there is no end-user for the system. In this case, the end-users for the system would be indirect end-users.

Speed, accuracy, diligence, storage capability and versatility are some of the key characteristics of a com-
puter. A brief overview of these characteristics are—
Speed The computer can process data very fast, at the rate of millions of instructions per second.
Some calculations that would have taken hours and days to complete otherwise, can be completed
in a few seconds using the computer. For example, calculation and generation of salary slips of
thousands of employees of an organization, weather forecasting that requires analysis of a large
amount of data related to temperature, pressure and humidity of various places, etc.
Accuracy Computer provides a high degree of accuracy. For example, the computer can accu-
rately give the result of division of any two numbers up to 10 decimal places.
Diligence When used for a longer period of time, the computer does not get tired or fatigued.
It can perform long and complex calculations with the same speed and accuracy from the start till
the end.
Storage Capability Large volumes of data and information can be stored in the computer and
also retrieved whenever required. A limited amount of data can be stored, temporarily, in the
primary memory. Secondary storage devices like fl oppy disk and compact disk can store a large
amount of data permanently.
Versatility Computer is versatile in nature. It can perform different types of tasks with the same
ease. At one moment you can use the computer to prepare a letter document and in the next
moment you may play music or print a document.
Computers have several limitations too. Computer can only perform tasks that it has been programmed
to do. Computer cannot do any work without instructions from the user. It executes instructions as speci-
fi ed by the user and does not take its own decisions.

Application of Computers
Computers have proliferated into various areas of our lives. For a user, computer is a tool that provides the desired information, whenever needed. You may use computer to get information about the reservation of tickets (railways, airplanes and cinema halls), books in a library, medical history of a person, a place in a map, or the dictionary meaning of a word.  The information may be presented to you in the form of text, images, video clips, etc. Some of the application areas of the computer are listed below:
Education Computers are extensively used, as a tool and as an aid, for imparting education.
Educators use computers to prepare notes and presentations of their lectures. Computers are used to develop computer-based training packages, to provide distance education using the e-learning software, and to conduct online examinations. Researchers use computers to get easy access to conference and journal details and to get global access to the research material.
Entertainment Computers have had a major impact on the entertainment industry. The user can download and view movies, play games, chat, book tickets for cinema halls, use multimedia for making movies, incorporate visual and sound effects using computers, etc. The users can also listen to music, download and share music, create music using computers, etc.
Sports A computer can be used to watch a game, view the scores, improve the game, play games (like chess, etc.) and create games. They are also used for the purposes of training players.
Advertising Computer is a powerful advertising media. Advertisement can be displayed on different websites, electronic-mails can be sent and reviews of a product by different customers can be
posted. Computers are also used to create an advertisement using the visual and the sound effects.
For the advertisers, computer is a medium via which the advertisements can be viewed globally.
Web advertising has become a signifi cant factor in the marketing plans of almost all companies. In
fact, the business model of Google is mainly dependent on web advertising for generating revenues.
Medicine Medical researchers and practitioners use computers to access information about
the advances in medical research or to take opinion of doctors globally. The medical history of
patients is stored in the computers. Computers are also an integral part of various kinds of sophis-
ticated medical equipments like ultrasound machine, CAT scan machine, MRI scan machine, etc.
 Computers also provide assistance to the medical surgeons during critical surgery operations like
laparoscopic operations, etc.
Science and Engineering Scientists and engineers use computers for performing complex sci-
entifi c calculations, for designing and making drawings (CAD/CAM applications) and also for
simulating and testing the designs. Computers are used for storing the complex data, performing
complex calculations and for visualizing 3-dimensional objects. Complex scientifi c applications
like the launch of the rockets, space exploration, etc., are not possible without the computers.
Government The government uses computers to manage its own operations and also for e-
governance. The websites of the different government departments provide information to the
users. Computers are used for the fi ling of income tax return, paying taxes, online submission of
water and electricity bills, for the access of land record details, etc.
Home Computers have now become an integral part of home equipment. At home, people use
computers to play games, to maintain the home accounts, for communicating with friends and relatives via Internet, for paying bills, for education and learning, etc. Microprocessors are embedded in house hold utilities like, washing machines, TVs, food processors, home theatres, security devices, etc. The list of applications of computers is so long that it is not possible to discuss all of them here. In addition to the applications of the computers discussed above, computers have also proliferated into areas like banks, investments, stock trading, accounting, ticket reservation, military operations, meteorological predictions, social networking, business organizations, police department, video conferencing, tele-presence, book publishing, web newspapers, and information sharing.

History of computer science

The history of computer science began long before the modern discipline of computer science that emerged in the twentieth century, and hinted at in the centuries prior. The progression, from mechanical inventions and mathematical theories towards the modern concepts and machines, formed a major academic field and the basis of a massive worldwide industry.
Mechanical computers:
A mechanical computer is built from mechanical components such as levers and gears, rather than electronic components. The most common examples are adding machines and mechanical counters, which use the turning of gears to increment output displays. More complex examples can carry out multiplication and division, and even differential analysis.

The abacus, also called a counting frame, is a calculating tool used primarily in parts of Asia for performing arithmetic processes. Today, abaci are often constructed as a bamboo frame with beads sliding on wires, but originally they were beans or stones moved in grooves in sand or on tablets of wood, stone, or metal. The abacus was in use centuries before the adoption of the written modern numeral system and is still widely used by merchants, traders and clerks in Asia, Africa, and elsewhere. The user of an abacus is called an abacist.

Napier’s Bones
Napier's bones is an abacus created by John Napier for calculation of products and quotients of numbers that was based on Arab mathematics and lattice multiplication. The abacus consists of a board with a rim; the user places Napier's rods in the rim to conduct multiplication or division. The board's left edge is divided into 9 squares, holding the numbers 1 to 9. The Napier's rods consist of strips of wood, metal or heavy cardboard. Napier's bones are three dimensional, square in cross section, with four different rods engraved on each one. A set of such bones might be enclosed in a convenient carrying case.
A rod's surface comprises 9 squares, and each square, except for the top one, comprises two halves divided by a diagonal line. The first square of each rod holds a single digit, and the other squares hold this number's double, triple, quadruple, quintuple, and so on until the last square contains nine times the number in the top square. The digits of each product are written one to each side of the diagonal; numbers less than 10 occupy the lower triangle, with a zero in the top half. A set consists of 10 rods corresponding to digits 0 to 9. The rod 0, although it may look unnecessary, is obviously still needed for multipliers or multiplicands having 0 in them.

Slide rule
The slide rule is a mechanical computer. The slide rule is used primarily for multiplication and division, and also for functions such as roots, logarithms and trigonometry, but is not normally used for addition or subtraction.
Slide rules come in a diverse range of styles and generally appear in a linear or circular form with a standardized set of markings (scales) essential to performing mathematical computations. Slide rules manufactured for specialized fields such as aviation or finance typically feature additional scales that aid in calculations common to that field.
William Oughtred and others developed the slide rule in the 17th century based on the emerging work on logarithms by John Napier. Before the advent of the pocket calculator, it was the most commonly used calculation tool in science and engineering. The use of slide rules continued to grow through the 1950s and 1960s even as digital computing devices were being gradually introduced; but around 1974 the electronic scientific calculator made it largely obsolete and most suppliers left the business.


Pascal's calculator

Blaise Pascal invented the mechanical calculator in 1642. He conceived the idea while trying to help his father who had been assigned the task of reorganizing the tax revenues of the French province of Haute-Normandie ; first called Arithmetic Machine, Pascal's Calculator and later Pascaline, it could add and subtract directly and multiply and divide by repetition.
Pascal went through 50 prototypes before presenting his first machine to the public in 1645. He dedicated it to Pierre Séguier, the chancellor of France at the time. He built around twenty more machines during the next decade, often improving on his original design. Nine machines have survived the centuries, most of them being on display in European museums. In 1649 a royal privilege, signed by Louis XIV of France, gave him the exclusivity of the design and manufacturing of calculating machines in France.

Stepped Reckoner

The Step Reckoner (or Stepped Reckoner) was a digital mechanical calculator invented by German mathematician Gottfried Wilhelm Leibniz around 1672 and completed in 1694. The name comes from the translation of the German term for its operating mechanism; staffelwalze meaning 'stepped drum'. It was the first calculator that could perform all four arithmetic operations: addition, subtraction, multiplication and division.
Its intricate precision gearwork, however, was somewhat beyond the fabrication technology of the time; mechanical problems, in addition to a design flaw in the carry mechanism, prevented the machines from working reliably.

Jacquard loom
The Jacquard loom is a mechanical loom, invented by Joseph Marie Jacquard in 1801, that simplifies the process of manufacturing textiles with complex patterns such as brocade, damask and matelasse. The loom is controlled by punched cards with punched holes, each row of which corresponds to one row of the design. Multiple rows of holes are punched on each card and the many cards that compose the design of the textile are strung together in order. It is based on earlier inventions by the Frenchmen Basile Bouchon (1725), Jean Baptiste Falcon (1728) and Jacques Vaucanson (1740).

Charles Babbage's Difference engine
A difference engine is an automatic, mechanical calculator designed to tabulate polynomial functions. The name derives from the method of divided differences, a way to interpolate or tabulate functions by using a small set of polynomial coefficients. Both logarithmic and trigonometric functions, functions commonly used by both navigators and scientists, can be approximated by polynomials, so a difference engine can compute many useful sets of numbers. The historical difficulty in producing error free tables by teams of mathematicians and human "computers" spurred Charles Babbage's desire to build a mechanism to automate the process.

Analytical Engine
The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, a design for a mechanical calculator. The Analytical Engine incorporated an arithmetical unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first Turing-complete design for a general-purpose computer.

Charles Babbage (1791-1871) the Father of Computers
Charles Babbage is recognized today as the Father of Computers because his impressive designs for the Difference Engine and Analytical Engine foreshadowed the invention of the modern electronic digital computer.  He led a fascinating life, as did all the folks involved in the history of computers. He also invented the cowcatcher, dynamometer, standard railroad gauge, uniform postal rates, occulting lights for lighthouses, Greenwich time signals, heliograph opthalmoscope.

Lady Augusta Ada Countess of Lovelace (First Computer Programmer)
Babbage owes a great debt to Lady Augusta Ada, Countess of Lovelace.  Daughter of the famous romantic poet, Lord Byron, she was a brilliant mathematician who helped Babbage in his work.  Above all, she documented his work, which Babbage never could bother to do.  As a result we know about Babbage at all.  Lady Augusta Ada also wrote programs to be run on Babbage’s machines.  For this, she is recognized as the first computer programmer. 

Electro-Mechanical Computer:
Census Tabulating Machine
Herman Hollerith Develop The tabulating machine. The tabulating machine was an electrical device designed to assist in summarizing information and, later, accounting. Invented by Herman Hollerith, the machine was developed to help process data for the 1890 U.S. Census. It spawned a larger class of devices known as unit record equipment and the data processing industry.

Herman Hollerith worked as a statistician for the U.S. Census Bureau in the 1880s and 1890s.  The U.S. Constitution requires a census count every ten years so that the membership of the House of Representatives will be proportional to the population of each state.  This is always a moving target, hence the ten year review of the current state of demographic affairs.  The 1880 census took seven years to process.  The end of the 19th/beginning of the 20th centuries was the period of highest rate of immigration to the United States.  Hollerith deduced,and it didn’t take a rocket scientist to conclude, that the next census would take longer than ten years, the results not available before the whole census counting thing had to start again.
So, as the saying goes, “necessity became the mother of invention” and Hollerith designed and built the Census Counting Machine illustrated here and in the next slide.  Punched cards (a la Jacquard looms) were used to collect the census data (the origin of the IBM punched cards) and the cards were fed into a sorting machine before being read by the census counting machine which recorded and tabulated the results.  Each card was laid on an open grid.  A matrix of wires was lowered onto the card and wherever there was a hole in the card, a wire fell through, making an electrical connection which triggered a count on the appropriate dial(s) in the face of the machine.  The 1890 census took just three months to process even though quite a bit more data was collected than ever before.
Hollerith was the first American associated with the history of computers.  As you might expect, he was also the first to make a bunch of money at it.  His company, the Tabulating Machine Company, became the Computer Tabulating Recording Company in 1913 after struggling in the market and merging with another company that produced a similar product.  The company hired a gentleman named Thomas J. Watson in 1918 who was primarily instrumental in turning the company around.  In 1924, the company was renamed International Business machines (IBM) Corporation.

Harvard Mark I
The IBM Automatic Sequence Controlled Calculator (ASCC), called the Mark I by Harvard University, was an electro-mechanical computer.
The electromechanical ASCC was devised by Howard H. Aiken, built at IBM and shipped to Harvard in February 1944. It began computations for the U.S. Navy Bureau of Ships in May and was officially presented to the university on August 7, 1944.
The ASCC was built from switches, relays, rotating shafts, and clutches. It used 765,000 components and hundreds of miles of wire, comprising a volume of 51 feet (16 m) in length, eight feet (2.4 m) in height, and two feet (~61 cm) deep. It had a weight of about 10,000 pounds (4500 kg). The basic calculating units had to be synchronized mechanically, so they were run by a 50-foot (~15.5 m) shaft driven by a five-horsepower (4 kW) electric motor. From the IBM Archives:
The Automatic Sequence Controlled Calculator (Harvard Mark I) was the first operating machine that could execute long computations automatically. A project conceived by Harvard University's Dr. Howard Aiken, the Mark I was built by IBM engineers in Endicott, N.Y.

The first computer bug
The lady is U.S. Rear Admiral Dr. Grace Murray Hopper, who worked with Howard Aiken from 1944 and used his machine for gunnery and ballistics calculation for the US Bureau of Ordnance’s Computation project.  One day, the program she was running gave incorrect results and, upon examination, a moth was found blocking one of the relays.  The bug was removed and the program performed to perfection.  Since then, a program error in a computer has been called a bug.

Electronic digital computers

The Turing Machine
The "Turing" machine was described by Alan Turing in 1936, who called it an "automatic-machine". The Turing machine is not intended as a practical computing technology, but rather as a hypothetical device representing a computing machine. Turing machines help computer scientists understand the limits of mechanical computation. A Turing machine is a device that manipulates symbols on a strip of tape according to a table of rules. Despite its simplicity, a Turing machine can be adapted to simulate the logic of any computer algorithm, and is particularly useful in explaining the functions of a CPU inside a computer.

Atanasoff–Berry Computer
The ABC was built by Dr. Atanasoff and graduate student Clifford Berry in the basement of the physics building at Iowa State College during 1939–42.
The Atanasoff–Berry Computer (ABC) was the first electronic digital computing device. Conceived in 1937, the machine was not programmable, being designed only to solve systems of linear equations. It was successfully tested in 1942. However, its intermediate result storage mechanism, a paper card writer/reader, was unreliable, and when inventor John Vincent Atanasoff left Iowa State College for World War II assignments, work on the machine was discontinued. The ABC pioneered important elements of modern computing, including binary arithmetic and electronic switching elements, but its special-purpose nature and lack of a changeable, stored program distinguish it from modern computers.

Colossus computer
Colossus was the world's first electronic, digital, programmable computer. Colossus and its successors were used by British codebreakers to help read encrypted German messages during World War II. They used thermionic valves (vacuum tubes) to perform the calculations.
Colossus was designed by engineer Tommy Flowers with input from Sidney Broadhurst, William Chandler, Allen Coombs and Harry Fensom. at the Post Office Research Station, Dollis Hill to solve a problem posed by mathematician Max Newman at Bletchley Park. The prototype, Colossus Mark 1, was shown to be working in December 1943 and was operational at Bletchley Park by February 1944. An improved Colossus Mark 2 first worked on 1 June 1944, just in time for the Normandy Landings. Ten Colossus computers were in use by the end of the war.
The Colossus computers were used to help decipher teleprinter messages which had been encrypted using the Lorenz SZ40/42 machine—British codebreakers referred to encrypted German teleprinter traffic as "Fish" and called the SZ40/42 machine and its traffic "Tunny". Colossus compared two data streams, counting each match based on a programmable Boolean function. The encrypted message was read at high speed from a paper tape. The other stream was generated internally, and was an electronic simulation of the Lorenz machine at various trial settings. If the match count for a setting was above a certain threshold, it would be sent as output to an electric typewriter.

ENIAC (Electronic Numerical Integrator And Computer)  was conceived and designed by John Mauchly and J. Presper Eckert of the University of Pennsylvania. The team of design engineers assisting the development included Robert F. Shaw (function tables), Jeffrey Chuan Chu (divider/square-rooter), Thomas Kite Sharpless (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer) and Jack Davis (accumulators).
ENIAC  was the first general-purpose electronic computer. It was a Turing-complete digital computer capable of being reprogrammed to solve a full range of computing problems.
ENIAC was designed to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory. When ENIAC was announced in 1946 it was heralded in the press as a "Giant Brain". It boasted speeds one thousand times faster than electro-mechanical machines, a leap in computing power that no single machine has since matched. This mathematical power, coupled with general-purpose programmability, excited scientists and industrialists. The inventors promoted the spread of these new ideas by conducting a series of lectures on computer architecture.

Generations of Computers

The history of computer development is often referred to in reference to the different generations of computing devices. A generation refers to the state of improvement in the product development process. This term is also used in the different advancements of new computer technology. With each new generation, the circuitry has gotten smaller and more advanced than the previous generation before it. As a result of the miniaturization, speed, power, and computer memory has proportionally increased. New discoveries are constantly being developed that affect the way we live, work and play.
Each generation of computers is characterized by major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable devices. Read about each generation and the developments that led to the current devices that we use today.


First Generation - 1940-1956: Vacuum Tubes

The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions.
First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts.
The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.


Second Generation (1956-1963) Transistors

Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late 1950s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output.
Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.

Third Generation (1964-1971) Integrated Circuits

The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers.
Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.

Fourth Generation (1971-Present) Microprocessors

The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer—from the central processing unit and memory to input/output controls—on a single chip.
In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.
As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.

Fifth Generation (Present and Beyond) Artificial Intelligence

Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.


Computer speed and Measurement Unit

Space measurement units

The size of device in computers does not reflect the space available to store data in it. There are larger devices that can store only a few data where as many tiny devices that stores unbelievable amount of data. Because how long, how thick etc cannot determine how much we can store inside, we need to find some other way to measure space.
Almost all of the computers use binary numbering systems (though there are some exceptions). Binary numbering system consists of only two digits – 0 and 1 to represent any quantity. 10 in binary is equal to the 2 and 100 to 5. We will be learning this numbering system after some days.
Everything in computers is represented in strings of binary numbers. For example capital A is interpreted by computer as 0100 0001 and B is 0100 0010. All characters, numbers, symbols, images, sounds, animations, videos and everything, yes everything is converted into suitable binary code to store in computer or process by computer.
So if there is any device that can store one binary digit (whether 0 or 1), its storage capacity is 1 bit. We’ve already learned that bit is the abbreviation of binary digit. Any device that has storage space to accommodate 5 binary digits has 5 bits space.
You require thousands and millions of bits for a file and expressing the space available in bits only is really inconvenient because it will be an extremely large number. So, we have larger units that represent a group of lower units.
A group of 4 binary digits is called a nibble (4 bits = 1 Nibble). Similarly a group of 8 bits is called a byte (1 byte = 8 bits).
As you have seen the example above, each character requires 8 bits which is 1 byte. So 1 character requires 1 byte space. Now, if you have a text file whose size is 32 bytes, it means there are 32 x 8 binary digits (0s and 1s) stored in it.
In the metric system 1000 lifts up the unit to the higher such as 1000 meter is 1 kilometer, 1000 liter is 1 kiloliter etc. In binary numbering system it is 1024 (=2 10) that converts to higher unit. Following table lists the different units and their values:

Space Measurement Units
0 or 1
1 Bit
4 bits
1 Nibble
8 bits
1 Byte
1024 bytes
1 Kilobytes (KB)
1024 Kilobytes
1 Megabyte (MB)
1024 Megabytes
1 Gigabytes (GB)
1024 Gigabytes
1 Terabytes (TB)
1024 Terabytes
1 Petabyte (PB)
1024 Petabytes
1 Exabyte (EB)

Speed Measurement Units

 speed is related to time. Computer can perform millions of tasks in one second. So to compare the speed of computer operation (execution of programs and instructions) we require some units that can represent a very small fraction of time. Following are the units used to indicate fraction of seconds:
Speed Measurement Units
1000 th of a second
1 Milliseconds (MS)
1000 th of a milliseconds
1 Microseconds (µs)
1000 th of a microseconds
1 Nanosecond (ns)
1000 th of a nanoseconds
1 Picoseconds (ps)
1000 th of a picoseconds
1 Femtoseconds (fs)

On the basis of size
The digital computers that are available nowadays vary in their sizes and types. The computers are broadly
classifi ed into four categories (Figure 1.8) based on their size and type—(1) Microcomputers, (2) Mini-
computers, (3) Mainframe computers, and (4) Supercomputer.

Figure:  Classification of computers based on size and type

Microcomputers are small, low-cost and single-user digital computer. They consist of CPU, input unit, output unit, storage unit and the software. Although microcomputers are stand-alone machines, they can be connected together to create a network of computers that can serve more than one user. IBM PC based on Pentium microprocessor and Apple Macintosh are some examples of microcomputers. Microcomputers include desktop computers, notebook computers or laptop, tablet computer, handheld computer, smart phones and notebook.
Desktop Computer or Personal Computer (PC) is the most common type of microcomputer. It is a stand-alone machine that can be placed on the desk. Externally, it consists of three units—key-board, monitor, and a system unit containing the CPU, memory, hard disk drive, etc. It is not very expensive and is suited to the needs of a single user at home, small business units, and organizations. Apple, Microsoft, HP, Dell and Lenovo are some of the PC manufacturers.
Notebook Computers or Laptop resemble a notebook. They are portable and have all the features of a desktop computer. The advantage of the laptop is that it is small in size (can be put inside a briefcase), can be carried anywhere, has a battery backup and has all the functionality of the desk-top. Laptops can be placed on the lap while working (hence the name). Laptops are costlier than the desktop machines.
Netbook These are smaller notebooks optimized for low weight and low cost, and are designed for accessing web-based applications. Starting with the earliest netbook in late 2007, they have gained significant popularity now. Netbooks deliver the performance needed to enjoy popular activities like streaming videos or music, emailing, Web surfi ng or instant messaging. The word netbook was created as a blend of Internet and notebook.
Tablet Computer has features of the notebook computer but it can accept input from a stylus or a pen instead of the keyboard or mouse. It is a portable computer. Tablet computer are the new kind of PCs.
Handheld Computer or Personal Digital Assistant (PDA) is a small computer that can be held on the top of the palm. It is small in size. Instead of the keyboard, PDA uses a pen or a stylus for input. PDAs do not have a disk drive. They have a limited memory and are less powerful. PDAs can be connected to the Internet via a wireless connection. Casio and Apple are some of the manufacturers of PDA. Over the last few years, PDAs have merged into mobile phones to create smart phones.
Smart Phones are cellular phones that function both as a phone and as a small PC. They may use a stylus or a pen, or may have a small keyboard. They can be connected to the Internet wirelessly. They are used to access the electronic-mail, download music, play games, etc. Blackberry, Apple, HTC, Nokia and LG are some of the manufacturers of smart phones.

Minicomputers are digital computers, generally used in multi-user systems. They have high processing speed and  high storage capacity than the microcomputers. Minicomputers can  support  4–200 users simultaneously. The users can access the  minicomputer  through their PCs or terminal. They are used for  real-time applications in industries, research centers, etc. PDP 11, IBM (8000 series)  are some of the widely used minicomputers.

Mainframe Computers
Mainframe computers  are multi-user, multi-programming and high performance computers. They operate at a very high speed, have very large storage capacity and can handle the workload of many users. Mainframe computers are large and powerful systems generally used in centralized databases. The user accesses the mainframe computer via a terminal that may be a dumb terminal, an intelligent terminal or a PC. A dumb terminal cannot store data or do processing of its own. It has the input and output device only. An intelligent terminal has the input and output device, can do processing, but, cannot store data of its own. The dumb and the intelligent terminal use the processing power and the storage facility of the mainframe computer. Mainframe computers are used in organizations like banks or companies, where many people require frequent access to the same data. Some examples of mainframes are CDC 6600 and IBM ES000 series.

Supercomputers are the fastest and the most expensive machines. They have high processing speed com-
pared to other computers. The speed of a supercomputer is generally measured in FLOPS (Floating point Operations
Per Second). Some of the faster supercomputers can perform trillions of calculations per second. Supercomputers are built
by interconnecting thousands of processors that can work in parallel. Supercomputers are used for highly calculation-intensive tasks, such as, weather forecasting, climate research (global warming), molecular research, biological research, nuclear research and aircraft design. They are also used in major universities, military agencies and scientific research laboratories. Some examples of supercomputers are IBM Roadrunner, IBM Blue gene and Intel ASCI red. PARAM is a series of supercomputer assembled in India by C-DAC (Center for Development of Advanced Computing), in Pune. PARAM Padma is the latest machine in this series. The peak computing power of PARAM Padma is 1 Tera FLOP (TFLOP).

On the basis of working principle

Digital computers:
Digital computers operates on inputs which are on-off type (being digit 1 and 0) and its outputs is also in form of on-off signals. Digital computers are based on counting operation. Any data to be manipulated by a digital computer must first be converted to a discrete(1, 0) representation. There is a practical limit to the accuracy of the readings of analog devices, usually to the nearest tenth of the unit of measure. Thus if water in a beaker was being heated and its temperature rose from 50 C to 51 C ,someone observing the thermometer might only be able to distinguish the temperature  50.0, 50.1, 50.2... 50.9, 51.0. However, on a digital computer, we could simulate to rise in temperature whatever degree of accuracy we want; so that if we wish, we could let the increment be 0.1, 0.01, 0.001,etc.there digital computers are more accurate than analog computers.
Analog computers:
The analog computer operate by measuring rather than counting. It measure continually, usually of a physical nature data such as lengths, voltages, or currents. It does not produce number but produces its results in the form of graph. It is more efficient in continues calculations. Analog machines are usually special purpose devices, dedicated to a single task.
Hybrid computers:
A hybrid computer is combination of both analog and digital computer i.e. a part of processing is done on analog computer and a part on digital computer. A hybrid computer combines the best characteristics of both analog and digital computer. It can accept input data in both analog and digital form. It is used for simulation application.

Computer name
Based on
On/Off, 1/0
On/Off, 1/0
General purpose PCs
Measure elements
Graphs pictures

ECG machines, etc.
Both 0/1& Measure elements
Both On/Off & Graphs
Counting & Measurements
Controlling & monitoring plants. Petrol pumps, Modem, Simulation etc. 

On the basis of brand
On the basis of brand , the computer can be classified as IBM PC, IBM compatibles and Apple/Macintosh computer.
IBM PC is the largest computer manufacturing company establishing USA. The computer manufactures by IBM PC or branded computer. Personal Computer (PC) is the most important type of micro computer system. The micro computer manufacture by IBM company are called IBM PC. These computers are reliable, durable and have better quality but they are costly.

IBM compatibles:
The computers that have some functional characteristics and principles of IBM computer are called IBM compatibles. In other word, all the computer are manufactured by the another companies rather than IBM company are Known as IBM compatibles. All the software and hardware of IBM compatibles. These are cheaper and Their Parts are easily available in Market. they are also duplicate or assemble computer.

Apple/Macintosh Computer
All the computers manufacture by apple cooperation, a leading computers manufacturing computer of USA are known as apple/macintosh computers. These computer use their own software and hardware. They are totally different than that of IBM computers, In terms of both hardware and software. For e.g software developed for apple computer can't run or IBM computers and vice-versa. Similarly, floppy disk formatting in IBM computer can't be recognized by apple macintosh computer and vice-versa. It is popularly used in desktop publishing (DTP) houses as they provide better quality of graphic output.

Mobile Computing
Mobile computing' is a form of human–computer interaction by which a computer is expected to be transported during normal usage. Mobile computing has three aspects: mobile communication, mobile hardware, and mobile software. The first aspect addresses communication issues in ad-hoc and infrastructure networks as well as communication properties, protocols, data formats and concrete technologies. The second aspect is on the hardware, e.g., mobile devices or device components. The third aspect deals with the characteristics and requirements of mobile applications.


Mobile computing is "taking a computer and all necessary files and software out into the field."
"Mobile computing: being able to use a computing device even when being mobile and therefore changing location. Portability is one aspect of mobile computing."  "Mobile computing is the ability to use computing capability without a pre-defined location and/or connection to a network to publish and/or subscribe to information." 
Mobile Computing is a variety of wireless devices that has the mobility to allow people to connect to the internet, providing wireless transmission to access data and information from where ever location they may be.

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