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History of Computers | Types | Generations

History of Computers | Types | Generations

The term computer is derived from the word compute. The word compute means to calculate. A computer is an electronic machine that accepts data from the user, processes the data by performing calculations and operations on it, and generates the desired output results. The computer performs both simple and complex operations, with speed and accuracy. 


A digital computer uses distinct values to represent the data internally. All information is represented using the digits 0s and 1s. The computers that we use at our homes and offices are digital.

An Analog computer is another kind of computer that represents data as a variable across a continuous range of values. The earliest computers were analog computers. Analog computers are used for measuring parameters that vary continuously in real-time, such as temperature, pressure, and voltage. Analog computers may be more flexible but generally less precise than digital computers. The slide rule is an example of an analog computer.


Speed, accuracy, diligence, storage capability, and versatility are some of the key characteristics of a computer. A brief overview of these characteristics is


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.


A computer provides a high degree of accuracy. For example, the computer can accurately give the result of the division of any two numbers up to 10 decimal places.


When used for a longer period, 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 floppy disks and compact disks can store a large amount of data permanently.


A 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 at the next moment, you may play music or print a document.

Computers have several limitations too. A computer can only perform tasks that it has been programmed to do. The computer cannot do any work without instructions from the user. It executes instructions as specified by the user and does not take its own decisions.


Until the development of the first generation computers based on vacuum tubes, there had been several developments in computing technology related to mechanical computing devices. The key developments that took place till the first computer was developed are as follows,

  • Calculating Machines ABACUS was the first mechanical calculating device for counting large numbers. The word ABACUS means calculating board. It consists of bars in horizontal positions on which sets of beads are inserted. The horizontal bars have 10 beads each, representing units, tens, hundreds, etc. 
  • Napier’s bones was a mechanical device built for the purpose of multiplication in 1617 AD. by an English mathematician John Napier.
  • Slide Rule was developed by an English mathematician Edmund Gunther in the 16th century. Using the slide rule, one could perform operations like addition, subtraction, multiplication, and division. It was used extensively till the late 1970s. 
  • Pascal’s Adding and Subtraction Machine was developed by Blaise Pascal. It could add and subtract. The machine consisted of wheels, gears, and cylinders.
  • Leibniz’s Multiplication and Dividing Machine was a mechanical device that could both multiply and divide. The German philosopher and mathematician Gottfried Leibniz built it around 1673.
  • Punch Card System was developed by Jacquard to control the power loom in 1801. He invented the punched card reader that could recognize the presence of a hole in the punched card as binary one and the absence of the hole as binary zero. The 0s and 1s are the basis of the modern digital computer.
  • Babbage’s Analytical Engine an English man Charles Babbage built a mechanical machine to do complex mathematical calculations, in the year 1823. The machine was called a Difference Engine. Later, Charles Babbage and Lady Ada Lovelace developed a general-purpose calculating machine, the analytical engine. 

Charles Babbage is also called the father of computers.

  • Hollerith’s Punched Card Tabulating Machine was invented by Herman Hollerith. The machine could read the information from a punched card and process it electronically.

All of the above-mentioned machines resulted in the development of the first computer in the 1940s.


The computer has evolved from a large-sized simple calculating machine to a smaller but much more powerful machine. The evolution of computers to the current state is defined in terms of the generations of computers. Each generation of computers is designed based on new technological development, resulting in better, cheaper, and smaller computers that are more powerful, faster, and more efficient than their predecessors. Currently, there are five generations of computers. In the following subsections, we will discuss the generations of computers in terms of

  • Technology (hardware and software),
  • Computing Characteristics (speed, i.e., number of instructions executed per second),
  • Physical Appearance
  • Applications

First Generation (1940 to 1956): Using Vacuum Tubes

Hardware Technology: The first generation of computers used vacuum tubes for circuitry and magnetic drums for memory. The input to the computer was through punched cards and paper tapes. The output was displayed as printouts.

Software Technology: The instructions were written in machine language. Machine language uses 0s and 1s for coding the instructions. The first generation computers could solve one problem at a time.

Computing Characteristics: The computation time was in milliseconds.

Physical Appearance: These computers were enormous in size and required a large room for installation.

Application: They were used for scientific applications as they were the fastest computing device of their time.


  • Universal Automatic Computer (UNIVAC)
  • Electronic Numerical Integrator And Calculator (ENIAC)
  • Electronic Discrete Variable Automatic Computer (EDVAC)

The first generation computers used a large number of vacuum tubes and thus generated a lot of heat. They consumed a great deal of electricity and were expensive to operate. The machines were prone to frequent malfunctioning and required constant maintenance. Since first-generation computers used machine language, they were difficult to program.

Second Generation (1956 to 1963): Using Transistors

Hardware Technology: Transistors replaced the vacuum tubes of the first generation of computers. Transistors allowed computers to become smaller, faster, cheaper, energy-efficient, and reliable. The second-generation computers used magnetic core technology for primary memory. They used magnetic tapes and magnetic disks for secondary storage. The input was still through punched cards and the output using printouts. They used the concept of a stored program, where instructions were stored in the memory of the computer.

Software Technology: The instructions were written using the assembly language. Assembly language uses mnemonics like ADD for addition and SUB for subtraction for coding the instructions. It is easier to write instructions in assembly language, as compared to writing instructions in machine language. High-level programming languages, such as early versions of COBOL and FORTRAN were also developed during this period.

Computing Characteristics: The computation time was in microseconds.

Physical Appearance: Transistors are smaller in size compared to vacuum tubes, thus, the size of the computer was also reduced.

Application: The cost of commercial production of these computers was very high, though less than the first generation computers. The transistors had to be assembled manually in second-generation computers.


        • PDP-8
        • IBM 1401
        • CDC 1604

Second-generation computers generated a lot of heat but much less than first-generation computers. They required less maintenance than the first generation computers.

Third Generation (1964 to 1971): Using Integrated Circuits

Hardware Technology: The third generation computers used the Integrated Circuit (IC) chips. In an IC chip, multiple transistors are placed on a silicon chip. Silicon is a type of semiconductor. The use of IC chips increased the speed and the efficiency of the computer, manifold. The keyboard and monitor were used to interact with the third generation computer, instead of the punched card and printouts.

Software Technology: The keyboard and the monitor were interfaced through the operating system. The operating system allowed different applications to run at the same time. High-level languages were used extensively for programming, instead of machine language and assembly language.

Computing Characteristics: The computation time was in nanoseconds.

Physical Appearance: The size of these computers was quite small compared to the second generation computers.

Application: Computers became accessible to mass audiences. Computers were produced commercially and were smaller and cheaper than their predecessors.


  • IBM 370
  • PDP 11

The third generation computers used less power and generated less heat than the second generation computers. The cost of the computer was reduced significantly, like individual components of the computer were not required to be assembled manually. The maintenance cost of the computers was also less compared to their predecessors.

Fourth Generation (1971 to present): Using Microprocessors

Hardware Technology: They use the Large Scale Integration (LSI) and the Very Large Scale Integration (VLSI) technology. Thousands of transistors are integrated on a small silicon chip using LSI technology. VLSI allows hundreds of thousands of components to be integrated into a small chip. This era is marked by the development of microprocessors. The microprocessor is a chip containing millions of transistors and components, and, designed using LSI and VLSI technology.

This generation of computers gave rise to Personal Computer (PC). Semiconductor memory replaced the earlier magnetic core memory, resulting in fast random access to memory. Secondary storage devices like magnetic disks became smaller in physical size and larger in capacity. The linking of computers is another key development of this era.

The computers were linked to form networks that led to the emergence of the Internet. This generation also saw the development of pointing devices like mice and handheld devices.

Software Technology: Several new operating systems like the MS-DOS and MS-Windows developed during this time. This generation of computers supported Graphical User Interface (GUI). GUI is a user-friendly interface that allows users to interact with the computer via menus and icons. High-level programming languages are used for the writing of programs.

Computing Characteristics: The computation time is in picoseconds.

Physical Appearance: They are smaller than the computers of the previous generation. Some can even fit into the palm of the hand.

Application: They became widely available for commercial purposes. Personal computers became available to the home user.


  • The Intel 4004 chip was the first microprocessor. The components of the computer like the Central Processing Unit (CPU) and memory were located on a single chip.
  • In 1981, IBM introduced the first computer for home use. 
  • In 1984, Apple introduced the Macintosh.

The microprocessor has resulted in the fourth generation computers being smaller and cheaper than their predecessors. The fourth-generation computers are also portable and more reliable.

They generate much lesser heat and require less maintenance compared to their predecessors. GUI and pointing devices facilitate easy use and learning on the computer. Networking has resulted in resource sharing and communication among different computers.

Fifth Generation (Present and Next): Using Artificial Intelligence

The goal of fifth-generation computing is to develop computers that are capable of learning and self-organization. The fifth-generation computers use Super Large Scale Integrated (SLSI) chips that can store millions of components on a single chip. These computers have large memory requirements.

This generation of computers uses parallel processing that allows several instructions to be executed in parallel, instead of serial execution. Parallel processing results in faster processing speed. The Intel dual-core microprocessor uses parallel processing.

The fifth-generation computers are based on Artificial Intelligence (AI). They try to simulate the human way of thinking and reasoning. Artificial Intelligence includes areas like Expert System (ES), Natural Language Processing (NLP), speech recognition, voice recognition, robotics, etc.

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