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Computer History: Classification of Generations of Computers

Alfred is a long-time teacher and computer enthusiast who works with and troubleshoots a wide range of computing devices.

The generations of computers illustrates the miniaturization of transistors and integrated circuit chips over the years

The generations of computers illustrates the miniaturization of transistors and integrated circuit chips over the years

Generations of computers have seen changes based on evolving technologies. With each new generation, computer circuitry, size, and parts have been miniaturized, the processing and speed doubled, memory got larger, and usability and reliability improved.

Note that the timeline specified for each generation is tentative and not definite. The generations are actually based on evolving chip technology rather than any particular time frame.

The five generations of computers are characterized by the electrical current flowing through the processing mechanisms listed below:

  • The first within vacuum tubes
  • The second within transistors
  • The third within integrated circuits
  • The fourth within microprocessor chips
  • The fifth unveiled smart devices capable of artificial intelligence

First Generation of Computers: 1940s-1950s: (Vacuum Tubes and Plugboards)

First generation computers were actually the first general purpose and true digital computers. They came in time to replace the electromechanical systems which were way too slow for assigned tasks.

One task was the need by the USA Army to have machines capable of computing artillery firing tables fast enough. Existing ones took almost two days. When completed, the new machines computed this table data in seconds. Fortunately or unfortunately, they became available only after the end of World War II in 1946.

Vacuum tubes were used in the 1st computer generation

Vacuum tubes were used in the 1st computer generation

The first generation computers used vacuum tubes for amplification and switching purposes. The tubes were made of sealed glass containers, the size of light bulbs. The sealed glass allowed current to flow wirelessly from the filaments to metal plates. And because there were no moving parts in the system, the flow amplified current to enable the computer to manipulate assigned tasks. Vacuum tubes also started and ended the circuitry by switching on and off when turned on or off.

Besides boasting of thousands of resisters and capacitors, these computers would use anything up to and over 17,000 vacuum tubes, which meant computer installations covered entire rooms!

Input and output was done using punch cards, magnetic drums, typewriters and punch card readers. Initially, technicians manually perforated the cards with holes. This was later done using computers.

Interfacing with first gen systems was done using plugboards and machine language. The technicians wired up electrical circuits by connecting numerous cables to plugboards.

Then they slotted in specified punched cards into them and waited for hours for some form of computation while hoping every one of the thousands of vacuum tubes lasted the distance. Lest they went through the procedure again.

A record machine plugboard for IBM 1401

A record machine plugboard for IBM 1401

These machines were intended for low-level operations and thus programming was done using only binary digits 0s and 1s. The systems could solve only one problem at a time. Assembly language and operating system software were nonexistent.

One of the most outstanding computers in this era was The ENIAC (Electronic Numerical Integrator and Computer), which was designed and built by Engineers John W. Mauchly and J. Presper Eckert of the University of Pennsylvania. Its assembly was done by a team of fifty men.

It was 1000 times faster than the previous electromechanical computers but was a little slow when it came to re-programming.

Among many things, The ENIAC was used to study the feasibility of thermonuclear weaponry, firing of ballistic artillery and engine thermal ignition, and elsewhere, for weather predictions.

The left side of The ENIAC computer

The left side of The ENIAC computer

These systems were enormous in size and occupied entire rooms while using lots of electric power. This made them generate unbearable heat.

A list of popular first generation computers:

  • The ENIAC (1946)
  • EDSAC (1949)
  • EDVAC (1950)
  • UNIVAC I (1951)

The UNIVAC (Universal Automatic Computer), still by Engineers John W. Mauchly and J. Presper Eckert, was the first in the same era to be designed for commercial rather than military use. It manipulated both the alphabet and numbers fairly well and was used by USA Census Bureau to enumerate the general population. It was later used to manipulate payrolls, records, company sales, and even predicted presidential election results in 1952.

Unlike the over 17,000 vacuum tubes in The ENIAC, UNIVAC I used slightly over 5,000 vacuum tubes. It was also half the size of its predecessor and sold over 46 units.

 UNIVAC as exhibited in the Vienna Technical Museum

UNIVAC as exhibited in the Vienna Technical Museum

Characteristics of 1st Generation Computers


  • Used vacuum tubes for circuitry
  • Electron emitting metal in vacuum tubes burned out easily
  • Used magnetic drums for memory
  • Were huge, slow, expensive, and many times undependable
  • Were expensive to operate
  • Were power hungry
  • Generated a lot of heat which would make them malfunction
  • Solved one problem at a time
  • Used input based on punched cards
  • Had their outputs displayed in print outs
  • Used magnetic tapes
  • Used machine language
  • Had limited primary memory
  • Were programming only in machine language

Second Generation of Computers: 1950s-1960s: (Transistors and Batch Filing)

These were computers which used transistors instead of vacuum tubes. They were better than their predecessors in many ways because of apparent small size, speed, and cheaper cost.

Transistors are more or less the building blocks of any microchip out there, and also, more reliable, energy efficient and capable of conducting electricity faster and better.

The transistor was used in the 2nd computer generation

The transistor was used in the 2nd computer generation

Just like vacuum tubes, transistors are switches or electronic gates used to amplify or control current, or switch electric signals on and off. They are called semiconductors because they contain elements which lie between conductors and insulators.

Transistor semiconductors were invented at Bell Laboratories in 1947 by scientists William Shockley, John Bardeen and Walter Brattain, but did not see the day of light until mid-1950s.

Second generation computers saw advancement in data input and output procedures. Initially, these processes were similar to the last models of 1st gen computers. They were tedious because they involved multiple personnel carrying punched cards from room to room.

To speed up the process, the batch system was conjured up and implemented. It involved collecting multiple data jobs into multiple punched cards and feeding them into single magnetic tapes using a fairly smaller and inexpensive system. The IBM-1401 was one such computer. Processing, on the other hand, was done using a more powerful system like the IBM 7094.

When data manipulation was complete, the files were transferred back to a magnetic tape. To do this efficiently, IBM's operating system for IBM-7094 system and Fortran Monitor System were used. These were the harbingers of operating system software to come.

Using a smaller system again, say IBM-1401, the data was printed out to multiple punch cards as output.

IBM 1401 computer with one circuit card access drawer opened, on display at the Computer History Museum.

IBM 1401 computer with one circuit card access drawer opened, on display at the Computer History Museum.

Besides the development of operating systems software, other commercial applications were also hitting the 'shelves'. This was probably due to the overall upgrade from restrictive binary based machine code to languages that wholly supported symbolic and alphanumeric coding. Programmers could now write in assemblers and high-level languages like FORTRAN, COBOL, SNOWBALL, and BASIC in 1964.

Punched card as part of a FORTRAN IV program

Punched card as part of a FORTRAN IV program

Characteristics of 2nd Gen Computers


  • Used transistors
  • Faster and more reliable than first generation systems
  • Were slightly smaller, cheaper, faster
  • Generated heat though a little less
  • Still relied on punch cards and printouts for input/output
  • Allowed assembly and high-level languages
  • Stored data in magnetic media
  • Were still costly
  • Needed air conditioning
  • Introduced assembly language and operating system software
Operator's console for IBM 7094 at the Computer History Museum

Operator's console for IBM 7094 at the Computer History Museum

The early mainframes and supercomputers were just some of the machines which took advantage of transistors. The UNIVAC LARC mainframe from Sperry Rand (1960) and IBM-7030 Stretch supercomputer (1961), and CDC 6600 mainframe (1963) were examples of these systems.

Other examples of 2nd Gen computers:

  • IBM-7000
  • CDC 3000 series
  • UNIVAC 1107
  • IBM-7094
  • Honeywell 400

Third Generation of Computers: 1960-1970s (Integrated Circuits and Multi-Programming)

3rd generation computers used the integrated circuit (IC) microchip instead of transistors. The semiconductor IC packed a huge number of transistors, capacitors, diodes, and rectifiers onto a single germanium or silicon. These were then printed on separate parts of a printed circuit board.

The implementation of these computers was also in line with Moore's Law (1965), which observed that transistor size was shrinking so fast, that double the number would fit into new microchips every two years for 10 years to come.

He readjusted this exponential growth after ten years to every five years in 1975.

Integrated circuit on microchip

Integrated circuit on microchip

The IC sought to solve the cumbersome procedures that went into designing the transistor circuitry. The manual interconnection of capacitors, diodes, and rectifiers in transistors was time-consuming and not completely reliable.

Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Corporation separately discovered the benefits of integrated circuits in 1958 and 1959, respectively. Kilby built his IC onto germanium whereas Noyce built one onto a silicon chip.

The first systems to use the IC was the IBM 360, which was packed with the muscle to handle both commercial and scientific assignments.

Jack Kilby's IC chip

Jack Kilby's IC chip

Besides the reduction in cost, the speed and performance of any one computer increased tremendously after placing multiple transistors on a single chip. Since its invention, the IC speed doubled every two years, shrinking both the size and cost of computers even further.

Almost all electronic devices today use some form of integrated circuits placed on printed circuit boards.

The IC circuitry aside, the interaction with computers improved. Instead of punched cards printouts, keyboards and better input peripherals were used to input data which were displayed for output through visual display units.

Computers now used operating system software to manage computer hardware and resources. This allowed systems to run different applications at a time. This was because of centralized applications that monitored memory distribution.

Computers became accessible to the mass audience because of size and fair costing.

This generation also ushered in the concept of 'computer family' which challenged manufacturers to come up with computer components that were compatible with other systems.

A neat looking IBM 370 mainframe released in 1970

A neat looking IBM 370 mainframe released in 1970

Characteristics of 3rd Gen Computers


  • Used ICs
  • Used parallel processing
  • Were slightly smaller, cheaper, faster
  • Used motherboards
  • Data was input using keyboards
  • Output was visualized on the monitors
  • Used operating systems, thus permitting multitasking
  • Simplified programming languages i.e. BASIC

The next generation of mainframes and supercomputers took advantage of integrated circuits (IC). The Scientific Data Systems Sigma 7 (1966) mainframe, and IBM-360 (1964) and CDC 8600 supercomputers (1969) were examples of these systems.

Other examples of third generation computers:

  • IBM-360
  • Personal Data Processor (PDP)
  • IBM-370
	 IBM 360 Mainframe in the German Museum

IBM 360 Mainframe in the German Museum

Fourth Generation of Computers: 1970s to Present (The Microprocessor, OS, and GUI)

The birth of the microprocessor was at the same time the birth of the microcomputer. It was also in line to fulfill Moore's law which predicted exponential growth in transistor and microchips starting in 1965. This generation is instrumental in ushering in diverse devices. The 2nd generation computers which began in 1971 are those in use today.

Intel, through its engineers Ted Hoff, Federico Faggin and Stan Mazor In November 1971, introduced the world's first single chip microprocessor, the Intel 4004. It boasted of 2300 transistors and measured 1/8" by 1/16".

What in the first generation filled an entire room could now fitted in the palm of the hand.

On its own, new microchip was as powerful as The ENIAC computer from 1946. It also merged most of the functions that charged a computer like central processing unit, memory, input and output controls.

The Intel C4004 microprocessor initiated the 4th computer generation

The Intel C4004 microprocessor initiated the 4th computer generation

Manufacturers soon started integrating these microchips in their new computers.

In 1973, the Xerox Alto computer from PARC was released silently. It was a true personal computer and featured an Ethernet port, a mouse, and a bit-mapped graphical user interface, the first of its kind.

The last feature was motivation to Apple computers to build one of a kind. Xerox Alto was powered by a 16bit TI SN74S181N ALU chip from Texas Instruments.

Xerox Alto, arguably the firsst PC from 1973. It was powered by TI SN74S181N ALU chip from Texas Instruments

Xerox Alto, arguably the firsst PC from 1973. It was powered by TI SN74S181N ALU chip from Texas Instruments

Challenged by the Xerox Alto, serious staff began in 1974 when Intel came up with a general purpose 8-bit microprocessor it named 8808. It sought for, and asked Gary Kildall, a consultant, to write an operating system for its new baby. This led to the disk-based operating system software known as Control Program for Microcomputers (CPM).

In 1981, International Business Machine introduced its first computer for the home which ran the 4004 processor. It was known as IBM PC, with PC standing for personal computer. They partnered with Bill Gates who bought Disk Operating System from Seattle Computer Product and had it distributed with IBM's new computer.

The original IBM PC in 1981

The original IBM PC in 1981

The IBM PC architecture became the de facto market standard model, which other PC makers emulated.

Apple under Steve jobs, changed the software game when it released the Apple Macintosh computer with an improved GUI (Graphical User Interface) in 1984, using the interface idea learned from Xerox PARC.

Remember that both Control Program for Microcomputer and Disk Operating System were command-line based operating systems which the user to interface with the computer using the keyboard.

The Apple Macintosh of 1984

The Apple Macintosh of 1984

Following the success of Apple's GUI, Microsoft too integrated a shell version of Windows in the DOS version of 1985. Windows was used like this for the next 10 years until it was reinvented as Windows 95. This was a true operating system software complete with all the right utilities.

Ubuntu running MS Windows 3.11 under VBox

Ubuntu running MS Windows 3.11 under VBox

While software became commonplace and corporations began charging money for it, a new movement of programmers started Linux in 1991. Led by Linux Torvalds, they pioneered a free open source operating system project called Linux.

Besides Linux, other open source operating systems and free software were distributed to cater for office, networking and home computers.

Examples of open source and free software:

  • Ubuntu OS
  • Mozilla Firefox browser
  • Open Office
  • MySQL
  • VLC media player

Through the 1980s and 2000s, personal computers, and desktops, in particular, became commonplace. They were cheap and installed in offices, schools and homes. Software that ran on these computers also became readily available for small money or for free.

Examples of popular personal computer categories:

  • Desktops
  • All-in-one
  • Laptops
  • Workstations
  • Nettops
  • Tablets
  • Smartphones
A desktop computer

A desktop computer

Soon, microprocessors moved out of the reserve of desktop computers into other platforms in businesses and homes. First was the laptop, followed by tablets and smartphones, consoles, embedded systems, and smart cards. These devices increased the need to use the internet while on the move.

The proliferation of mobile computing device soon fought off the dominance of desktops. According to ComScore in the publication Mobile’s Hierarchy of Needs of March 2017, mobiles accounted for 60% of all digital minutes across the world.

A kid using an iPad tablet

A kid using an iPad tablet

Characteristics of 4th Gen Computers


  • Used CPUs which contained thousands of transistors
  • Were much smaller and fitted on a desktops, laps and palms
  • Used a mouse
  • Were used in networks
  • Were cheap
  • Had GUI
  • Were very fast
  • Register over 19 billion transistors in high-end microprocessors (Compare with 2,300 in Intel 4004)

The fourth generation of mainframes and supercomputers evolved to powerful systems:

  • IBM z9 (2005), z10 (2008) and z13 (2015) are examples of mainframes.
  • Cray 1 (1975), Fugitsu K (2011), Titan (2013), Sunway TaihuLight (2016) are examples of supercomputers.
The Cray-1 supercomputer of 1975

The Cray-1 supercomputer of 1975

Fifth Generation of Computers: The Present and The Future

Fifth generation computing is built on technological advancement gained in the previous computer generations. It is meant to headline the 4th Industrial Revolution (4IR).

The implementation is designed to improve human and machine interaction by harnessing human intelligence and taking advantage of the large data that has accumulated since the dawn of the digital age.

It is viewed as the cyber-physical system and arises from the theory, concept and implementation of artificial intelligence (AI) and machine learning (ML). AI and ML may not be the same but are used interchangeably to mean the science of crafting devices and programs which are intelligent enough to interact with humans, other computers, the environment, and programs, by mining big data to achieve set goals.

The proliferation of computing devices with the possibility they can self-learn, respond and interact in normal and probably different ways, based on acquired experience and environment, has also given momentum to the Internet of Things (IoT) concept.

At their peak and with the right algorithms, computers will probably exhibit and process high levels of deep learning, which humans can learn from too.

Many AI projects are already being implemented while others are still in developmental stages. Pioneers in accelerating AI include Google, Amazon, Microsoft, Apple, Facebook, and Tesla.

The initial implementations are now seen on smart home devices which are meant to automate and integrate activities in the house though audio/visual devices, and self-drive cars which are already gracing the roads.

Coral (red) version of the Google Home Mini smart speaker

Coral (red) version of the Google Home Mini smart speaker

The larger goals in AI is to indulge devices to:

  • Understand natural language
  • Recognize human speech
  • See the world in three-dimensional perspective
  • Play interactive games
  • Implement expert input in medical and other complex fields
  • Exercise heuristic classification analysis
  • Implement neural networks

Other areas which are geared towards making AI possible are developments in:

  • Quantum computing
  • Parallel processing

Ongoing AI projects:

  • Virtual personal assistants e.g. Siri, Google Now and Braina.
  • Smart cars e.g. Tesla's autopilot cars and Google's self-driving cars.
  • News generation tools like Wordsmith are used by Yahoo and Fox to generate news snippets.
  • Computer Aided Diagnosis for detection of cancer.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2017 Alfred Amuno


Ana on April 25, 2020:

very informative

Bwambale Benard on April 09, 2020:

Saved me alot!

Batool on April 09, 2020:

Thank you helps me a lot

Oluwabunmi on February 28, 2020:

Please I need the clock speed for the generation of computers

bigoba rafael on February 12, 2020:

thank alot

Shsf on January 18, 2020:

A young

erasto on December 01, 2019:

u deserve to be a profesor

erasto on December 01, 2019:

very helpful bro keep it your deselve to be granted as professor

Praise on November 20, 2019:

Wow AMAZING information

Jackson on November 20, 2019:

Much helpfull keep up bro

Jonas estomih on November 10, 2019:

Very good resourcefull information

Alfred Amuno (author) from Kampala on October 27, 2019:

Thank you Ikram

ikram on October 23, 2019:

this was indeed very helpful

Alfred Amuno (author) from Kampala on October 23, 2019:

Let's wait and observe Fiona.

Fiona on October 15, 2019:

I'm worried that intelligent computers may take over the world today

Frankline Mochama on October 14, 2019:

I wish to get the accurate information (the figures) about physical sizes, heat generated, storage capability, processing speed and capability


Md dilshad on October 09, 2019:

Thanks you for helping

Emile on October 08, 2019:

I wants 6th, 7th,8th,9th,and 10th generation of computer

P-d-Star on October 08, 2019:

Please what year did computer get to 7th generation?

Nouman Ahmed on October 06, 2019:

i want software,Hardware and charecteristics of 6th,7th and also 8th Genration of computers..

Ayuk otang tabong on September 26, 2019:

This was very useful thanks but t[ long to read next time please summarise

Aaron on September 23, 2019:

Thank s for the knowledge

Shek M.Selma on August 26, 2019:

Very good resourceful stuff. Thanks for the detailed information embedded into it. I really like it.

Muhammad on August 18, 2019:


Edmund Mensah on August 08, 2019:

Very good stuff, concise and precise.

juice world official on July 26, 2019:

cool nice like a good lucid dream and everyone check out my new song bye

leadermo on July 10, 2019:

thank you 4help

Michael on July 03, 2019:

Very Helpful. thanks

wali on June 20, 2019:

very helpful very interesting post.

Arrohi on June 10, 2019:

Thanks too much

FAARAAN cRuzer BOy on May 21, 2019:

Thanks very much

yusuf mohammed on April 25, 2019:

well interested but in which year did the fifth generation invented thank,s

abdi on April 15, 2019:


hasini on April 15, 2019:

Thanks a lot

Sven Schubert on April 14, 2019:

the inaccuracies in this article are mind boggling.

Keziah on April 08, 2019:

What is the distinguishing technologies in terms of memory, processor and programming.

MINAHIL on April 05, 2019:

Thanks for the helped a lot of.

Bob on March 19, 2019:

I didn't see any mention of the PHILCO computer S-2000 or the later model S-212. They were available late 50-s and early 60-s. They had the first 48 bit word, which made them very competitive to the IBM systems.

Fakhira muzaffar najar on February 25, 2019:

Name generations of monitors?

someone that needs to know on February 12, 2019:

Which is the most important computing generation??

Iiiii on January 28, 2019:

How fast was the fourth generation computer in MPH or RPM? What was the measurement of the fourth generation computer? Plz respond. Thx

cindy misoi on January 21, 2019:

thanks for the info. It helped a lot

Ebedialu Promise on January 16, 2019:

This nice.

You Good.

Better life ahead of you.

God bless and keep you.


Beki blessed on December 25, 2018:


Sudarshan on November 29, 2018:


Ayesha on November 21, 2018:

Which organization use computer firstly and why?

vipul on November 11, 2018:

thanks for this information

Jade on November 05, 2018:

Thank you! Very useful information. :)

david on September 26, 2018:

nyc one i gained a lot

Omudeke on September 07, 2018:

Thank For That Wonderful Observation.

But I Still Want To Know More On Computer Classifications.

Alfred Amuno (author) from Kampala on September 04, 2018:

Thank you Rorit. You can get some answers in this article:

Rohit on September 04, 2018:

I want( operating system-basic concept)notes for preparation of my first term exams

dhillon on August 08, 2018: