The evolution of electronic computers over a period of time can be traced effectively by dividing this period into various generations. Each generation is characterized by a major technological development that fundamentally changed the way computers operated. These helped to develop smaller, cheaper, powerful, efficient and reliable devices. Now you could 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 generation of computers used vacuum tubes for circuitry and magnetic drums for memory. They were large in size, occupied a lot of space and produced enormous heat. They were very expensive to operate and consumed large amount of electricity. Sometimes the heat generated caused the computer to malfunction. First generation computers operated only on machine language. Input was based on punched cards and paper tape, and output was displayed on printouts. First generation computers could solve only one problem at a time.
The Universal Automatic Computer (UNIVAC) and the Electronic Numerical Integrator And Calculator (ENIAC) are classic examples of first-generation computing devices.
Second Generation - 1956-1963: Transistors The second generation of computers witnessed the vacuum tubes being replaced by transistors. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, energy-efficient and more reliable than their first-generation counter parts. The transistors also generated considerable heat that sometimes caused the computer to malfunction. But it was a vast improvement over the vacuum tube. Second-generation computers used punched cards for input and printouts for output.
Second-generation computers moved from the use of machine language to 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. The computers 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 left its mark in the third generation of computers. Transistors were made smaller in size and placed on silicon chips, which dramatically increased the speed and efficiency of computers.
In this generation, keyboards and monitors were used instead of punched cards and printouts. The computers were interfaced with an operating system which allowed to solve many problems at a time.
Fourth Generation - 1971-Present : Microprocessors The microprocessor brought forth the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet.
Fifth Generation - Present and Beyond: Artificial Intelligence Fifth generation computing devices, based on artificial intelligence, are still in their developmental stage. Fifth generation computers will come close to bridging the gap between computing and thinking.