The 4 Generations of Computers

By Anisha Ahmed

The Generation:

Computing hardware evolved from machines that needed separate manual action to perform each arithmetic operation, to punched card machines, and then to stored-program computers. The history of stored-program computers relates first to computer architecture, that is, the organization of the units to perform input and output, to store data and to operate as an integrated mechanism.


Before the development of the general-purpose computer, most calculations were done by humans. Mechanical tools to help humans with digital calculations were then called "calculating machines", by proprietary names, or even as they are now, calculators. It was those humans who used the machines who were then called computers. Aside from written numerals, the first aids to computation were purely mechanical devices which required the operator to set up the initial values of an elementary arithmetic operation, then manipulate the device to obtain the result. A sophisticated (and comparatively recent) example is the slide rule, in which numbers are represented as lengths on a logarithmic scale and computation is performed by setting a cursor and aligning sliding scales, thus adding those lengths. Numbers could be represented in a continuous "analog" form, for instance a voltage or some other physical property was set to be proportional to the number. Analog computers, like those designed and built by Vannevar Bush before World War II were of this type. Numbers could be represented in the form of digits, automatically manipulated by a mechanical mechanism. Although this last approach required more complex mechanisms in many cases, it made for greater precision of results.


Colossus: The World's First Electronic Computer - The Four Generations of Computers (1/4)
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The first Generation (1945 - 1955)

Very large computers made up of vacuum tubes and often programmed using wiring plugboards

- Programmed using machine language

- Mostly used for numerical calculations as working out mathematical tables

- No OS


The Second Generation (1955 - 1965)

- Mainframes made up of transistors

- Mainframes made up of transistors

- At first punch cards were used to provide input, then tapes were used (for batch processing)

- Used Assemblers and FORTRAN compilers for program writing

-Simple batch processing was used with input files, programs and output on tape

- Smaller computers (e.g. IBM 1401) was used to read programs and data on punch cards on to input tapes and for offline printing

- Used mainly for scientific and engineering applications

- FMS (Fortran Monitor System) and IBM IBSEN as OS's for handling jobs (e.g. to read a job and to run it).


The Third Generation (1965 - 1980)

-Mainframes based on small scale ICs were used.

- Capable of multiprogramming (running several jobs at the same time)

- Fixed disks were used and new jobs on cards to be executed could be read on to the disk while executing other jobs (spooling)

- Though the first models used multiprogrammed batch processing, to cater to increased response time, timesharing was introduced later (Time-sharing Systems)

- Complex OSs as OS/360 were used.

- Used for various applications including scientific and business applications

- Mini computers also appeared on the market which were used by small departments etc. and became the platform for UNIX.


The Fourth Generation (1980 . . . )

- Mainframes, Minicomputers, Workstations, Personal Computers (Desktop and portable) based on VLSI components

- Network operating systems that facilitate file sharing, remote logging etc. and Client Server computing.

- Distributed OSs that make use of multiple machines and processors to run applications.

- GUI based OS interfaces and applications.

- Virtual Machines and Network Computers (NCs).