Generation in a computer is a step in technology.It provides a framework for the growth of the computer industry.Originally, the term "generation" was used to distinguish between varying hardware technologies.However,nowadays it has been extended to include both hardware and software,which together make up an entire computer system.

The custom of referring to the computer era in terms of generations into wide use only after 1964.There are totally five computer generations known until today.Each generation has been discussed below in detail along with its identifying characteristics.Although there is a certain amount of overlapping between generations the approximate dates shown against each normally accepted.



During the description of the various computer generations,you will come across several terminologies and computer jargon's,which you might not be aware of,and may not be able to understand properly.However,the idea here is to just give you an overview and technologies will be described an detail in subsequent chapters.Moreover,remember that the objective of this book is also the same-to introduce you to the various concepts about computers.Hence,you will have a better understanding of the terminologies introduced in this section only after you have completed reading this entire book.The objective of this section is mainly to provide an overview of what all you are going to learn in this entire book.

First Generation of Computer (1942-1955):

We have already discussed about some of the early computer-ENIAC,EDVAC,EDSAC,UNIVAC 1 and IBM 701.These machines and others of their time were built by using thousands of vacuum tubes.A vacuum tube was a fragile glass device,which used filaments as a source of electronics and could control and amplify electronic signals.It was the only high-speed electronic switching device available in those days.These vacuum tube computers could perform computations in milliseconds and were referred to as first generation computers.







The memory of these computers was constructed using electromagnetic,relays and all data and instructions were fed into the system from punched cards.The instructions were written in machine and assembly languages because high-level programming languages were introduced much later.Because machine and assembly languages are very difficult to work with,only a few specialists understood how to program these early computers.

The characteristic features of first-generation computer are as follows:

1-They were fastest calculating devices of their time.

2-They were too bulky in size,requiring large rooms for installation.

3-Thousands of vacuum tubes,which were used emitted large amount of head and burnt out frequently.Hence,the room/areas in which these computers were located had to be properly air-conditioned.

4-Each vacuum tube consumed about half a watt of power.Since a computer typically used more than ten thousand vacuum tubes,the power of these computers was very high.

5-As vacuum tubes used filaments,they had a limited life.Since thousands of vacuum tubes were used in making one computer,these computers were prone to frequent hardware failures.

6-Due to low mean time between failures,these computers required almost constant maintenance.

7-In these computers,thousands of individual components had to be assembled manually by hand into functioning circuits.Hence,commercial production of these computers was difficult and costly.

8-Since these computers were difficult to program and use they had limited commercial use.





Second Generation of Computer (1955-1964):



1-A new electronic switching device called transistor was invented at Bell Laboratories in 1947 by John Bardeen,William Shockley and Walter Brattain.Transistors proved to be a better electronic switching device than the vacuum tubes due to their following properties:



1-They were more rugged and easier to handle than tubes since they were made of germanium semiconductor material rather than a glass.

2-They were highly reliable as compared to tubes since they had no part like filament,which could burn out.

3-They could switch much faster (almost ten times faster) tubes.Hence,switching circuits made of transistors could operate much faster than the computer parts made of tubes.

4-They consumed almost one-tenth the power consumed by a tube.

5-They were much smaller than a tube.

6-They were less expensive to produce.

7-They dissipated much less heat as compared to vacuum tubes.

The second-generation computer were manufactured using transistors,instead of vacuum tubes.Due to the properties of transistors listed above the second generation computers were more powerful,more reliable, less expensive,smaller and cooler to operate than the first-generation computers.



The memory of the second-generation computers was composed of magnetic cores.Magnetic disk and magnetic tape were the main secondary storage media used in second-generation computers.Punched cards were still popular and widely used for preparing programs and data to be fed to these computers.



On the software font,the second generation saw the emergence of high-level programming languages and batch operating systems.High-level programming languages like FORTAN,COBOL,ALGOL and SNOBOL were developed during the second generation period which were much easier for people to understand and work with than assembly or machine languages.Hence the second generation computers were easier to program and use than first generation computers.The introduction of batch operating system allowed multiple jobs to be batched together and submitted at a time and automatic transition from one job to another,as soon as the former job finished.This concept in reducing human intervention while processing multiple jobs,resulting in faster processing enhanced throughout and easier operation of second generation computers.



The first generation computers were mainly used for scientific computations.However,in the second generation in increasing usage of computers was seen in business and industry for commercial data processing applications like payroll,inventory control,marketing and production planning.



The characteristic features of second generation computers are as follows:

1-They were more than ten times faster than the first generation computers.

2-They were much smaller than first generation computers requiring small space.

3-Although the heat dissipation was much less than first generation computers,the rooms/areas in which the second generation computers were had to be properly air-conditioned.

4-They consumed much less power than the first generation computers.

5-They were more reliable and less prone to hardware failures than the first generation computers.

6-They had faster and larger primary and secondary storage as compared to first generation computers.

7-They were much easier to program and use than the first generation computers.Hence,they had wider commercial use.

8-In these computers,thousands of individual transistors had to be assembled manually by hand into functioning circuits.Hence,commercial production of these computers was difficult and costly.

Third Generation of Computer:

In 1958,Jack St.Clair Kilby and Robert Noyce invented the first integrated circuit. Integrated circuits (called IC's) are circuits consisting of several electronic components like transistors,resistors and capacitors grown on a single chip of silicon eliminating wired interconnection between components.The IC technology was also known as "microelectronics" technology because it possible integrate larger number of circuit components into very small (less than 5mm square) surface of silicon,known as "chip".Initially the integrated circuits contained only about ten to twenty components.This technology was named small scale integration (SSI).Later,with the advancement in technology for manufacturing IC's,it became possible to integrate up to about hundred components on a single chip.This technology came to be known as medium scale integration (MSI).The third generation was characterised by computers built using integrated circuits.The earlier ones used SSI technology and the later ones used MSI technology. IC's were much smaller,less expensive to produce,more rugged and reliable,faster in operation,dissipated less heat and consumed much less power than circuits built by wiring electronic components manually.Hence,third generation computers were more powerful,more reliable,less expensive,smaller and cooler to operate than the second-generation computers.



Parallel advancements in storage technologies allowed to construction of large magnetic cores based random access memory,and large capacity magnetic disks and magnetic tapes.Hence,the third generation computers typically had few megabytes (less than 5 megabytes) of main memory and magnetic disks capable of storing few tens of megabytes of data per disk drive.



On the software front,the third generation saw the emergence of standardisation of high-level programming languages,time sharing operating systems unbending of software from hardware and the creations of an independent software industry FORTAN COBOL,which were the most popular high-level programming languages in these days,were standardised by the American National Standars Institure (ANSI) in 1966 and 1968 respectively.They were referred to as ANSI,FORTAN and ANSI COBOL.The idea was that as long as computer with an ANSI,FORTAN or ANSI COBOL compiler.Additionally,some more high-level programming languages were introduced during the third-generation period.Notable among these PLAI,PASCAL and Basic.



We saw that in second-generation computer batch operating system was used.In these systems,users had to prepare their data and programs ad then submit them to the computer centre for processing.The operator at the computer centre collected these user jobs and fed them to the computer in batches at scheduled intervals.The output produced for each job was then sent to the computer centre counter for bring returned to some users especially programmers,because often they had to wait for days to locate and correct a few program errors.To remedy this situation,John Kemeny and Thomas Kurtz of Dartmouth College introduced the concept of time sharing operating system.



Time sharing operating system simultaneously allows a large number of users to directly access and share the computing resources in a manner that each user gets the illusion that no one else is using the computer.This is accomplished by having a large number of independent,relatively low-speed terminals simultaneously connected to the main computer.The introduction of time sharing concept helped in drastically improving productivity of programmers and made on-line system feasible,resulting in new on-line application like airline reservation systems,interactive query systems etc.



Until 1965,computer manufactures sold their hardware along with all associated software,and did not charge separately for the software they provided to customers.For example buyer's received language translators for all the language,which could run on the computers they purchased.From the user's standpoint,all this software was free.However,the situation changed in 1969,when IBM and other computer manufactures began to price their hardware and software products separately.This unbundling of software from hardware gave users as opportunity to invest only in software of their need and value.For example,now buyer's could purchase only the language translators they need and not all the language translators on the computer they purchased.This led to the creation of many new software houses,and the beginning of an independent software industry.

The development and introduction of minicomputers,also took place during he third-generation period.The computers built until the early 1960's were mainframe

systems,which only very large companies could afford to purchase and use.



Clearly,a need existed for low-cost smaller computers to fill the gaps left by the bigger,faster and costlier mainframe systems.Several innovators recognised this need and framed new firms in 1960's to produce smaller computers.The first commercially available minicomputer,the PDP-8 (Programmed Data Processor) was introduced in 1965 by Digital Equipment Corporation (DEC).It could easily fit in the corner of a room and did not require the attention of a full-time computer operator.It was based on time sharing operating system and could be accessed simultaneously by a number of users from different locations in the same building.It cost was about one-fourth of the cost of a traditional mainframe system,making it possible for smaller companies to afford computers.It confirmed the tremendous demand for small computers for business and scientific applications and by 1971,there were more than 25 computer manufactures who had entered the minicomputer market.



The characteristic features of third-generation computer are as follows:

1-They were much more powerful than the second-generation computers.They were capable of performing about 1 million instructions per second.

2-They were much smaller than second-generation computer requiring smaller space.

3-Although the heat dissipation was much less than second-generation computers,the rooms/areas in which the third-generation computers were located had to be properly air-conditioned.

4-They consumed much less power than the second-generation computers.

5-They were more reliable and less prone to hardware failures than the second-generation computers.Hence,the maintenance cost was much low.

6-They had faster and larger primary and secondary storage as compared to second-generation computers.

7-They were totally general-purpose machines suitable for both scientific and commercial applications.

8-Their manufacturing did not require manual assembly of individual components and electronic circuits resulting in reduced labor and cost involved at assembly stage.Hence,commercial production of these systems was easier and cheaper.However,highly sophisticated technology and expensive setup was required for the manufacture of IC Chips.

9-Standardisation of high-level programming languages usage and simultaneous use of these systems by a large number of users.

10-Time sharing operating system allowed interactive usage and simultaneous use of these systems by a large number of users.

11-Time sharing operating system helped in drastically improving the productivity of programmers,cutting down the time and cost of program development by several fold.

12-Time sharing operating system also made on-line systems feasible,resulting in the usage of these systems for new on-line applications.

13-Unbundling of software from hardware gave users of these systems an opportunity to invest only in software of their need and value.

14-The minicomputers of the third-generation made computers affordable even by smaller companies.

Fourth Generation of Computer(1975-1989):

The average number of electronic components packed on a silicon chip doubled each year after 1965.This progress soon led to era of large scale integration (LSI) when it was possible to integrate over 30,000 electronic components on a single chip,followed by very large integration (VLSI) when it was possible to integrate about one million electronic components on a single chip.This progress led to perform dramatic development - the creation of a microprocessor.A microprocessor contains all the circuits needed to perform arithmetic logic and control functions.the core activities of all computers,on a single chip.



Hence,it became possible to build a complete computer with a microprocessor,a few additional primary storage chips and other support circuitry.It started a new social revolution-the personal computer (PC)revolution.Overnight,computers became incredibly compact.They became inexpensive to make, and suddenly it became possible for anyone to own a computer.



During the fourth generation magnetic core memories were replaced by semiconductor memories,resulting in large random access memories with very fast access time.On the other hand,hard disks became cheaper,smaller and larger in capacity.Parallely,in addition to magnetic tapes,floppy disks became popular as a portable medium for porting programs and data from one computer system to another.



Another significant development during the fourth generation period was the spread of high-speed computer networking,which enabled multiple computers to be connected together to enable them to communicate and share data.Local areas networks (LANs) became popular for connecting several dozen or even several hundred computers within an organization or within an campus and wide area networks (WAN's) became popular for connecting computers located at larger distances.This gave rise to network of computers and distributed systems.



Ont the software front,there were several new developments which engaged which emerged to match the new technologies of the fourth generation.For example,several new operating systems were developed for PCs.Notable among these were MS-DS,MS Windows and Apple's propriety OS.Because the PCs were to be used by individuals who were not computer professionals to make computers more user friendly (easier to use) companies developed graphical user interface.A graphical user interface (GUI) Provides icons (pictures) and menus (list of choices)which based applications were more developed to make PCs a powerful tool.Notable among these were powerful word processing packages,which allowed easy development of documents,spreadsheet package which allowed easy manipulation and analysis of data organised in columns and rows and graphic packages.which allowed easy drawing of pictures and diagrams.Another very useful concept,which became popular during the fourth generation period was that of multiple windows on a single terminal screen.



This feature allowed users to simultaneously see the current status of several applications in separate windows on the same terminal screen.During the fourth generation period the UNIX operating system and the C programming language also became very popular

The characteristic features of the fourth-generation computer are as follows:



1-The PCs were smaller and cheaper than mainframes and minicomputers of the third generation.

2-The mainframes were much powerful than the third-generation systems.

3-Although the mainframes required proper air-conditioning of the room ares in which they were located,no air-conditioned was required for PCs.

4-They consumed much less power than third-generation computers.

5-They were more feature and less prone to hardware failures than the third-generation computers.Hence,the maintenance cost was negligible.

6-They had faster and larger primary and secondary storage as compared to third-generation computers.

7-They were totally general purpose machines.

8-Their manufacturing did not require manually of individual components into electronic circuits,resulting in reduced human labour and cost involved at Assembly stage.Hence,commercial production of these systems was easier and cheaper.However,highly sophisticated technology and expensive setup was required for the manufacture of LSI and VLSI chips.

9-Use of standart high-level programming languages allowed programs written for one computer to be easily ported to and executed on another computer.

10-Graphical User Interface (GUI) enabled new users to quickly learn how to use computers.

11-PC based applications made the PCs powerful tool for both office and home page.

12-Network of computers enabled sharing of resources like disks,printers etc among multiple computers and their users.They also enabled several new types o applications involving interaction among computers users of geographically distant locations.Computer Supported Cooperate Working (CSCW) or groupware is one such application,in which multiple members working on a single project and located at distant locations.Cooperate with each other by using a network of computers.

13-In addition to unbundled software,these systems also used add-on hardware feature,which allowed users o invest only in the hardware configuration and software of their need and value.

14-The PCs of the fourth-generation made computers affordable even by individuals for their personal use at home.

Fifth Generation of Computer(1989-Present):