Computer Generations : Classification of Computers on the basis of generations

The evolution of computers can be divided into five generations. The term generation is used to characterized the major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable devices. There are five generations in all, and each, starting with the second, is marked with improvements over the previous ones. 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. The five generations of computer is as follows :


1. First-generation : Vaccum Tubes (1945-55) : The first generation of computers are used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. These computers were very expensive to operate and because they used vaccum tubes, so they needs a great deal of electricity. The first computers generated a lot of heat, which was often the cause of malfunctions. Moreover, these tubes burned out because of too much heating and need to be replaced more frequent. The operation cost of these computers were too expensive.


Figure : Vaccum Tubes

First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. It would take operators days or even weeks to set-up a new problem. Input was based on punched cards and paper tape, and output was displayed on printouts.  There was great difficulty to program these computers ,and more when there were some malfunctions. The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.

The Key Features of First-Generation Computers are as follows :

  • They use vacuum tubes for circuitry and magnetic drum for memory.
  • Programming for this generation was done using machine language i.e. the language of ‘0’s and ‘1’s.
  • They lack in versatility and speed. Computation time was millisecond.
  • They were mostly used for scientific application.
  • They were very expensive and consumed electricity in large amount.
  • They had poor reliability and accuracy.

2. Second Generation : Transistors (1956-1965) : The second-generation computer used transistors for CPU components, ferrite cores for main memory, magnetic disks for secondary memory. 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. 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 1948 by scientists William Shockley, John Bardeen and Walter Brattain. Second-generation computers still relied on punched cards for input and printouts for output.


Figure : Transistors

The Second-generation computers moved from cryptic binary machine language to symbolic, or 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. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology. Some examples of second generation computers include: IBM 1920, IBM 1401, PDP-8 and CDC 1604.

The Key Features of Second-Generation Computers are as follows :
  • Transistors were used as CPU.
  • A single transistor was equivalent to circuit produced by several hundred vacuum tubes. Therefore, the size and cost of computers got reduced considerably.
  • These computers used magnetic core as main memory and used punched card readers for input and printers output.
  • They were more reliable and have less chances of hardware malfunction.
  • Generated low levels of heat. The need for air conditioning was therefore reduced.
  • They were having higher speed than first generation computers. The computation speed was now microsecond.

3. Third Generation : Integrated Circuits (1965-1980) : The development of the integrated circuit was the hallmark of the third generation of computers. Third generation computers used the integrated circuit (IC) microchip instead of transistors. Transistors were miniaturized and placed on silicon chips, called semiconductors. 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, which drastically increased the speed and efficiency of computers.


Figure : Integreted Circuits


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.

One of the most noticeable achievement of third generation computers is the development of operating systems. The operating systems allowed the machines to run many different applications. These applications were monitored and coordinated by the computer’s memory. Now, Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors. Some examples of third generation computers were: IBM-360 series, CDC 1700, and PDP-11.

The Key Features of Third-Generation Computers are as follows :

  • Transistors were replaced by Integrate Circuits.
  • Computers used lesser power and generated lesser heat. Maintenance requirements also reduced considerably.
  • Magnetic core was replaced by micro-chip.
  • Keyboards were used to provide input and monitors were used to get the output from the machine.
  • Operating system and other application software was used.
  • Computers now have become much smaller, faster and more reliable. The speed of computation was now Nano second.
  • The cost has also reduced considerably.

4. Fourth Generation : Microprocessors (19680-Present) : The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The fourth generation of computers uses large scale Integrated Circuits (LSIC) built on a single silicon chip called microprocessors. Due to the development of microprocessor it is possible to place computer’s central processing unit (CPU) on single chip. These computers are called microcomputers. Later very large scale Integrated Circuits (VLSIC) replaced LSICs.


Figure : Microprocessor


The personal computer (PC) that we see in our school and offices are Fourth Generation Computers. In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.

The Key Features of Fourth-Generation Computers are as follows :
  • Integrate Circuits were replaced by Microprocessors.
  • Computers in this era started using Large Scale Integration (LSI), Very Large Scale Integration (VLSI) and Ultra Large Scale Integration (ULSI) technology.
  • Semiconductor memory replaced magnetic memory of previous generation computers.
  • Secondary storage devices became smaller in size and large in capacity.
  • Now computers could be connected using LAN, WAN and MAN.
  • Pointing devices like mouse were introduced.
  • High level languages like C and C++ are used for writing programs.
  • The computation speed has increased to picosecond.
  • The size of computer has been reduced even further.
  • Computers are widely used for commercial as well as personal purpose.

5. Fifth Generation: Artificial Intelligence (Present and Beyond) : The starting point for fifth generation computer has been set in early 1990’s. They are programmed to work according to the artificial intelligence provided to them. Artificial intelligence would make them simulate the human way of thinking and reasoning. Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.

The Key Features of Fifth-Generation Computers are as follows :

  • Working based on artificial intelligence.
  • Voice recognition has also become a mode to provide input to the computers.
  • Concept of robotics surgery could be made possible.
  • Use of Super Large Scale Integrated (SLSI) Circuits incorporating ten million electronic components on a single chip.
  • Speed and size of main memory and secondary memory have doubled and tripled in volume.
  • Use of multimedia applications and internet based applications.
  • Portable computers, more powerful, cheaper, reliable and easier to use desktop machines.




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