Computer Generations

“Generation” in computer talk is a step in technology. It provides a framework for the growth of computer industry. Basically it was used to distinguish between various hardware technologies, but now it has been extended to include both hardware and software. Till now there are five new computer generations. Each of five generations of computer is characterized by a major Technological Developmentthat fundamentally changes the way computers operate.

Result of new generation development:

·    Smaller computer devices

·    Cheaper

·    More powerful and more effective

·    Reliable computing devices

·    Faster

·    Energy efficient

Now let’s start with the first generation of computer.

First Generation Computers: Vacuum Tubes (1940-1956)

Vacuum tube is a device that controls electric current through a vacuum in a sealed container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament. This type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect. Not all electron tubes contain vacuum: gas-filled tubes are devices that rely on the properties of a discharge through an ionized gas. The simplest vacuum tube, the diode, contains only an electron emitting cathode and an electron collecting plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the hot cathode travel through the tube and are collected by the anode. Adding control grids within the tube allows control of the current between the two electrodes. Tubes with grids can be used as electronic amplifiers, rectifiers, electronically controlled switches, oscillators, and for other purposes.

A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure. Most tubes have glass envelopes, though ceramic and metal envelopes (atop insulating bases) have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal. On most tubes, the leads, in the form of pins, plug into a tube socket for easy replacement of the tube (tubes were by far the most common cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves). Some tubes had an electrode terminating at a top cap which reduced interelectrode capacitance to improve high-frequency performance, kept a possibly very high plate voltage away from lower voltages, and could accommodate one more electrode than allowed by the base.

The earliest vacuum tubes evolved from incandescent light bulbs, containing a filament sealed in an evacuated glass envelope. When hot, the filament releases electrons into the vacuum, a process called thermionic emission. A second electrode, the anode or plate, will attract those electrons if it is at a more positive voltage. The result is a net flow of electrons from the filament to plate. However, electrons cannot flow in the reverse direction because the plate is not heated and does not emit electrons. The filament (cathode) has a dual function: it emits electrons when heated; and, together with the plate, it creates an electric field due to the potential difference between them. Such a tube with only two electrodes is termed a diode, and is used for rectification. Since current can only pass in one direction, such a diode (or rectifier) will convert alternating current (AC) to pulsating DC. This can therefore be used in a DC power supply, and is also used as a demodulator of amplitude modulated (AM) radio signals and similar functions.

Early tubes used the directly heated filament as the cathode. Many more modern tubes employ indirect heating, with a separate electrically isolated "heater" inside a tubular cathode. The heater is not an electrode, but simply serves to heat the cathode sufficiently for thermionic emission of electrons. This allowed all the tubes to be heated through a common circuit (which can as well be AC) while allowing each cathode to arrive at a voltage independently of the others, removing an unwelcome constraint on circuit design.

The filaments require constant and often considerable power, even when amplifying signals at the microwatt level. Power is also dissipated when the electrons from the cathode slam into the anode (plate) and heat it; this can occur even in an idle amplifier due to quiescent currents necessary to ensure linearity and low distortion. In a power amplifier, this heating can be considerable and can destroy the tube if driven beyond its safe limits. Since the tube contains a vacuum, the anodes in most small and medium power tubes are cooled by radiation through the glass envelope. In some special high power applications, the anode forms part of the vacuum envelope to conduct heat to an external heat sink, usually cooled by a blower.

Klystrons and magnetrons often operate their anodes (called collectors in klystrons) at ground potential to facilitate cooling, particularly with water, without high voltage insulation. These tubes instead operate with high negative voltages on the filament and cathode.

Except for diodes, additional electrodes are positioned between the cathode and the plate (anode). These electrodes are referred to as grids as they are not solid electrodes but sparse elements through which electrons can pass on their way to the plate. The vacuum tube is then known as a triode, tetrode, pentode, etc., depending on the number of grids. A triode has three electrodes: the anode, cathode, and one grid, and so on. The first grid, known as the control grid, (and sometimes other grids) transforms the diode into a voltage-controlled device: the voltage applied to the control grid affects the current between the cathode and the plate. When held negative with respect to the cathode, the control grid creates an electric field which repels electrons emitted by the cathode, thus reducing or even stopping the current between cathode and anode. As long as the control grid is negative relative to the cathode, essentially no current flows into it, yet a change of several volts on the control grid is sufficient to make a large difference in the plate current, possibly changing the output by hundreds of volts (depending on the circuit). The solid-state device which operates most like the pentode tube is the junction field-effect transistor (JFET), although vacuum tubes typically operate at over a hundred volts, unlike most semiconductors in most applications.

During the period of 1940 to 1956 first generation of computers were developed. The first generation computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. The vacuum tube was developed by Lee DeForest. A vacuum tube is a device generally used to amplify a signal by controlling the movement of electrons in an evacuated space. First generation computers were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions.

Hardware Technologies of First Generation Computers

·      Vacuum tubes

·      Electromagnetic relay memory

·      Punch cards secondary storage

Software Technologies of First Generation Computers

·    Machine and assembly language

·    Stored programme concept

·    Mostly scientific applications

Characteristics

1) First generation computers were based on vacuum tubes.

2) The operating systems of the first generation computers were very slow.

3) They were very large in size.

4) Production of the heat was in large amount in first generation computers.

5) Machine language was used for programming.

6) First generation computers were unreliable.

7) They were difficult to program and use.

8) Do only one work at one time.

9) It had limited commercial use.

Examples

UNIVAC, EDVAC, EDSAC, IBM 701 and ENIAC computers are examples of first generation computing devices.

Second Generation Computers: Transistors (1956-1963)

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. The transistor was invented in 1947 by three scientists J. Bardeen, H.W. Brattain and W. Shockley. A transistor is a small device made up of semiconductor material like germanium and silicon.

The semiconductor material is given special properties by a chemical process called doping. The doping results in a material that either adds extra electrons to the material (which is then called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal structure (which is then called P-type because it results in more positive charge carriers). The transistor's three-layer structure contains an N-type semiconductor layer sandwiched between P-type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN configuration).

A small change in the current or voltage at the inner semiconductor layer (which acts as the control electrode) produces a large, rapid change in the current passing through the entire component. The component can thus act as a switch, opening and closing an electronic gate many times per second. Today's computers use circuitry made with complementary metal oxide semiconductor (CMOS) technology. CMOS uses two complementary transistors per gate (one with N-type material; the other with P-type material). When one transistor is maintaining a logic state, it requires almost no power.

Transistors are the basic elements in integrated circuits (ICs), which consist of very large numbers of transistors interconnected with circuitry and baked into a single silicon microchip or "chip."

A transistor computer is a computer which uses discrete transistors instead of vacuum tubes. The "first generation" of electronic computers used vacuum tubes, which generated large amounts of heat, were bulky, and were unreliable. A "second generation" of computers, through the late 1950s and 1960s featured boards filled with individual transistors and magnetic memory cores.

During the period of 1956 to 1963 second generation of computers were developed. The second generation computers emerged with development of Transistors. Even though the Transistor were developed in 1947 but was not widely used until the end of 50s. The transistor made the second generation computers faster, smaller, cheaper, more energy-efficient and more reliable than their first-generation computers. Even though the transistor used in the computer generated enormous amount of heat which ultimately would lead to the damage of the computers but was far better than vacuum tubes.

Second generation computers used the low level language i.e. machine level language and assembly language which made the programmers easier to specify the instructions. Later on High level language programming were introduced such as COBOL and FORTRAN. Magnetic core was used as primary storage. Second generation computer has faster input /output devices which thus brought improvement in the computer.

Hardware Technologies of Second Generation Computers

·    Transistors

·    Magnetic core memory

·    Magnetic tapes

·    Disks for secondary storage

Software Technologies of Second Generation Computers

·    Batch Operating system

·    High level programming language

·    Scientific and commercial applications

Characteristics

1) Transistors were used in place of vacuum tubes.

2) Second generation computers were smaller in comparison with the first generation computers.

3) They were faster in comparison with the first generation computers.

4) They generated less heat and were less prone to failure.

5) They took comparatively less computational time.

6) Assembly language was used for programming.

7) Second generation computers has faster input/output devices.

Examples

IBM 7000, NCR 304, IBM 650, IBM 1401, ATLAS and Mark III are the examples of second generation computers.

Third Generation Computers: Integrated Circuits (1964-1971)

An electronic circuit formed on a small piece of semiconducting material, which performs the same function as a larger circuit made from discrete components. An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small plate ("chip") of semiconductor material, normally silicon. This can be made much smaller than a discrete circuit made from independent components. ICs can be made very compact, having up to several billion transistors and other electronic components in an area the size of a fingernail. The width of each conducting line in a circuit can be made smaller and smaller as the technology advances; in 2008 it dropped below 100 nanometer and now it is tens of nanometers.

The first integrated circuits contained only a few transistors. Called "small-scale integration" (SSI), digital circuits containing transistors numbering in the tens provided a few logic gates for example, while early linear ICs such as the Plessey SL201 or the Philips TAA320 had as few as two transistors. The term Large Scale Integration was first used by IBM scientist Rolf Landauer when describing the theoretical concept, from there came the terms for SSI, MSI, VLSI, and ULSI.

The next step in the development of integrated circuits, taken in the late 1960s, introduced devices which contained hundreds of transistors on each chip, called "medium-scale integration" (MSI).

An IC is a small wafer, usually made of silicon, that can hold anywhere from hundreds to millions of transistors, resistors, and capacitors. These extremely small electronics can perform calculations and store data using either digital or analog technology.

Digital ICs use logic gates, which work only with values of ones and zeros. A low signal sent to to a component on a digital IC will result in a value of 0, while a high signal creates a value of 1. Digital ICs are the kind you will usually find in computers, networking equipment, and most consumer electronics.

Analog or linear ICs work with continuous values. This means a component on a linear IC can take a value of any kind and output another value. The term "linear" is used since the output value is a linear function of the input. For example, a component on a linear IC may multiple an incoming values by a factor of 2.5 and output the result.

During the period of 1964 to 1971 Third generation computers were developed. The third generation computers emerged with the development of IC (Integrated Circuits). The invention of the IC was the greatest achievement done in the period of third generation of computers. IC was invented by Robert Noyce and Jack Kilby in 1958-59. IC is a single component containing a number of transistors. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers.

Keyboards and monitors developed during the period of third generation of computers. The third generation computers 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. 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. Third generation computers use large magnetic cores as memory which is much better than the previous generation. This generation was much energy efficient than the previous generation and that’s why it produces less heat and less damage to the computer hardware.

Hardware Technologies of Third Generation Computers

·      ICs with SSI and MSI technologies

·      Larger magnetic core memory

·      Large capacity disks magnetic tapes secondary storage

Software Technologies of Third Generation Computers

·    Timesharing operating system

·    Standardization of high level programming language

·    Unbundling of software from hardware

Characteristics

1) IC was used instead of transistors in the third generation computers.

2) Third generation computers were smaller in size and cheaper as compare to the second generation computers.

3) They were fast and more reliable.

4) High level language was developed.

5) Magnetic core and solid states as main storage.

6) They were able to reduce computational time and had low maintenance cost.

7) Input/Output devices became more sophisticated.

8) It was commercially easy to use and upgrade.

9) Scientific, commercial and interactive on-line applications were developed.

Examples

PDP-8, PDP-11, ICL 2900, IBM 360 and IBM 370 are the examples of third generation computers.

Fourth Generation Computers: Microprocessor (1971-present)

A microprocessor incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC), or at most a few integrated circuits. All modern CPUs are microprocessors making the micro- prefix redundant. The microprocessor is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequential digital logic, as it has internal memory. Microprocessors operate on numbers and symbols represented in the binary numeral system.

The integration of a whole CPU onto a single chip or on a few chips greatly reduced the cost of processing power. The integrated circuit processor was produced in large numbers by highly automated processes, so unit cost was low. Single-chip processors increase reliability as there are many fewer electrical connections to fail. As microprocessor designs get faster, the cost of manufacturing a chip (with smaller components built on a semiconductor chip the same size) generally stays the same.

The internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the microprocessor. The complexity of an integrated circuit is bounded by physical limitations of the number of transistors that can be put onto one chip, the number of package terminations that can connect the processor to other parts of the system, the number of interconnections it is possible to make on the chip, and the heat that the chip can dissipate. Advancing technology makes more complex and powerful chips feasible to manufacture.

A minimal hypothetical microprocessor might only include an arithmetic logic unit (ALU) and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR. Each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation (zero value, negative number, overflow, or others). The control logic section retrieves instruction operation codes from memory, and initiates whatever sequence of operations of the ALU requires to carry out the instruction. A single operation code might affect many individual data paths, registers, and other elements of the processor.

As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip. The size of data objects became larger; allowing more transistors on a chip allowed word sizes to increase from 4- and 8-bit words up to today's 64-bit words. Additional features were added to the processor architecture; more on-chip registers sped up programs, and complex instructions could be used to make more compact programs. Floating-point arithmetic, for example, was often not available on 8-bit microprocessors, but had to be carried out in software. Integration of the floating point unit first as a separate integrated circuit and then as part of the same microprocessor chip, sped up floating point calculations.

Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary. Instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. While this required extra logic to handle, for example, carry and overflow within each slice, the result was a system that could handle, say, 32-bit words using integrated circuits with a capacity for only four bits each.

With the ability to put large numbers of transistors on one chip, it becomes feasible to integrate memory on the same die as the processor. This CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Processor clock frequency has increased more rapidly than external memory speed, except in the recent past, so cache memory is necessary if the processor is not delayed by slower external memory.

After the integrated circuit, the only place to go was down - in size, that is. Large scale integration (LSI) could fit hundreds of components onto one chip. By the 1980's, very large scale integration (VLSI) squeezed hundreds of thousands of components onto a chip. It also increased their power, efficiency and reliability.

After 1971 the fourth generation computers were built. The fourth generation computers were the extension of third generation technology. The fourth generation computers emerged with development of the VLSI (Very Large Scale Integration).With the help of VLSI technology microprocessor came into existence. The computers were designed by using microprocessor, 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 computers became more powerful, compact, reliable and affordable. As a result, they give rise topersonal computer (PC) revolution.

For the first time in 1981 IBM introduced its computer for the home user and in 1984 Apple introduced the Macintosh Microprocessor. 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.

As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.

Hardware Technologies of Fourth Generation Computers

·      ICs with VLSI technology

·      Microprocessor; semi-conductor memory

·      Large capacity hard disk as in-built secondary storage

·      Magnetic tapes and floppy disks as portable storage media

·      Supercomputer based on parallel vector processing and symmetric multiprocessing technologies

·      Spread of high speed computer networks

Software Technologies of Fourth Generation mputers

·      Operating systems for PCs with GUI and multiple windows on a single terminal screen

·      Multiprocessing OS with concurrent programming languages

·      Object-oriented design and programming

·      PC, network-based and supercomputing application

Characteristics

1) The fourth generation computers have microprocessor-based systems.

2) They are the cheapest among all the computer generation.

3) The speed, accuracy and reliability of the computers were improved in fourth generation computers.

4) Many high-level languages were developed in the fourth generation such as COBOL, FORTRAN, BASIC, PASCAL and C language.

5) A Further refinement of input/output devices was developed.

6) Networking between the systems was developed.

7) It is totally general purpose machine.

8) It is easier to produce commercially

9) It is easier to upgrade.

10) Rapid software development is possible in this generation.

Example

IBM 4341, DEC 10, STAR 1000, CRAY-1, CRAY-2, VAX 9000, PUP 11 and APPLE II are the examples of fourth generation computers.

Fifth Generation Computers: Artificial Intelligence (1989-present)

Artificial intelligence (AI) is the intelligence exhibited by machines or software. It is an academic field of study which studies the goal of creating intelligence, whether in emulating human-like intelligence or not.

The computers of fifth generation are majorly based upon ULSI. Ultra large-scale integration (ULSI) is the process of integrating or embedding millions of transistors on a single silicon semiconductor microchip. ULSI technology was conceived during the late 1980s when superior computer processor microchips, specifically for the Intel 8086 series, were under development. ULSI is a successor to large-scale integration (LSI) and very large-scale integration (VLSI) technologies but is in the same category as VLSI.

ULSI was designed to provide the greatest possible computational power from the smallest form factor of microchip or microprocessor dye. This was achieved by embedding and integrating integrated circuits (IC), which were formed with transistors and logic gates. The close placement and design architecture enabled faster resolution of tasks and processes. However, even though VLSI now contains more than millions of transistors, any IC or microchip with more than one million transistors is considered a ULSI implementation.

Intel 486 and the Pentium series of processors were built on ULSI principles.

Fifth generation computers are in developmental stage which is based on the artificial intelligence. The goal of the fifth generation is to develop the device which could respond to natural language input and are capable of learning and self-organization. Quantum computation and molecular and nanotechnology will be used in this technology. So we can say that the fifth generation computers will have the power of human intelligence.

Fifth generation computing devices, based on artificial intelligence, 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.

Hardware Technologies of Fifth Generation Computers

·      ICs with ULSI technologies

·      Larger capacity main storage and Hard disk with raid support

·      Optical disk as portable read-only storage media

·      Notebooks, powerful desktop PCs and workstations

·      Powerful servers

·      Internet

·      Cluster computing

Software Technologies of Fifth Generation Computers

·      Micro-kernel based, multithreading, distributed OS

·      Parallel programming libraries like MPI and PVM

·      Java

·      World wide web

·      Multimedia, internet application

·      More complex supercomputing application

Characteristics

1) The fifth generation computers will use super large scale integrated chips.

2) They will have artificial intelligence.

3) They will be able to recognize image and graphs.

4) Fifth generation computer aims to be able to solve highly complex problem including decision making, logical reasoning.

5) They will be able to use more than one CPU for faster processing speed.

6) Fifth generation computers are intended to work with natural language.

7) There will be more portable computers.

8) It is totally general purpose machine.

9) Rapid software development is possible.

Example

IBM Notebook, Pentium PCs series, SUN Workstations, IBM SP/2, SGI Origin 2000, PARAM 1000 are examples of fifth generation of computers.