Generation of computer
A Brief History of the Computer:
The history of the computer can be divided into six generations each
of which was marked by critical conceptual advances.
The Mechanical Era (1623-1945)
The idea of using machines to solve mathematical problems ca
n be traced at least as far back as the early 17th century, to mathematicians who designed and implemented calculators that were capable of addition, subtraction, multiplication, and division.
Among the earliest of these was Gottfried Wilhelm Leibniz (1646-1716), German philosopher and co-founder (with Newton) of the calculus. Leibniz proposed the idea that mechanical calculators (as opposed to humans doing arithmetic ) would function fastest and most accurately using a base-two, that is, binary system.
Leibniz actually built a digital calculator and presented it to the scientific authorities in Paris and London in 1673. His other great contribution to the development of the modern computer was the insight that any proposition that could be expressed logically could also be expressed as a calculation, "a general method by which all the truths of the reason would be reduced to a kind of calculation"(Goldstine 1972).
Inherent in the argument is the principle that binary arithmetic and logic were in some sense indistinguishable: zeroes and ones could as well be made to
represent positive and negative or true and false. In modern times this would result in the understanding that computers were at the same time calculators and logic machines.The first multi-purpose, i.e. programmable, computing device was probably Charles Babbage's Difference Engine, which was begun in 1823 but never completed. A more
ambitious machine was the Analytical Engine. It was designed in 1842, but
unfortunately it also was only partially completed by Babbage.
That the modern computer was actually capable of doing something
other thannumerical calculations is probably to the credit of George B
oole (1815-1864), towhom Babbage, and his successors, were in deep debt. By showing that formal logic could be reduced to an equation whose results could only be zero or one, he made itpossible for binary calculators to function as logic machines (Goldstine 1972).
First Generation Electronic Computers (1937--1953)
Three machines have been promoted at various times as the first electronic computers.These machines used electronic switches, in the form of va
cuum tubes, instead ofelectromechanical relays. Electronic components had one major benefit, however: they could "open" and "close" about 1,000 times faster than mechanical switches.
A second early electronic machine was Colossus, designed by Alan Turing for the British military in 1943. This machine played an important role
in breaking codes used by the German army in World War II. Turing's main contribution to the field of computer science was the idea of the "Turing machine," a mathematical formalism,indebted to George Boole, concerning computable functions.The machine could be envisioned as a binary calculator with aread/write headinscribing the equivalent of zeroes and ones on a movable and indefinitely long tape.
The Turing machine held the far-reaching promise that any problem
that could be calculated could be calculated with such an "automaton," a
nd, picking up from Leibniz, that any proposition that could be expressed logically could, likewise, be expressed by such an "automaton."
The first general purpose programmable electronic computer was
the Electronic Numerical Integrator and Computer (ENIAC), built by J. Presper Eckert and John V.Mauchly at the University of Pennsylvania. The machine wasn't completed until 1945,but then it was used extensively for calculations during the design of the hydrogen bomb.The successor of the ENIAC, the EDVAC project was significant as an example of the power of interdisciplinary projects that characterize modern computational science.
By recognizing that functions, in the form of a sequence of instructions for a
computer, can be encoded as numbers, the EDVAC group knew the instr
uctions couldbe stored in the computer's memory along with numerical data
(a "von NeumannMachine").The notion of using numbers to represent functions was a key step used by Gödel in his incompleteness theorem in 1937, work with which von Neumann, as a logician,was quite familiar. Von Neumann's own role in the development of the modern digital
computer is profound and complex, having as much to do with brillia
nt administrative leadership as with his foundation insight that the instructi
ons for dealing with data,that is, programming, and the data themselves, were both expressible in binary terms to the computer, and in that sense indistinguishable one from the other. It is that insight which laid the basis for the "von Neumann machine," which remains the
principal architecture for most actual computers manufactured
today.
Second Generation Computers (1954--1962)
The second generation saw several important developments at all
levels of computer system design, from the technology used to build the basic circuits to the programming languages used to write scientific applications.Memory technology was based on magnetic cores which could be accessed in randomorder, as opposed to mercury delay lines, in which data was stored as an acoustic wave that passed sequentially through the medium and could be accessed only when the data moved by the I/O interface.During this second generation many high level programming languages were introduced, including FORTRAN (1956), ALGOL (1958), and COBOL (1959).
Important commercial machines of this era include the IBM 704and its successors,the 709 and 7094. The latter introduced I/O processors for better throughput between I/O devices and main memory.
Third Generation Computers (1963--1972)
The third generation brought huge gains in computational power. Innovat
ions in this era include the use of integrated circuits, or ICs (semiconduc
tor devices with several transistors built into one physical component), semiconductor memories starting to be used instead of magnetic cores, microprogramming as a technique for efficiently designing complex processors, the coming of age of pipelining and ot her forms of
parallel processing, and the introduction of operating systems and time-sharing.
Fourth Generation Computers (1972--1984)
The next generation of computer systems saw the use of large s
cale integration (LSI --1000 devices per chip) and very large scale integration (VLSI-- 100,000 devices per chip) in the construction of computing elements. At this scale entire processors will fit onto a single chip, and for simple systems the entire computer (processor, main memory, and I/O controllers) can fit on one chip. Gate delay s dropped to about 1ns per gate.
Two important events marked the early part of the third generation: the development of the C programming language and the UNIX operating system,both at Bell Labs. In 1972, Dennis Ritchie, seeking to meet the design goals of CPL and generalize Thompson's B, developed the C language.
Fifth Generation Computers (1984--1990)
The development of the next generation of computer systems is chara
cterized mainly by the acceptance of parallel processing. The fifth genera
tion saw the introduction of machines with hundreds of processors that could all be working on different parts of a single program. The scale of integration in semiconductors continued at an incredible pace --- by 1990 it was possible to build chips with a million components --- and semiconductor memories became standard on all computers.
Sixth Generation Computers (1990--)
Many of the developments in computer systems since 1990 reflect
Gradual improvements over established systems, and thus it is hard to
claim they represent a transition to a new "generation", but other developments will prove to be significant changes.One of the most dramatic changes in the sixth generation will be the explosive growth of wide area networking. Network bandwidth has expanded tremendously inthe last
few years and will continue to improve for the next several years