The
first machine using this concept was the EDSAC (Electronic
Delayed Storage Automatic Computer), which was built at Cambridge
University in England in 1949. At the same time, Mauchly and Eckert,
the original builders of the ENIAC, contiuned their pioneering efforts
and produced their own stored-program computer, the EDVAC, in
1952. Shortly thereafter, they formed a company and sold their first
computer, UNIVAC 1, to the Census Bureau.
First-generation
computers (1951-1959)
The
UNIVAC 1 was the first of what have come to be called first-generation
machines. These are typified by using vacuum tubes, by performing
slowly (about 1,000 instruction per second),and having a memory capacity
of about 16,000 characters of data (the equivalent of about four single-spaced
typed pages). It was during this period that the precedent was set
for computers to be developed only by large corporations because of
the enormous costs involved.
Second-generation
computers (1959-1964)
The
era of the first-generation computers ended in 1959 with the replacement
of vacuum tubes by transistors. Development of the transistor by three
Bell Laboratories scientists, John Bardeen, Houser Brattan, and William
Shickley, revolutioned the world. The transistor accomplishes everything
a vacuum tube does, uses far less power, and occupies approximately
1/100th of the space. It is also far more reliable and requires no
warm-up time. Second-generation computers used transistors rather
than tubes, thus increasing their reliability and computational speed,
and reducing their volume, cost, and power consumption.
Third-generation
computers (1964-1971)
Third-generation
computers are attributted to the invention of the integrated circuit,
or IC. Integrated circuits allow many components to exist on a single
small chip. Thus, what had previously been a box full of transistiors
and other electronic parts making up the "brain" of the
computer could now be packed into an area about 1/4-inch square, known
as a chip. IC's are even more reliable than transistors, are cheap
to produce, are compact, and use virtually no power at all compared
to previous technologies. One of the most important products developed
from the integrated technology was the microprocessor. This
was a comoputer's "brain" or central processor, completley
contained on a single chip the size of a matchbox. With so much power
residing on such a small chip, it became possible to build entire
computers around it. Thus, microcomputers and minicomputers were born.
Fourth-generation
computers (1971 - present)
Once
the integrated circuit became a reality, the story of further developments
centers around how many circuits could be packed on a single silicon
chip. Large-scale integration (LSI), for example, made possible the
pocket calculator and the digital watch. Advances in microprocessor
technology were paralleled by the development of memory chips, that
is, chips designed to hold all the zeros and ones needed to express
commands in programs. The microprocessor would direct information
to be stored in these chips, as well as to be drawn from the chips
in the course of executing the programs.
Fifth-generation
computers (Present and Beyond)
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.
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The
limitations of the ENIAC became obvious very quickly, particularly
the fact that to change its function required rewiring a substantial
part of the machine, which was a slow process. The solution to this
problem is usually attributed to John von Neumann who came up with
the "stored-program" concept, in which the sequence of instructions
to be performed (called a program) could be entered in much
the same way as data stored in the computer to be stored when needed.
Being able to do this made rewiring the computer each time unnecessary.