A BRIEF HISTORY OF COMPUTERS
The First Generation: Vacuum
Tubes ENIAC The ENIAC (Electronic Numerical Integrator and Computer), designed
by and constructed under the supervision of John Mauchly and John Presper
Eckert at the University of Pennsylvania, was the world's first general-purpose
electronic digital computer.
The project was a response to U.S. wartime needs during World War II. The Army's Ballistics Research Laboratory (BRL), an agency responsible for developing range and trajectory tables for new weapons, was having difficulty supplying these tables accurately and within a reasonable time frame.
The new weapons and artillery were useless
to gunners without these firing tables. The BRL employed more than 200 people
who, using desktop calculators, solved the necessary ballistics equations.
Preparation of the tables for a single weapon would take one person many hours,
even days.
Mauchly, a professor of electrical engineering at the University of Pennsylvania, and Eckert, one of his graduate students, proposed to build a general-purpose computer using vacuum tubes for the BRE's application. In 1943, the Army accepted this proposal, and work began on the ENIAC.
The resulting machine was enormous,
weighing 10 tons, occupying 1500 square feet of floor space, and containing
more than 18.000 vacuum tubes When operating, it consumed 140 kilowatts of
power. It was also substantially faster than any electromechanical computer,
being capable of 5000 additions per second.
The ENIAC was a decimal rather than a binary machine. That is, numbers were represented in decimal form and arithmetic was performed in the decimal system. Its memory consisted of 20 "accumulators" each capable of holding a 10-digit decimal number. A ring of 10 vacuum tubes represented each digit. At any time, only one vacuum tube was in the ON state, representing one of the 10 digits.
The major drawback
of the ENIAC was that it had to be programmed manually by setting switches and
plugging and unplugging cables.
The ENIAC was completed in 1946,
too late to be used in the war effort. Instead, its first task was to perform a
series of complex calculations that were used to help determine the feasibility
of the hydrogen bomb. The use of the ENIAC for a purpose other than that for
which it was built demonstrated its general-purpose nature. The ENIAC continued
to operate under BRL management until 1955 when it was disassembled.
The von Neumann Machine The task of entering and altering programs for the ENIAC was extremely tedious. The programming process could be facilitated if the program could be represented in a form suitable for storing in memory alongside the data. Then, a computer could get its instructions by reading them from memory, and a program could be set or altered by setting the values of a portion of memory.
This idea, known
as the stored-program concept, is usually attributed to the ENIAC designers,
most notably the mathematician John von Neumann, who was a consultant on the
ENIAC project. Alan Turing developed the idea at about the same time. The first
publication of the idea was in a 1945 proposal by von Neumann for a new
computer, the EDVAC (Electronic Discrete Variable Computer).
In 1946, von Neumann and his
colleagues began the design of a new stored-program computer, referred to as
the IAS computer, at the Princeton Institute for Advanced Studies the IAS
computer, although not completed until 1952, is the pro- to type of all
subsequent general-purpose computers Figure 2.1 shows the general structure of
the IAS computer. It consists of
A main memory, which stores both
data and instructions an arithmetic and logic unit (ALU) capable of operating
on binary data. A control unit, which interprets the instructions in memory and
causes them to be executed
Input and output (I/O) equipment operated by the control unit
2.2 First: Because the device is
primarily a computer, it will have to perform the elementary operations of
arithmetic most frequently. These are addition, subtraction, multiplication,
and division. It is therefore reasonable that it should contain specialized
organs for just these operation slag
It must be observed, however,
that while this principle as such is probably sound, the specific way in which
it is realized requires close scrutiny… At any rate, a central arithmetical
part of the device will probably have to exist, constituting the first specific
part: CA.
2.3 Second: The logical control of the device, that is, the proper sequencing of its operations can be most efficiently carried out by a central control organ. If the device is to be elastic, that is, as nearly as possible all-purpose, then a distinction must be made by tween the specific instructions given for and defining a particular problem, and the general control organs which see to it that these instructions-no matter what they are-are carried out.
The for me must be stored
in some way; the latter is represented by definite operating parts of the
device. By central control we mean this latter function only, and the organs
which perform it form the second specific part: CC. 2.4 Third: Any device which
is to carry out long and complicated sequences of operations (specifically of
calculations) must have a considerable memory…
(b) The instructions which govern
a complicated problem may constitute considerable material, particularly so, if
the code is circumstantial (which it is in most arrangements). This material must
be remembered... At any rate, the total memory constitutes the third specific
part of the device.
2.6 The three specific parts CA,
CC (together C), and M correspond to the associative neurons in the human
nervous system. It remains to discuss the equivalents of the sensory or
afferent and the motor or efferent neurons. These are the input and output
organs of the device...
The device must be endowed with the ability to maintain input and output (sensory and motor) contact with some specific medium of this type. The medium will be called the devices outside recording medium: R… 2.7 Fourth: The device must have organs to transfer... information from R into its specific parts C and M. These organs form its input, the fourth specific part: I.
It will be seen that it is best to make all transfers from R (by 1) into M and never directly from C… 2.8 Fifth: The device must have organs to transfer...from its specific parts C and M into R. These organs form its output, the fifth specific part: O. It will be seen that it is again best to make all transfers from M (by O) into R, and never directly from C...