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					              First Generation Computers.
The first generation of computers is said by some to have started in
1946 with ENIAC, the first 'computer' to use electronic valves (ie.
vacuum tubes). Others would say it started in May 1949 with the
introduction of EDSAC, the first stored program computer. Whichever,
the distinguishing feature of the first generation computers was the
use of electronic valves.
My personal take on this is that ENIAC was the World's
first electronic calculator and that the era of the first generation
computers began in 1946 because that was the year when people
consciously set out to build stored program computers (many won't
agree, and I don't intend to debate it). The first past the post, as
it were, was the EDSAC in 1949. The period closed about 1958 with the
introduction of transistors and the general adoption of ferrite core
memories.
OECD figures indicate that by the end of 1958 about 2,500 first
generation computers were installed world-wide. (Compare this with
the number of PCs shipped world-wide in just the third quarter of
2006, quoted as 59.1 million units by research company Gartner).
Two key events took place in the summer of 1946 at the Moore School
of Electrical Engineering at the University of Pennsylvania. One was
the completion of the ENIAC. The other was the delivery of a course
of lectures on "The Theory and Techniques of Electronic Digital
Computers". In particular, they described the need to store the
instructions to manipulate data in the computer along with the data.
The design features worked out by John von Neumann and his colleagues
and described in these
lectures laid the foundation
for the development of the
first generation of
computers. That just left the
technical problems!
One of the projects to
commence in 1946 was the
construction of the IAS
computer at the Institute of
Advanced Study at Princeton.
The IAS computer used a
random access electrostatic
storage system and parallel
binary arithmetic. It was
very fast when compared with
the delay line computers,
with their sequential
memories and serial
arithmetic.
The Princeton group was liberal with information about their computer
and before long many universities around the world were building
their own, close copies. One of these was the SILLIAC at Sydney
University in Australia.
I have written an emulator for SILLIAC. You can find it here, along
with a link to a copy of the SILLIAC Programming Manual.


First Generation Technologies
In 1946 there was no 'best' way of storing instructions and data in a
computer memory. There were four competing technologies for providing
computer memory: electrostatic storage tubes, acoustic delay lines
(mercury or nickel), magnetic drums (and disks?), and magnetic core
storage.
A high-speed electrostatic store was the heart of several early
computers, including the computer at the Institute for Advanced
Studies in Princeton. Professor F. C. Williams and Dr. T. Kilburn,
who invented this type of store, described it in Proc.I.E.E. 96,
Pt.III, 40 (March, 1949). A simple account of the Williams tube is
given here.
The great advantage of this type of "memory" is that, by suitably
controlling the deflector plates of the cathode ray tube, it is
possible to redirect the beam almost instantaneously to any part of
the screen: random access memory.
Acoustic delay lines are based on the principle that electricity
travels at the speed of light while mechanical vibrations travel at
about the speed of sound. So data can be stored as a string of
mechanical pulses circulating in a loop, through a delay line with
its output connected electrically back to its input. Of course,
converting electric pulses to mechanical pulses and back again uses
up energy, and travel through the delay line distorts the pulses, so
the output has to be amplified and reshaped before it is fed back to
the start of the tube.
The sequence of bits flowing through the delay line is just a
continuously repeating stream of pulses and spaces, so a separate
source of regular clock pulses is needed to determine the boundaries
between words in the stream and to regulate the use of the stream.
Delay lines have some obvious drawbacks. One is that the match
between their length and the speed of the pulses is critical, yet
both are dependent on temperature. This required precision
engineering on the one hand and careful temperature control on the
other. Another is a programming consideration. The data is available
only at the instant it leaves the delay line. If it is not used then,
it is not available again until all the other pulses have made their
way through the line. This made for very entertaining programming!
A mercury delay line is a tube filled with mercury, with a piezo-
electric crystal at each end. Piezo-electric crystals, such as
quartz, have the special property that they expand or contract when
the electrical voltage across the crystal faces is changed.
Conversley, they generate a change in electrical voltage when they
are deformed. So when a series of electrical pulses representing
binary data is applied to the transmitting crystal at one end of the
mercury tube, it is transformed into corresponding mechanical
pressure waves. The waves travel through the mercury until they hit
the receiving crystal at the far end of the tube, where the crystal
transforms the mechanical vibrations back into the original
electrical pulses.
Mercury delay lines had been developed for data storage in radar
applications. Although far from ideal, they were an available form of
computer memory around which a computer could be designed. Computers
using mercury delay lines included the ACE computer developed at the
National Physical Laboratory, Teddington, and its successor, the
English Electric DEUCE.
A good deal of information about DEUCE (manuals, operating
instructions, program and subroutine codes and so on) is available on
the Web and you can find links to it here.
Nickel delay lines take the form of a nickel wire. Pulses of current
representing bits of data are passed through a coil surrounding one
end of the wire. They set up pulses of mechanical stress due to the
'magnetostrictive' effect. A receiving coil at the other end of the
wire is used to convert these pressure waves back into electrical
pulses. The Elliott 400 series, including the 401, 402, 403 used
nickel delay lines. Much later, in 1966, the Olivetti Programma
101 desk top calculator also used nickel delay lines.
The magnetic drum is a more familiar technology, comparable with
modern magnetic discs. It consisted of a non-magnetic cylinder coated
with a magnetic material, and an array of read/write heads to provide
a set of parallel tracks of data round the circumference of the
cylinder as it rotated. Drums had the same program optimisation
problem as delay lines.
Two of the most (commercially) successful computers of the time, the
IBM 650 and the Bendix G-15, used magnetic drums as their main
memory.
The Massachusetts Institute of Technology Whirlwind 1 was another
early computer and building started in 1947. However, the most
important contribution made by the MIT group was the development of
the magnetic core memory, which they later installed in Whirlwind.
The MIT group made their core memory designs available to the
computer industry and core memories rapidly superceded the other
three memory technologies.

				
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