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Computer Generations
0 -
Mechanical / Electromechanical
1 - Vacuum tube
Mechanical
Mechanical
computers were built with trains of gears, much like clocks. Typically, they
used decimal arithmetic, and each gear or wheel had ten positions. The hardest
part of designing such a machine was to get the carry to propogate cleanly from
one digit to the next (so that there wouldn't be any ambiguous, half visible,
numbers showing in the display windows). The other difficulty was that the sheer
amount of complexity of a large calculator, together with the friction of all of
the gears, made construction very difficult prior to the advent of modern
machining technology.
Storage in a mechanical computer was by the
position of the gears. In the later electromechanical machines, relays were able
to store some of the machine's state. The program, however, was always stored in
a separate medium, typically a punched paper card or tape. Some analog
mechanical computers could be programmed by changing the gear train, but this
was really just equivalent to changing parameters to the program, since they
generally just computed one type of function (e.g. differential
equations).
Relays work on the principle that a voltage is applied to a
coil, driving a magnetic rod (solenoid) outward so that a hinged or flexible
electrical contact is forced to touch a fixed contact, thus closing a circuit.
We thus have an electrically controlled switch.
The significance of the
electrically controlled switch is that information (the state of switch in one
place) can be transmitted over significant distances without loss, and without
interference. In a mechanical system, carrying the state of one wheel to another
at a distance involves long shafts and often extra gears to allow the shafts to
bypass other shafts.
Also of major significance is that the relay is more
naturally used with a binary number system (rather than decimal), because of the
on/off nature of circuits.
Mechanical
· Edmund Gunter's scale (1624)
· Wilhelm Schickard's calculator (1624)
· Blaise Pascal's "box" (1643)
· Gottfried Wilhelm Liebniz's calculator (1685)
· Variations of Liebniz' calculator
· Joseph Jacquard loom (1805)
· Charles Thomas Arithmometer (1820
Gunter's
scale, based on Napier's bones, was the first slide rule. Multiplication and
division could be done using sliding sticks insribed with a logarithmic
scale.
Schickard's
calculator was destroyed in a fire and never rebuilt -- we know of it only
through a letter written to Johannes Kepler. If Schickard's claims are true, it
was much more sophisticated than Pascal's box.
Pascal's
box could add and subtract amounts of money. He invented it to aid his
father, a tax collector. Note that even today, taxes are still a major
application area for computers. Pascal's box was such a sensation that people
even made and sold non-working replicas as showpieces. Several copies still
exist in museums.
Liebniz's
calculator was much like Pascal's but could also multiply. Division required
a long sequence of steps. Interestingly, Liebniz's goal was to reduce thought to
a logical abstraction that could be performed automatically -- although he
didn't use the term, he was actually seeking to create artificial
intelligence.
Lepine (1725), Hillerin (1730), Pereire(1751), Earl
Stanhope (1775) etc. built calculators similar to those of Pascal and Liebniz,
with minor improvements.
Jaquard's loom is programmable by feeding it a
chain of cards with holes punched in. The loom can weave any pattern, including
a portrait of the inventor. Although it doesn't calculate, it is the first
programmable machine.
The Thomas Arithmometer, the first commercially
manufactured mechanical calculator, remained in production until 1926.
Mechanical
· Charles Babbage's difference and analytical engines (1833, 1837, 1853)
· Herman Hollerith's census tabulator (1890)
· Vannevar Bush's Differential Analyzer (1931)
· Konrad Zuse's electromechanical calculators (1936, 1939)
· Howard Aiken's (Harvard) Mark I (1944)
Babbage's
difference engine was an automated calculator for numerical tables.
The
analytical engine was the first programmable computer, using punched cards for
storing instructions. Babbage got the idea from the Jacquard automatic loom.
Neither of Babbages engines were ever completed. But, in 1853, a difference
enginebased on Babbage's design was built by George and Edward Scheutz in
Later
on Herman Hollerith would use the same sort of cards as Babbage, but for
entering data into a tabulating machine he built for the 1890 census; his
company would eventually become IBM. The tabulator was also novel in its use of
electricity to carry the information from the cards to the
calculator.
Bush's Differential Analyzer was an electromechanical analog
computer for computing differential equations. Programming was limited, and was
accomplished by replacing gears in the drive mechanism.
Zuse's
electromechanical calculators used relays and were very similar in concept to
Babbage's analytical engine. They were the first working programmable computers.
Zuse also had a plan for an electronic computer using 1500 vacuum tubes.
Unfortunately, most of Zuse's early work was destroyed in World War II, although
he continued to build computers after the war. Later in
life he became a painter.
Howard
Aiken's Mark I was a 52 x 8 feet sized programmable calculator. It used decimal
arithmetic, and was built largely from parts used in commercial tabulating
machines. Addition took 0.3 seconds, multiplication took 6 seconds.
Pictures of some other
electromechanical computers.
Vacuum
Tube
A
vacuum tube is, reasonably enough, a sealed glass tube containing a vacuum in
which are present several electronic elements: the cathode, anode, grid, and
filament. When the cathode and anode are heated by the filament, and a voltage
is applied across them, current flows between the cathode and anode. If a grid
is inserted between them, the flow can be controlled by changing the grid
between a positive and negative voltage.
The grid voltage can be quite
small, and the plate voltages can be quite high, thus providing an amplifying
capability. More importantly for computers, switching the grid voltage causes
the tube to act as a switch with respect to the plates. Thus, we have an
electronically controlled switch that is much faster than a relay.
A type
of vacuum tube also served as a popular storage mechanism, the Cathode Ray Tube
(CRT). Other memory devices used during the period include mercury or glass
delay lines, and magnetic core memory.
Vacuum tubes, however, are large,
require a lot of power, and produce a lot of waste heat. In fact, for one rather
large vacuum tube machine, it was once estimated that if its four
turbine-powered air conditioners were to fail, the heat buildup in 15 minutes
would be sufficient to melt the concrete and steel building containing it (of
course, it would simply catch fire and stop working long before that). It has
also been estimated that if a modern computer were built with vacuum tubes, it
would be the size of the
Vacuum
Tube
· Atanasoff's machine (1940)
· COLOSSUS (1943)
· ENIAC (1946
· MADM (1948
· EDVAC and EDSAC (1949
John Atanasoff developed an
electronic switch based on vacuum tubes, and used this in a special purpose
computer that had capacitors as memories (essentially the same principle as
modern dynamic RAM).
The COLOSSUS machines were developed by British
Intelligence during WW II to crack coded messages. They also used vacuum tubes
as logic elements. Much of their design remains secret.
ENIAC (Electronic
Numerical Inegrator and Calculator) was developed at the Moore School of
Engineering as a specialized programmable computer for computing ballistics
tables for the Army. It was programmed by changing wires in patch panels, and
flipping switches. John von Neumann became involved with ENIAC and saw the need
for storing the program in the machine itself, resulting in the EDVAC
(Electronic Discrete Variable Calculator) design.
The Manchester
Automatic Digital Machine (MADM) was the first machine built with a stored
program, but it was really just for testing a new memory device.
EDSAC
(Electronic Delay Storage Automatic Calculator) was based closely on the EDVAC
design and was the first true stored program computer to become operational. It
used an ultrasonic glass delay line for a memory.
Vacuum
Tube
· UNIVAC (1951)
· IAS machine (1952)
· JOHNNIAC (1953)
· Whirlwind (1953)
· IBM 701 (1953)
· IBM 709 (1958)
UNIVAC, built by Presper
Eckert and John Mauchley, from the
Von
Neumann left the Moore School for the Institute for Advanced Studies at
Princeton, where he became involved in another computer design (known as the IAS
machine), which was also based on EDVAC. The JOHNNIAC,
named in honor of von Neumann, was an IAS-like machine built by the Rand
Corporation in
The
Whirlwind, built at MIT, is notable mostly for the development of magnetic core
memory, which would eventually replace CRT and delay line storage during the
1960's.
The IBM 701 was their first commercial computer and grew out
their work with Harvard on the last successor to the Mark I (the Mark IV). The
701 was developed to directly compete with the UNIVAC.
The IBM 709 was the last
of the major vacuum tube computers. It was a faster 704, which had 4K 36- bit
words of core memory. During this period, IBM also sold a model 650, which had a
magnetic drum memory, but was low enough in cost that many were sold to
universities -- it was the basis for the first user's community.
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