The Analytical Engine of Charles Babbage

Introduction:

Charles Babbage, a great Mathematician, philosopher and computer scientist who was the first to originate the idea of a programmable computer in his years of developing new systems came up with the idea and design of the Analytical Engine, a general purpose computer in the 19th century. During his time he failed to actually build the system due to financial, political, and legal issues. The system was actually built some years ago while its idea was anticipated almost a century ago.

In Babbage’s times there was a really high error rate in the calculation of math tables, when Babbage planned to find a new method that could be use to make it mechanically, removing the human error factor. The idea came upon him very early when he was actually inspired by the existing works on calculating machines produced by famous mathematicians like W. Schickard, B.Pascal, and G. Leibnitz.

The different factors which actually influenced Charles Babbage into designing such machines was that he disliked untidiness and erroneous results and that we was very well equipped with logarithmic functions and logarithmic tables. Finally he came up with an innovative idea of designing a calculating machine and he further discussed his plans and techniques with Sir Henry Davy in the late 1822.The idea of the Analytical Engine came in 1838 shortly after the collapse of the project on Difference Engine.[1]He was 42 at that time.

Phases of development:

The design of the Analytical Engine took place in two phases. By mid 1836 a workable design of the Analytical Engine was evolved. Then a major revision of the design took place in 1837. In the meantime Babbage did not have any plans of developing the engine in actual. What he was mainly interested was of the actual refinement and evolving more diverse ideas regarding the engine. Infact, the main idea of the engine at that time was the refinement and elaboration of the plans originally formulated in 1837. After this Babbage ceased to develop the plans for the engine .Later on at the time of his death, a substantial model of the machine was in the process of development. Hence very little was known from the creator itself about the machine. In 1837 Babbage wrote a general description of the engine but very little was known until recent times. Babbage however kept extensive private notes of the design itself. Later he presented a paper which intended to show that an automatic computing machine could be built using mechanical devices and that was the very essence of this machine.

Basic Design Concept, working principle and components:

The Analytical Engine basically consists of two parts: a) The Store, in which all variables are operated on and b) The Mill unto which the operated components are to be brought always for operation.

Babbage decided to use decimal and sign-and-magnitude number representations. A wheel rotating on a shaft was the concept originally adopted since it was as easy to represent 10 numbers as was 100 or 2. It was built on a series of horizontal plates separating the figure wheels on the various axes. A collection of figure wheels on the axis corresponds to a register on a modern computer. The space between two wheels is called a cage. The bottom plate holds the units figure, the next above tens, then hundreds and so on. [2]

All the numbers in the Engine are of 40 digits, and there are 40 cages and 40 figure wheels on each axis. The figure wheel can be rotated by the 10 wheels to stand on any of the 10 positions.

The figure alongside represents the basic process of addition. A digit is given off by the right figure wheel to the left figure wheel. If the original position of the receiving figure wheel is not 0 it will come to a standstill at the original sum of the two digits .The process then takes place simultaneously for all the other digits in succession. Hence we present a brief summary of the components required:

a) The 3 figure and 3 carriage axes.

b) The 10 Table Figure Axes: speeds up multiplication and division by providing multiples of factors and divisors.

c) Digit Counting Apparatus: counts the number of digits in a given column.

d) Selecting Apparatus: selects the multiples indicated by the successive digits of the multiplier from the Table Figure Axis.

e) Barrels: causes the studs to push levers which execute different functions within the Mill.

f) Reducing Apparatus: rotate the barrel so as to make it pass over any number of vertical columns.

g) Operation and Combinatorial Cards.

Conclusion:

The description presented here is very basic and introductory. More analysis of this machine will show the extensiveness and the sophisticated mechanics actually implemented. Infact, the sophistication of this machine is very remarkable, more than it is actually supposed to be, as it is evident in the design at the level of microprogramming of basic arithmetical operations.

The design of the Analytical was later on carried to a considerable state of perfection and it forms the building blocks in the design of modern computers. In the History of Computers, the study of the design of this machine provides a very rare opportunity to study the basics of computing techniques. The design of Babbage’s original concepts was carried out later after his death but there was no effect of modern developments in his design.[3]

In one view of the Analytical Engine it is infact remarkable that it has a lot of similarities with that of the modern computer. Although the technologies used in modern times and that of Babbage’s time almost two centuries ago it is infact very surprising to see the similarity in the jobs done. The modern computers have just implemented the basic idea of computational methods as used in the Analytical Engine. The increasing sophistication and the choice of mechanism and also the idea of implementing mechanics into computing basics can be though of as the stepping stone in the design of modern gadgets.

References:

Brian Randell, The Origins of Digital Computers, Berlin, Springer Verdall.

A.G. Bromley, The Functional Algorithms and control of Charles Babbage’s Analytical Engine, 1980.

Bruce Collier, The Calculating Machines of Charles Babbage, Thesis, Harvard Univ.

Babbage History and Analytical Engine:

http://ei.cs.vt.edu/~history/Babbage.html

[1] For a detailed account of Babbage’s involvement on calculating machines and Computers see Colier and Hyman series.

[2] The internal operations like multiplication and division were controlled by special operating units called “barrels”

[3] Babbage’s papers were not subject to any detailed examination until 1969 and hence cannot have influenced the design of Modern Computing.