Chapter 3: Sketch of the Analytical Engine (1843), L. F. Menabrea, with Notes by the Translator, Ada Augusta, Countess of Lovelace

This is my summary of Chapter 3of Harry R. Lewis’ book Ideas That Created the Future: Classic Papers of Computer Science which talks about the Sketch of the Analytical Engine conceived by Charles Babbage and Ada Lovelace in 1837.

In 1837, Charles Babbage an English polymath along with his assistant Ada Lovelace worked on and proposed a sketch of a general-purpose computer for what was known as Analytical Engine. Up until that point, various inventors had proposed calculators which would mechanically compute inputs sent by users. What made the Analytical Engine different from calculators was its ability to be programmed and make decisions, thus, the Analytical Engine could reasonably be called the first proposed general-purpose computer.

Around that time calculators could perform the 4 basic arithmetic operations, namely -: Addition, Subtraction, Multiplication, and Division. And in essence, they were just 2 operations since multiplication and division were a result of a series of additions and subtractions. Pascal’s mechanical calculator could take in only 2 inputs at a time. So if we were to carry out an operation like — “100 + 400–500 * 600”. The user would first have to recognize the order of operation(In this case to perform 500*600 first). Then store it separately. Re-compute over and over again till the expression got reduced to a single answer. As we see, besides being limited in their functionality, calculators also required continuous human activity to feed them inputs. Which was a potential source for errors to creep in and was also not time efficient. Thus Babbage not only wanted a machine capable of executing arithmetic operations but also performing analysis. So to perform analysis the machine had to also be capable of understanding the correct distribution of the computed quantities and be able to execute those numerical computations on its own without any human interference. In the above example, it would mean that the machine would recognize that 500*600 would need to be calculated first.

Babbage’s Analytical Engine makes use of vertical columns consisting of stacked circular discs which are pierced through the center. Each disc represents numbers from 0–9 and stacks of discs can be used to either represent greater digit numbers or store information. For example, in Fig.1 we have a vertical column, C1, which has 6 discs.

Fig.1 Shows a column named C1 with 6 discs and a red line running through the middle which is its reference line.

Now, if we were to take one of the discs and look at it from the top we would see the disc as follows( Fig.2 ) -:

Fig.2 Shows a disc numbered 0–9

The reference line is used to read out the value which is currently being held at that particular disc. Now for different operations, there are different sets of discs that are involved. Thus identifying the performing operation and the variables which would be involved becomes crucial. To understand how the Analytical Engine does this identification without human intervention, understanding the workings of a Jacquard Machine is important. The Jacquard Machine was a device fitted to a loom that simplified the production of large-scale complex patterns on textiles. It made use of punch cards onto which the user would punch in a pattern and the machine would then go on to design complex patterns on textiles based on it.

Babbage had stated rigid accuracy, labor savings, and better allocation of intellectual resources as reasons to pursue such a device. Although he was never able to complete his Analytical Engine due to conflicts with his Chief engineer and inadequate funding yet his write-ups did lay a blueprint for further generations.

References

1. Sketch of the Analytical Engine (1843), L. F. Menabrea, with Notes by the Translator, Ada Augusta, Countess of Lovelace
2. Ideas That Created the Future: Classic Papers of Computer Science, Harry R. Lewis