Shannon's work. The prehistory of Unix part 6

Shannon's work

If you were to ask a group of historians of technology which was the second most important scientist in the Bell Laboratories, it would be difficult to get two equal answers. This institution housed in its different facilities some of the most talented physicists, engineers, mathematicians, specialists in metallurgy and even psychologists. which were key to the company's ambition to extend telephone service throughout the United States.

But when it comes to answering which is the most important, the answer is probably unanimous; Claude shannon. In this series of articles I try as much as possible not to give too many proper names or dates to focus on events. However, it is inevitable to stop at Shannon because, like Newton or Einstein, he created by himself a whole new field of study.

What did Shannon's job consist of?

We had left Claude Shannon, an Engineering and Mathematics graduate student, excited about the possibilities of the differential analyzer. It was a machine that, by combining different positions of the relays, had the ability to solve equations. Shannon proposed the possibility of using Boolean algebra, a relatively new branch of mathematics, to design such devices.

Boolean algebra only supports two variables; 0 and 1 and 3 basic operations:

  • Denied (NOT)
  • Sum (OR)
  • Product (AND)

Shannon related the two possible positions of each relay (off and on) with the two variables (0 and 1). The paper he wrote on the subject is considered the most influential master's thesis in history.

Without being clear about what to do, he collaborated for a time in genetic research, but without losing his interest in the issue of information transmission. Following an article on how to measure and think about the data flow of the sender and receiver, began to speculate on a general theory that encompasses the different media.

Faced with the imminent entry of the United States into the Second Gerra, he decided to join the Bell laboratories, since they collaborated closely in the war effort, it was a sure way to avoid being called up.

Juegos de guerra

Shannon's first job for Bell Labs was to collaborate on the design of fire control systems. His task was to develop the mathematical formulas that would allow calculating the future position of an enemy projectile or aircraft from the information collected by the radar.r from current position. These formulas would then be programmed into primitive computers charged with automatically firing at targets.

When the system was deployed in 1944, it managed to stop 70% of the German bombs dropped against Great Britain.

However, what really interested Shannon was cryptography, so he joined the Bell Labs teams that dealt with ways to keep communications secure.
. His work on the subject was summarized in a 114-page document that was immediately classified as secret by government authorities.

One of the most relevant points of this work is its discovery that the English language is full of redundancy and predictability. In cryptography, the less redundancy a message has, the more difficult it will be to decrypt. Shannon demonstrated that it was possible to reduce redundancy and predictability by removing letters or words without making the message meaningless. There are several psychological experiments that demonstrate how the brain automatically completes sentences by making us see words that are not written.

The three words that make up Claude Shannon's legacy appear for the first time in this document: Information theory.

For Shannon to take the next step in his theoretical formulation, it was necessary to wait for the Bell laboratories to develop a technology based on a theory formulated elsewhere: the so-called pulse code modulation (PCM).

Telephone signals moved from electrical waves. Bell engineers took 8000 samples per second of the rise and fall of these waves and found a way to translate them into zeros and ones or on and off states.
(Remember the two variables in Boolean algebra?) Now, instead of sending waves along the phone channels, you could send information that describes the numerical coordinates of the waves.

In the next article I talk about how this influenced Shannon's work

The prehistory of Unix
Related article:
The prehistory of Unix and the role of Bell Labs
Bringing scientists and engineers together
Related article:
Bringing scientists and engineers together. The prehistory of Unix. Part 2
Vacuum tubes
Related article:
Vacuum tubes. The prehistory of Unix part 3
The arrival of the transistor
Related article:
The arrival of the transistor. The Prehistory of Unix Part Four
Related article:
Mr. Claude Shannon. The Prehistory of Unix Part Five

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  1.   Mr milindri said

    I want to read the second part now.