The Vacuum Tube is a Very Fast Switch

If you can turn "on" and "off" then you can count... that is the essence of modern binary computers. So, the faster you can make the switch, the faster the computer will be able to run. There are three important versions of this idea, each one faster than the previous. They are: the relay, the vacuum tube, and the transistor.

Electromagnetic relays have been around since the 1800's. When a current is applied to the relay, it creates a magnetic force that pulls a metal contact between two conductors.

The Vacuum tube was invented around 1920(?) and was much faster than the relay because it had no moving parts. The flow of electricity is controlled like a valve controls the flow of water.

Bell Labs invented the transistor in 1954. Like the tube, it has no moving parts. But, instead of being made of glass and wire and plastic, the transistor is made of silicon (like sand) mixed with a few impurities. This construction made it possible to make transistors very, very small. Modern computer chips pack millions of transistors into a single chip!

But, in 1946, the fastest way to switch electricity was with a vacuum tube. So, the scientists at Penn proposed to the Army that they be granted money to build a new machine out of vacuum tubes. This new device would be very fast, and would be able to perform the calculations for the firing tables much faster than the Differential Analyzer or hand calculators.

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