In general, computers can be classified as either “analog computers” or “digital computers”. Nearly every device that we would today consider to be a computer is, in fact, a “digital” computer. Digital computers are fundamentally based on the concept of a switch. In our computer based course, “Introduction to Computers”, we call it the “Mighty Switch”, because everything about digital computing is based on it. In this article, I want to give you some insights on this concept, so you can help your child learn it.

The idea of a switch is simple, but powerful. Consider an ordinary wall light switch. It has two positions. When the switch is down, the light is OFF. When the switch is up, the light is ON. Simple. Yet on this concept are based the computers that control airplanes in flight, process millions of financial transactions everyday, control heart pacemakers, and let me write this article using a word processor.

For our purposes, we will define a switch as a device that can be in one and only one of two possible states. The two states of the light switch are ON and OFF. It must be in either the ON state or the OFF state, for in our definition there is no in-between and it cannot be both ON and OFF at the same time.

If your student has trouble with this concept, you can also demonstrate it with a coin. You can show them the coin and say “A coin has two states, either HEAD or TAIL.” Flip the coin and let it land. You can observe that “The coin always lands HEAD up or TAIL up. It can’t be HEAD and TAIL at the same time, and there is no in between state.”

But why is this so important? The answer to that question begins in 1847. In that year, an English mathematician named George Boole published a work called "Mathematical Analysis of Logic". In it, he described a new type of mathematics that expressed logic in the form of algebraic symbols. This mathematics has come to be called Boolean algebra. It is concerned with items that can be in one, and only one, of two different possible states. What does that remind you of? The mighty switch, which is always in one state, either OFF or ON.

Boole's new mathematics provided a powerful theoretical basis for computer science. But it wasn't until 1938 that the American Claude Shannon showed that Boolean algebra could be used to describe electrical switching circuits. From that point on, progress was rapid.

In 1941, the German engineer Konrad Zuse (1910 - 1995) built a computer he named the Z3, which is considered by many to be the first ever working programmable computer. This machine used mechanical relays as switches to implement the binary logic that Boole and Shannon had described.

In 1945, another American team, at the University of Pennsylvania, completed the first fully electronic digital computer, which they called the Electronic Numeric Integrator and Calculator or ENIAC. This machine used vacuum tubes as switches, instead of relays, and consequently it could execute Boolean logic much faster than its predecessors.

In 1947, three scientists working at Bell Laboratories built the first transistor, another electronic device that switches between two states. This device was smaller and used less electrical power than an equivalent vacuum tube. It could also switch between states (ON or OFF) faster than a vacuum tube, which made it great for executing Boolean logic, and so computers were soon built using transistors.

In the 1950s, researchers at various companies learned how to build "Integrated Circuits", i.e., "chips". These early semiconductor devices combined several transistors into one device to perform a specific function. Over time, IC designers develop methods for making transistors smaller and faster. Today's integrated circuits contain millions of transistors and can switch between ON and OFF billions of times per second.

Literally billions of integrated circuits are manufactured each year.
They are inside every new computer, car, television, cell phone, building, and so on.
Each one functions according to Boolean logic, and the key to Boolean logic is the switch.
That is why we call it the “Mighty Switch”, and stress that an understanding of this concept
is fundamental to learning about computers.

The “Mighty Switch” and Boolean logic are two topics taught in

“Introduction to Computers – Middle School”,

a 9 week computer-based course from
**StrongTower Software **.

Copyright © 2005 by StrongTower Software Inc. All Rights Reserved.