What's a computer?

My wife once told me about her first lecture in Computer Science back in her college days. The teacher walked in and started talking about history of computers, data, files, computer languages and “lots of other hyperbole”. She didn’t understand anything out of the one hour lecture. Soon after that, she switched to Political Science.

I have heard similar stories of people getting a rough introduction to computers. That got me thinking about how I got introduced to computers. I remember in my very first class (I was 12 then), my teacher Mr. Jhulan Chakraborty started by explaining what a computer is. What he said, stayed with me ever since:

A computer is a machine – just like a ceiling fan, a sewing machine, or an engine in a car. But, it’s a different kind of machine because of two important properties:

1. You can provide a step by step instructions to it and it will follow the instructions exactly to the letter – without any error. Just as you provide instructions to your housemaid for a task. However, unlike a human—
2. A computer while following the instructions, can do repetitive tasks, without getting bored, without any error, and with substantial speed.

That’s it. That is all a computer is.

I think, that is a brilliant introduction. It is concise and accurate. It also serves as a baseline for introduction of more advanced topics. For example, programming languages are just a language for specifying the instructions to a computer (see step 1 above).