1. How are computers made?
We started by showing the stuff that computers are made of. It all begins with common sand,which consists mostly of silicon dioxide (quartz). Using chemical methods, the sand is converted to pure silicon. Very pure silicon, 99.999 999% -- you can’t get anything more pure.Pure silicon is a funny material. It shines like a metal, but is breakable like a ceramic. It is a semiconductor. That means it is on the edge: does it conduct electricity or doesn’t it? Well, we can make it do both: make it conduct, or make it stop conducting.We can switch an electrical current in silicon on or off, at will, and very, very fast. From silicon, we make fast switches!
A whole bunch of those switches together make a chip, which is put inside a plastic cover.
A bunch of chips are mounted on a printed circuit board.
A bunch of boards make an electronic box: a VCR, a TV, a radio, a computer.
Well, of course you need more stuff, like a power supply, a display, a hard drive, and a box to fit it all in. But the heart of anything electronic is those silicon switches.
2. What do computers do?
We use computers for a lot of things. Playing games, writing book reports, calculating math problems... It actually all started with math problems. Ÿ So these boxes can calculate quite well. Very well. Ÿ We do know that they do what they are told. You push a button, and the computer does it.It does exactly what you tell it to do (which is not necessarily what you meant it to do...).It follows instructions.
Computers move information, for example your book report from the disk to the printer.Or a file from the Internet to your display screen, or to your own hard disk. They store
information (all the book reports you have written are stored on the hard disk), and they manage it (you can find it again).
How do those silicon switches we talked about actually make all this happen?
This class is going to explore just that: how we can do cool things, such as writing text, making pictures and calculating with switches. Just like computers do.This is called switch logic, or Boolean logic, after George Boole (English mathematician, 1815-1864), who was the first to think of it -- long before electronics existed!
3. Switch logic: OR and AND
The following diagrams are the first circuits we explore: an OR circuit and an AND circuit.While the diagrams are drawn as if these are electrical circuits (a light goes on if the correct
switches are closed), we actually demonstrated these with a water circuit, consisting of a reservoir on top, a catch basin at the bottom, tubes instead of wires, and valves for switches.
George Boole’s switch logic works for water just as it does for electricity!
For the diagrams below, imagine a teacher asking a question. If they think the answer is “Yes”,then the students press a switch on their desk.In the OR circuit, if either Annie or Bert say “Yes” (press their switch) then the light goes on.
(It also works if they both press their switch).In the AND circuit, both Annie and Bert have to agree that the answer is YES, and both have to press their switches for the light to go on.
