The title of this book is the punch line of an old joke that goes like this:
Joe is a very nice fellow, but has always been a little slow. He goes into a store where a salesman is standing on
a soapbox in front of a group of people. The salesman is pitching the miracle new invention, the Thermos bottle.
He is saying, "It keeps hot food hot, and cold food cold...." Joe thinks about this a minute, amazed by this new
invention that is able to make a decision about which of two different things it is supposed to do depending on
what kind of food you put in it. He can’t contain his curiosity, he is jumping up and down, waving his arm in the air,
saying “but, but, but, but…” Finally he blurts out his burning question "But how do it know?"
You may or may not have laughed at the joke, but the point is that Joe looked at what this Thermos bottle could
do, and decided that it must be capable of sensing something about its contents, and then performing a heating
or cooling operation accordingly. He thought it must contain a heater and a refrigerator. He had no idea of the
much simpler principle on which it actually operates, which is that heat always attempts to move from a hotter
area to a cooler area, and all the Thermos does is to slow down this movement. With cold contents, the outside
heat is slowed on its way in, and with hot contents, the heat is slowed on its way out. The bottle doesn't have to
"know" in order to fulfill its mission, and doesn't heat or cool anything. And eventually, the contents, hot or cold,
do end up at room temperature. But Joe's concept of how the bottle worked was far more complicated than the
So the reason for the book title, is that when it comes to computers, people look at them, see what they can do,
and imagine all sorts of things that must be in these machines. Or they imagine all sorts of principles that they
must be based on, and therefore what they may be capable of. People may assign human qualities to the
machine. And more than a few find themselves in situations where they feel that they are embarrassing
themselves, like our friend in the joke, Joe.
But computers are actually quite easy to understand. Of course computers have a greater number of parts than
a Thermos bottle, but each part is extremely simple, and they all operate on a very simple, very easy to
With the Thermos, the principle is that of the motion of heat. This is something we can observe in life. We see ice
cubes melting when they are removed from the freezer, and we see the hot meal cooling off on the table when
the family is late for dinner.
In the computer, the principle on which it operates has to do with electricity, but that doesn't mean that it is hard
to understand. If you have observed the fact that when you turn on a light switch, a light bulb lights up, and when
you turn the switch off, the light goes dark, then you have observed the principle on which computers operate.
That is about all you need to know about electricity to understand computers.
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This book is not primarily intended to be a textbook. There are no problems to do at the end of each chapter. Its
intention is simply to demystify the subject of computers for anyone who has ever wondered what’s going on
inside of that box. Of course, it also makes a perfect introduction to computers for a young person who will
ultimately go on to get a PhD in Computer Science. But it should be easily understandable by housewives, senior
citizens and children who can read well. It should be understandable to plumbers and street sweepers. It requires
no previous technical education. It only requires that you can read the language, you can turn a light bulb on and
off, and you can do very simple addition on the order of 8+5=13.
This book presents the complete essentials that make up a computer. It presents every piece and part, in the
proper order so that each one will make sense, and can be understood. Every part is explained fully, and every
new word is defined thoroughly when it is first used. Any attempt to simplify the subject further would leave gaps in
the big picture where someone would still have to guess how the parts work together, and you just wouldn’t ever
have that “Aha, I get it!” moment that I think you’ll soon have.
This book is not a ‘dumbed-down’ version of some college textbook. It is a complete explanation of the basic
principles of computers. It is a technical book, but so is a cookbook and so is a driver’s education handbook. This
book just starts at the beginning and defines every item needed to understand the machine. No matter what
someone already knows about computers, this will fill in any missing pieces and put them all together into
something that makes sense.
Even our friend, Joe, could understand this book with diligent study. There are thousands of words and ideas
associated with the field of computers that make the whole subject seem like a mess. But the basic concepts
underlying them are simple.
In this book, there will not be volumes of trivia about the construction or history of computers, just the essentials,
no more and no less. Each part of the computer has a simple function, and when they are connected together,
you end up with a useful machine called a computer.
There is nothing to memorize in this book. Each chapter is designed to give you a new idea that you didn’t have
before, or if it is something that you had heard about previously, it always seemed confusing. Each idea is very
simple, and one thing leads to the next. Each chapter presents an idea. Each idea is simple and easy to
understand. Later chapters present ideas that build on the ideas from previous chapters.
If someone were to write a book about how to build a house, there could be various levels of detail. The simplest
book would say, “lay a foundation, put up the walls, cover with a roof, put in plumbing and electrical, and you’re
done.” That would not be enough detail for someone who didn’t already have some experience using a hammer
and saw and installing a faucet and wiring a light switch.
At the other end of the spectrum would be a book that had separate chapters for every possible type of
foundation, the different kinds of dirt you might have to dig in, formulas for a dozen different kinds concrete,
charts of weather conditions that are optimum for laying foundations, etc. That would be far too much information.
There would be so many details, that what was really important would get lost.
This book attempts to give just enough detail to see what every computer has in common and how they work, not
how to build the biggest or best computer ever made. It is not about any specific brand of computer. It is not about
how to use a computer. If it were a book about building a house, it would probably describe a simple plan for a
sturdy garden shed with a sink and one bare light bulb, showing the size and shape of every piece of wood, where
to put all the nails, how to hang the door and how to put the water pipes together so they wouldn’t leak. It would
not show how to build anything as complicated as a fancy curved oak staircase.
We are going to show the one simple part that computers are made of, and then connect a bunch of them
together until we have built a complete computer. It is going to be a lot simpler than you ever imagined.
Just the Facts Ma’am
Computers seem mysterious and magical. How can they do what they do? They play games, they draw pictures,
they 'know' your credit rating. These machines are capable of doing all sorts of strange and wondrous things. Yet
they are simple. They can do only a very few, very simple things. And, they can only do one of these simple things
at a time. They appear to be doing complex things, only because they do a huge number of simple things one
after another in a small amount of time. The result, as in a video game, is very complex in appearance, but in
reality, is very simple, just very very fast.
Computers are designed to do a small number of specific simple things, and to do these things quickly, one after
the other. Which simple things are done, and in what order, determines what sort of task the computer
accomplishes in any given time, but anything the computer does consists of nothing outside of its limited
Once you see what a computer is made up of, you will come to realize how it is that they can do what they do,
exactly what sorts of things they are capable of, and also, what they are not capable of.
So the secret of computers is not that they are complex, rather it is their speed. Let’s look at exactly how fast their
Since computers work on electricity, their speed is related to the speed of electricity. You may remember hearing
that the speed of light is 186,000 miles per second. That’s pretty darned fast. Light can go around the entire
earth seven times in one second, or from the Earth to the Moon in about a second and a half. Per the physicists,
electricity has many properties in common with light, and its speed, when traveling in a wire, gets slowed down to
about half the speed of light. But still, going all the way around the Earth three and a half times in one second is
As a point of comparison, imagine it is a hot day and you have an electric fan sitting on the table blowing cool air
on you. The fan is spinning around so fast that the blades are a blur, but it is only spinning around about 40 times
each second. A point on the edge of one of those blades will only travel about 150 feet in that second, it will take
35 seconds for that point to travel just one mile.
Since the fan blades are already a blur, it may be hard to imagine them going just ten times faster. If it did, that
fan would be putting out quite a breeze. And if you could make it go a hundred times faster, it would almost
certainly self-destruct, with fan blades breaking off and getting stuck in the ceiling. But electricity traveling in the
same circle would go around about a hundred million times in one second, that’s two and a half million times faster
than the fan blades. That’s fast.
A million is a very large number. If you took a big sheet of paper that was 40 inches square and took a ruler and
placed it at the top edge, and drew 25 dots per inch along the top edge of the paper, you would have to draw one
thousand dots to get across that sheet of paper. If you then moved the ruler down the page 1/25th of an inch, and
drew another thousand dots, and kept doing that, you would have to move the ruler down the page one thousand
times, each time drawing one thousand dots. If you could complete such a boring task, you would end up with a
piece of paper with a million dots on it. That’s a lot of dots or a lot of anything. And just to finish the thought, if you
could find a thousand people who would each draw one of these million dot sheets, and stacked up those
thousand sheets in a pile, you would then have a billion dots.
Now let’s say that the electricity moving around inside the computer can accomplish some simple task by traveling
one foot. That means that the computer could do 500 million simple things in one second. Again for comparison,
the fan on the table will spin for 7 hours to go around just one million times and it will take a full six months for it to
spin around 500 million times.
When you talk about the speed that electricity can move between parts inside the computer, some of the parts
you can see are a foot apart, some are closer, an inch, a tenth of an inch. And inside these parts are a multitude
more parts that are very close to each other, some just thousandths of an inch apart. And the shorter the
distance the electricity has to travel, the sooner it gets there.
There is no point in saying how many things today’s computers do in a single second, because that would date
this book. Computer manufacturers continue to produce new computers that go twice as fast as the fastest
computers of only two or three years past. There is a theoretical limit to how fast they can go, but engineers keep
finding practical ways to get around the theories and make machines that go faster and faster.
During all of this time that computers have been getting faster, smaller and cheaper, the things that computers
do, really have not changed since they were first invented in the 1940's. They still do the same few simple things,
just faster, cheaper, more reliably and in a smaller package.
There are only a few sections to a computer, and they are all made out of the same kinds of parts. Each section
has a specific mission, and the combination of these parts into a machine was a truly marvelous invention. But it is
not difficult to understand.
the first three
of the book.