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 truth.

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 understand principle.

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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But How Do It Know? - The Basic Principles of Computers for Everyone.
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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

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 capabilities.

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 speed is.

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 extremely fast.

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.
Below are the first three
chapters of the book.