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		Yes Dorothy There Is a Computer
				or
		What You Should Know about Computing

It has been my good fortune to have been associated with the development
of the modern Digital Computer for many years.  During this period I have
been asked on numerous occasions to explain the computer to people who
were not scientists.  With the wide spread use of computers in business,
the general public has become aware of computers and of the many things
that they do, but, strangely enough, I have found it to be inceasingly
difficult to get people to understand what computers are all about.
Somehow or other, many people have formed the idea that computers make use
of some sort of magic that is beyond their comprehension and they tend to
simply shut their ears.  Please, I beg of you, do not do this tonight.

Let me assure you that you WILL be able to understand most of what I am
going to say.  Computers do not work by magic, they make use of some very
simple principles that are really quite old.  Of course, the modern
digital computer is a very ingenious electronic device but the basic ideas
back of its design are really very simple and are easy to understand.

Will it help, if I tell you that the basic principles of the digital
computer were first suggested by an Englishman Charles Babbage in 1833,
yes, 1833 not 1933.  Furthermore, the first really clear explanation of
these ideas in English was written by a 28 year old woman, Lady Lovelace
the daughter of Lord Byron, the English poet, in 1844.  If Lady Lovelace
could understand the principles of the computer, surely you should be able
to do this today.

One of the impediments to understanding has been the development of a
special computer jargon which has grown up and in which some simple
non-human devices are given names that imply human characteristics.  If I
should start using some of these terms or saying things that you do not
understand, I want you to interrupt me then and there.  This is not going
to be a set speech but rather an attempt to get you all to understand
something about computers.  I welcome interuptions and questions.

Of course, I do not expect you to understand the inner workings of a
computer, just as most of may not understand all about the inner workings
of many devices that you use every day.  How many of you understand the
inner workings of your automobile or perhaps an even simplier device such
as the lock on your door which you use every day without any feeling of
mysticism?  In the same way that you understand how a lock works, that is
how to lock your door and to use your key to open it, you should
understand how a computer works.  Actually you should understand a bit
more than this just as you understand that just any key will not open your
door but that the key must have bumps and hollows on it that exactly match
some parts inside of the lock in order for the key to work.  That is, you
should have a functional understanding.  You should understand what the
computer can and can not do without bothering about how it does these
things in detail.

You must first put out of your mind any idea that the computer is some
sort of magical device that can do all sorts of mystifying things.  The
computer is simply a glorified adding machine that has three rather
special features added.  Oh, of course, some very special engineering has
gone into the design and construction of the modern computer which I do
not expect you to understand or indeed be interested in understanding but
you should and can understand what the computer can and can not do.

The computer gains it power from the fact that it does quite simple things
very fast and from the fact that it practically never makes a mistake.

First to give you some idea of its speed.  Suppose you were asked to add
two ten digit numbers togather, say add 8,370,625,784 to 1,987,476,647.  I
tried this myself and it took me 12 seconds after I had written the
numbers down which took 10 seconds.  Now if these numbers are stored in
the computer and it is told to add then the entire operation will take
less than one millionth of this time, In other words the computer can make
one million additions of this sort while I am making one.  There are even
faster computers than this but the figure of one million is not too far
wrong for most computers used today and it is an easy number to remember.

Now as to its accuracy.  Computers seldom make mistakes.  When I say
seldom I am of course refering to seldom in relation to the number of
operations that it performs.  If a computer makes one mistake a day, and
this number is high for a well maintained computer doing routine work, it
still will have preformed well over ten thousand million correct
operations before it makes a single mistake.  Compare this with your own
rate of error when you try to add a string of numbers.

But even when computers do make mistakes there are two factors that
prevent this mistake from going undetected.  In the first place most
computer errors are apt to be of a type that will cause the computer to
stop working completely so that the human operators are alerted to the
trouble and steps can be taken to verify the operations that were underway
when the failure occured.  Then, almost always the set of instructions to
the computer will call for some consistancy checks, double entry
bookkeeping checks and the like.  These checks will detect those few
errors that would have otherwise have gone undetected.

Those of you who have had troubles with computer rendered bills may
dispute this last statement but take my word for it, substantially all the
mistakes that are blamed on the computer are not the computers fault at
all but are caused by human errors in typing information into the
computer.  Sometimes the mistakes are in the set of instructions to the
computer but these instructions are used over and over again, in the case
of billing for every customer and so these kinds of mistakes are usually
found right away and get corrected.  Of course, your account may be the
very first account that was processed after a bad set of instructions had
been give to the computer.  More often than not the trouble will have been
caused by a typist who simply typed in incorrect information to the
computer about your account.  Typing information into a computer can be a
very monotonous operation and typists can and do make mistakes.

But to get back to the special features that make the computer something
more than an adding machine.  When you use an adding machine to help you
balance your accownts you must punch in numbers as you come to them and
then hit the right key to tell it to add or subtract or multiply.  When
you use a computer some of the numbers will had already been stored in the
computer and usually the complete set of instructions that are to be
followed will also have been stored and you will only have to give the
computer a single starting instruction and it will exicute the previously
stored instructions one after the other.

We explain this ability of the computer to store information by saying
that the computer has a MEMORY.  Now this memory is not a memory like the
memory that a person has, not at all.  It is really only a storage device
in which instructions, letters and numbers can be held.  Charles Babbage
called this part of his machine the STORE which is a much better term than
MEMORY.  Perhaps if you think of this memory as simply a piece of paper on
which instructions and numbers can be written, you will not go far wrong.

Actually there are be several different parts of the computer that may be
used to store information.  You can think of these as being different
pieces of paper.  One of these may be used to store the instructions that
are to be used over and over again and that are to be protected against
accidental erasure and that can only be read.  Another piece of paper may
be used as a Day book on which new entries can be made but on which old
entries are never changed. Still another piece may be use as a scratch pad
for temporary calculations, etc.

The set of instructions to the computer is called a computer program.  The
actual instructions that the computer can execute are all relatively
simple and the complexity of the things that the computer can do is
determined by the fact that the program can contain a very large number of
individual instructions.

People who write these sets of instructions are called programmers.  You
can gain some idea of the problems that these people face if you think of
the computer as a very fast and accurate moron who can read and write and
knows how to do arithmetic but knows absolutely nothing about the real
world. The programmer must write a set of instructions for this moron
telling him how to keep all of the records and do all of the bookkeeping
for a large bank or a large chain of stores.  I will have more to say
about this later.

The next part of the computer is a simple control device that can read the
instructions that are in its memory, I mean that are written on its
internal piece of paper, and can call on the adding machine to execute
these instructions, one after the other.  Many of these instructions will
be to add two numbers togather or maybe to add a whole string of numbers
togather and to store the sum again on its internal piece of paper. Others
will be to subtract one number from another and some will be to multiply
or devide other numbers.  By this means a fairly involved computation may
be carried out.  These numbers could well be numbers relating to the
deposits that have been made to your checking account and the checks that
you have written so that the computer could be computing your current
balance. Other instructions will call for letters and numbers to be moved
or copied from one part of the internal piece of place on the internal
piece of paper to another so that desirable information can be put
togather and so that bills and statements can be prepared.

The important differencee between the computer and the simple adding
machine is that the instructions can be all stored in advance and they can
be executed one after another without further human intervention.

There must, of course, be some devices that allow a person or several
people to store the instructions αnd numbers into the computer, thers are
usually typewriter like keyboards.  And then there must be an output
device, called a printer to prepare output documents for human use,
perhaps a monthly bank statement. These devices are called INPUT and
OUTPUT devices.

So far there does not seem to be anything that is not easily understood.
Oh, I do not mean that you now understand how in detail the instructions
get written on this internal piece of paper when one hits a key on an
input device, but then do you understand how your electric typewriter
works in detail but I am sure that this does not prevent you from using it
and you do not expect it to do magical things.

Let me repeat, we now understand that a computer consists of four distinct
parts, 1) an internal store or piece of paper, mistakenly called the
memory, 2) an arithmetic device that can add, subtract, devide and
multiply, 3) some input and output devices that allow people to put
instructions and numbers into the internal piece of paper, and 4) a
control device that causes instructions to be executed one after another.

I have conviently neglected to tell you one or two details about the
functioning of the computer, which we will now have to understand.  But
remember that you now know fully 90 percent of what you need to know to
understand the modern digital computer.  This one bit of missing
information is the bit that Charles Babbage and Lady Lovelace supplied in
the early eighteen hundreds.

Prior to Babbage several people had built machines that could follow a set
of instructions that could be stored in advance.  I will only mention one,
this being the Jaquard Loom. This loom used a set of punched cards to
control the lifting of the treads of the warp so that a complecated
pattern could be woven into a cloth.  For repetive patterns these cards
were used over and over again but some 24,000 cards were used on one
occasion to produce a cloth portrait of M. Jacquad himself.

To understand what is missing in all of this let us assume that you have
written a set of computer instructions for a bank.  When a deposit is
made, the amount of the deposit is to be added to your balance and when a
check is received the amount of the check is to be subtracted. Every thing
goes along nicely until you write a check that is larger than the then
remaining balance in your account.  Wnfortunately, the bank may not want
to honor such a check.  You might skip town and leave them holding the
bag.

So how do you handle this situation?  Well, it is really very simple.
There must be an instruction that causes two numbers to be compared and
that will interupt the orderly executing of a string of instructions if
one of these numbers, in this case the size of the check is larger than
the other.  There must be a second string of instructions which are to be
followed in this case and which will cause the check to be returned
uncashed.  You can easily see that there will be many situations where the
comparison of two numbers will have to be used to decide where in a
complecated set of instructions the next instruction is to be obtained.

You can thing of this as being done by an old fashioned balance with two
balonce pans. Sugar is put into one pan in an amount corresponding to one
number and into the other pan in an amount corresponding to the other
number.  When the balance tips one way or the other the next instruction
is taken from the list under the lower pan.  There may even be a third
list of instructions that are to be followed if the beam stays in balance.

Computer people sometimes say that the computer decides what to do next
on the basis of a comparison of two numbers.  One could with equal juatice
say that a scale decides to tip one way or the other on the basis of the weights
in its two pans.  This is just another example where jargon confuses one
and makes the uninitiated think that some magic is involved.

It is this ability to have many different lists of instructions and to
switch from one list to another on the basis of the comparison of two
numbers that constitutes the idea that Babbage and Lady Lovelace first
described in the early 1830's and that constituted the basic invention of
the digital computer.

Babbage was never able to complete his Analytic Engine, not because he did not
understand how to do this but simply because he had to depend entirely on mechanical
devices. The mechanical technology of the times was quite unable to cope
with the demands for precision that his machine demanded.  For that matter we
would be hard pressed even today to complete the Analytic Engine using mechanical
devices only.  Over one humdred years were to elapse before
technology was advanced enought for these basic ideas to be implemented and
it took the computational demands of the second
world war to provide the impetus for this computer to be developed.

A little modern history may help to put these matters into perspective.  I
first became interested in machines to do mechanical computations in 1923 when
as a student at MIT I worked on the Bush Differential Analysiser.  This was
what we call today an analogue computer.  Strangely enough, Babbage's ideas
had been largely forgotten.  People who did learn of this work also learned that
it had been unsuccessful and they failed to note that technology had inproved
to the point that what had been impossible was, in fact, now possible.

During the 1930's and the 1940's a few people started to work on digital
computers but strangely enough these early computers were largely concerned
with what I might call straight-line computationsm that is they did not have
the ability to compare one number with another and to go to different sets of
instructions on the basis of this comparison.  During this period I had gone
on to other things but because of my earlier interests I kept cposely in touch
with the computer work and was personally acquainted with all of the workers
in this field.
 
When the second world war came along, the computational demands far
exceeded the capacity of the then existing machines and various people,
principally at Harvard University, IBM, the Bell Telephone Laboratories
and The University of Pennsylvania started active work on strictly digital
computers.  Most of this work was shroudded in secrecy and it was directed
toward military ends.  The Harvard, IBM and Bell Laboratories work was
largely directed toward the use of relays while the work at the University
of Pennsylvania was on an entirely electronic computer.  Some idea of the
complexity of these early machines can be gained from the fact that the
Machine at the University of Pensylvania contained 18,000 vacuum tubes.

When knowledge of this work became generally known at the end of the war
there was a flurry of activity.  The University of Pensylvania's group
split up, Mauchly and Eckert left to form their own company, John Von
Neumann and some of his close associates went to the Institute of Advanced
Study at Princeton.  MIT got into the act in a big way, and many other
groups were formed both in this country and abroad.

With all of  this activity,  computers were slow  to come  on the  market.
There were  several reasons  for this.   The requirements  that  computers
placed upon their component parts was extremely severe.  Some idea of this
problem may be gained considering the problem of vacuum tube  replacement
in a machine using  18,000 vacuum tubes when the tube manufacturers did not
expect their tubes to last more than about 1000 hours.  This meant that some 18 times  an
hour the machine  would stop functioning  and it could  not be started  up
again until tthe failed vacuum tube had been located and replaced.
The wonder is that people had the audacity to try to build such device, but
they did.

Some idea of the slowness in getting computers on the market can be gained
from the fact That I happened to move from the Bell Telephone Laboratories
where we were moderately well equipped with computational aids to the
University of Illinois where such things were still ubnheard of.  As
strictly a user at the time I was involved in trying to buy a computer.
Failing in this we started to build our own which was later to be known as
the Illiac.

Having gotten back into computers, by the back door, as it were.  I switched
my allegance from vacuum tubes and Radar to computing.  By 1949 I decided that
I would have to get back into industry if I wanted to see much action in this
field and I joined IBM.  As of 1949 IBM had suddenly awakened to the fact that
they were way behing in the electronic digital field and that they would have
to do something about this. By 1952 they had a new computer the 701 ready for the
market and they were off to a good start.

If we had time, I could go all the way back to the ancients and tell of
the early attempts to make adding machines but I will start with Charles
Babbage.  Charles Babbage was a mathmetician who lived in England during
the early 19th century.  He was a very queer man indeed and made enemies
of nearly every one but he was a very clever man.  And lest you thing that
I am going to talk about men's doings exclusively let me hasten to mention
Lady Lovelace who also played a prominent part in the early development of
computers.  Charles Babbage first came to wide public attention when he
proposed a special device which he called a Difference Engine.  The
device, on which he devoted years of his life was a special adding
machine-like device that was to help in the compution of astrnomical
tables that are used in navigation. This was to be an entirely mechanical
device, since this was much before the days of electronics.

Babbage was beset with difficulties.  There were no such things as
standard machine parts in those days.  If one wanted a simple machine
screw one had to make it. The nut to fit the screw had to be made
specially for it.  Parts, being more or less hand made , were never
interchangable.  In addition Babbage was forever changing his mind.  Now
sooner had he started to build one machine than he got an idea for a
bigger and better machine and he would start all over.

In 1833 while temporarily held up for lack of funds, Babbage conceived of
a machine which he called an Analytic Engine.  This was to be in all
essentials a digital computer, as we know it today. not an electronic
device of course, but a mechanical one.  This machine was to consist of
four major parts as I have just described.

Babbage was verypoor at explaining his ideas.  He wrote many books and
papers but they were almost impossible to read and understand.  And here
it was that Lady Lovelace entered the scene.  Lady Lovelace was the only
legitimate daughter of no less a person than Lord Byron the English poet.
Her husband was interested in horse racing and somehow he got the idea
that Babbages new maching could be used to analyse racing results so that
he could bet only on winning horses.  It is not at all clear that he quite
understood what Babbage's machine would be able to do but Lady Lovelace
certainly did understand.

In those days it was quite unbecoming for a woman and a titled Lady at
that to interest herself in mechanical devices and so Lady Lovelace masked
her interest.  It happened that Babbage was invited to deliver a lecture
in Italy and one of Garabaldi's generals wrote a paper in Italian
describing this lecture.  Lady Lovelace, thereupon undertook the task of
translating this Itallian paper into English, since Translating was a
lady-like pursuit.  She thoughtfully appended copious notes to this
translation.  In fact the notes were more extensive than was the paper
itself, and these notes remain to this day, the clearest exposition of
Babbages ideas that exist.  In fact there are some people who feel that
some of the ideas attributed to Babbage werre in fact Lady Lovelace's
ideas.

Incidentally Babbage never did get his machine to work, Lord Lovelace lost
most of his fortune playing the races and even had to pawn the family
jewels to meet his gambling debts.

But what is this additional idea that makes the computer so powerful?  In
the simplest terms this is the ability to compare two numbers in order to
see which is the larger and to go to different places in the list of
instructions on the basis of this comparison.  Let us see how this might
work.

Consider the case where a teller at the bank is ready to debit your
account for a check that has just come in. The teller puts your check into
a machine which can read the funny numbers that appear on the check to
identify your account number.  This starts a computer program. This
program is one that some one had to write in complete detail and which is
stored in the machine as a list of instructions on this internal piece of
paper that we have talked about.

The first instruction causes the computer to read your account number from
the check.  The computer must then locate information in its store that
relates to your account and in particular what your current balance
happens to be. Some where in its store there will be a list of all the
currently valid account number, which we will assume are listed in serial
order.  The next instruction will set a pointer to the first number on
this list.  Then there will be an instruction specifying that the account
number from your check be compared with this number. If these numbers
agree then your account has been found.  This will cause the next
instruction to be taken from a separate list of instructions which
slpecifies what is to be done in this case.  If the two numbers do not
agree then either your account number is larger than the one being pointer
to or it is smaller.  If it is larger then presumable your account number
will appear somewhere further down in the list so the next instruction in
this cace should cause the pointer to be moved down one on the list and
the control switched back to the earlier instruction that called for a
comparison to be made.  In this way a small set of instructions are used
over and over again in locating your account.  Indeed this same set of
instructions are used for every check that is processed.  You can see why
I said that simple errors in the list of instructions will be quickly
found.  We have not discussed what happen the comparison shows that the
number on your check is smaller than the number with which it is being
compared.  Well in this case your check cannot be honored and the program
control is switched to a set of instructions that are to be followed in
this case.  Actually there are many more instructions than those I hav
described, all connected with identifying the account that is to be
debited.

Having found the proper account then other tests must be made.  Perhaps
the check is larger than your remaining balance so a comparison must be
made between the amount of the check and your balance.  If the check is
too large then a check will have to be made to see if you have arranged
for automatic borrowing.  If the check is not too large then other tests
will have to be made.  Perhaps you have stopped payment on this prticular
check or there may be a minimum balance requirement on your account or
maybe you are allowed only aa fixed number of checks each month.

There are tests after tests and all of them require that two numbers be
compared and that a different list of instructions be followed depending
upon the results of each and every such test.  I haven't begun to list all
of the tests that have to be made.  When the complete list of instructions
have been prepared there may be many thousands of instructions all having
to do with debiting the proper account for each check that must be
processed.  So what looked like a fairly simple operation turns out to a
long drawn out series of instructions none of which that are at all hard
to understand.  The writing of these instructions, called programming can
be a very time consuming and difficult process because the programmer must
think of every possible situation that can possibly arrise and he must
prepare the list of instructions telling the computer what to do for every
situation.  Let me remind you however tha the computer is very fast and
thousands of individual instructions can still executed in an extremely
small fraction of a second.


    Secondly I want to dispell two commonly held misconseptions about
computers because the holding of these beliefs acts as a road block to a
clear understanding of the importances of computers and the role that they
are sure to play in the future.

    Thirdly I want to explain how a computer works in very simple terms.

    I want to do just one thing tonight and that is to dispell any
feelings that you all may have that Computers are completely beyound your
understanding.


    There are two quite widely held views of computers that are completely
fallacious.

    In a brief talk such as this, I cannot hope to make you all into
computer specialists.  There is, however, one thing that I can hope to do
and that is to make you all realize that you can in fact understand how
computers are used and what they can and cannot do.

    Computers are neither magical devices that can do anything nor are
they very dumb devices that are always making dumb mistakes. I am sure
that most of you tend to

    Two widely held views of computers are largely responsible for the
fact that most
TITLES

What the layman needs to know about computing.
What the layman should know about computing.
Computer Magic vs Computer Understanding
Debunking Computer Gobbledygook
Computers Made Easy
Facts and Fancies about Computers
Computers are OK but I wouldn't want my daughter to marry one
The How's and Why's of Computers
What can I Understand about Computers
Understanding Computers
Is there a Computer in my Future?
The Computer Revolution
You can understand Computers
If you know how to add you can understand how Computers work
Do computers make mistakes like people do?
Human or Computer Errors
Why must Computers be used?
Are Computers Necessary?
The Uses of Computers
Computer A B C's
A B C D Computer
Computers are Fun
The Computer in Your Future
I don't Understand Computers
Don't Discount the Computer
The Computer made a Mistake, but did it?
Don't Blame the Computer
Once there was a Computer
The Computer Menace
Are Computers a Menace?
Coping with Computers