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			   Computing Made Easy
				    or
		   What You Should Know about Computers

I. Introduction.

In spite of all of the false information about computers that is floating
around, computers are quite easy to understand if one will dispel any
lurking suspicion that the computer possesses some sort of power that enables
it to do mystical things.  Let me assure you that you are going to understand
what I am going to be saying.  Oh of course, the modern digital computer is a
very ingenious and complicated device, but many other things that we use every
day are equally complicated and this does not keep us from feeling quite
comfortable in using them.

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 was written in 1844 by Lady Lovelace, the 28 year old daughter
of Lord Byron, the English poet.  If Lady Lovelace could understand the
principles of the computer in 1844, surely you should be able to do this
today.  Let me show you a picture of this early Victorian lass.

SLIDE 1.

And now let me show you three quotations.  These quotations
present three quite different points of view, each true if read carefully
but each subject to misunderstanding by the unthinking.

SLIDE 2.

    "The Analytical Engine [the Computer] has no pretensions
    whatever to originate anything.  It can do whatever we know
    how to order it to perform."  Lady Lovelace in 1844

This is as true today as when it was written.

    "Apart from the question of its saving labour in operations
    now possible, we think that the existance of an instrument
    of this kind would place within reach much which, if not
    actually impossible, has been too close to the limits of
    human endurance to be practically available."  A committee
    of the British Association in 1872

Also still true.

    "Man has in a single generation found himself sharing
    the world with a strange new species: the computer and
    computer-like machines."  Marvin Minsky in 1967

True if one does not ascribe human characteristics to this new species.
But more on this later.  Let's get a little historical perspective naw.

Charles Babbage is usually credited with the invention of the digital
computer.  However, its origins go back much further, back even to the
dawn of recorded history.

II. Early history

The problem of keeping records is perhaps some of the dullest repetative
work that falls the lot of the so-called white-collar worker in an office.
This has always been so, and it has always lead to the development of
mechanized aids.

In fact, if one goes back far enough, it seems that the invention of
writing itself was prompted by the need to keep accounts.  The oldest
surviving written records, dating from some 5000 years ago, were primitive
books of accounts inscribed on clay tablets by the Sumarians.  Curiously
one of the earliest written records that was not of this type contained a
lament for the "good old days" and a statement that the world was going to
the dogs because children no longer obeyed their parents.

While the Linear A writings of the early Minoans has not yet been
decyphered, all of the surviving records in their Linear B language were
bookkeeping records, and this well before 1470 B.C.

Even in Egypt where most of the records that have survived are on temple
walls and are praises of the Pharohs and of the Gods, the real reason for
the invention of their form of writing is thought to be the need to
preserve survey records of land holdings during the annual flooding of the
Nile.  The preservation of historical and cultural information could well
be left to oral transmission, but when it came to settling disputes
between adjacent land owners, nothing took the place of a written record.

Writing can be looked upon as being a mechanical means of supplementing
and even of replacing man's memory.

Similarly there has been a long history of attempts to make mechanical
devices to supplement and replace man' ability to do arithmetic.

Perhaps the earliest device that has survived to this day is the abacus.
I have one here and perhaps you can see it on the next slide.

SLIDE 3.

The abacus came to us from the orient and was not introduced into Europe
until around 1000 A.D.  Its design is based on the method of representing
numbers known as "positional notation", a notation that was introduce by
the Aribs and that you all know but not by this name.  I am sure you have
all heard of the man who discovered rather late in life that he could
speak in prose.

To understand the importance of a positional notation consider the problem
of multiplying two numbers using Roman notation.  Try, for example, to
multiply MDCXVIII by MDCCCCLII.  By rewriting these numbers in the more
familiar "positional notation" form the problem is greatly simplified,
but multilpication is still a more difficult operation than is simple
addition.

The invention of logarithms by Napier in the 16th century, made it
possible by the use of tables to multiply two numbers by adding their
logarithms.  This was a long step in the simplification of computations.
Unfortunately, the general public has never become conversant  with
logarithms and so this is still within the domain of the scientist and
the engineer.

But to return to mechanical aids.  The abacus is still primarily a memory
device in that it remembers the initial and intermediate states of a
calculation.  To develop any speed in using it must still be able to add
up to 9 plus 9.  Many attempts were made through the centuries to make
mechanical adding machines;  Pascal and Leibnitz, in the 17th century made
notable contributions along these lines but it has only been within the
19th century that the desk calculator came into general use.

An now, I suppose, it is time to point out the differences between a
desk calculator or its more modern form the pocket calculator and the
digital computer.  The most apparent
distinction is one of size and cost but this distinction is becoming blurred as
more and more elaborate calculators come on the market and as computers are
becoming smaller.  Some pocket calculators are, in fact, really simplified
computers, but to clarify your thinking I want to draw a sharp distinction.

When one uses a simple pocket calculator, one enters the numbers into the
calculator as they are to be used and one causes the calculator to perform
one operation, that is one addition, subtraction, multiplication or
division at a time.  If one uses a calculator,for example, to figure one's
income tax, one must keep track of the sequence of operations that are
required and one must enter the needed numbers and depress the needed
operation keys in the proper order if one expects to arrive at the correct
answer.

When one uses a computer, one supplies it with all of the numbers that it
will need ahead of time, and in fact many times the numbers are already
stored in the computers files.  Then one supplied an ordered list of the
operations that one wants done.  This list is called a "program".  Having
done this, the computer is given the signal to start, where-upon the entire
series of operations is done without further human invention.

Just as one must do the required operations in the proper order when using
a desk calculator, so one must have the desired operations specified in
the proper order in the program that one gives to the machine.  There is
one big difference however.  If one writes a program to compute ones
income tax then this same program can be used again and again to compute
the income tax for other people.  The program remains the same and only
the input numbers change.

Now actually computing ones income tax is much more complicated than just
performing a number of additions, subtractions, and multiplications, as 
any of you know who have even looked at the forms.  There are all sorts
of decisions to be made, usually based upon the comparisons of two numbers,
if the value in column 21 is larger than the value in column 34 then
enter the difference in column 46, otherwise enter 0 in this column.

When you use a pocket calculator you must make these comparisons and you
must do the right thing.  When you use a computer, it must make these
comparisons and it must then do the right thing.  So the program is a
good deal more complicated than being simply a list of mathematical
operations that are to be performed.  It must also contain commands
that will cause the computer to make comparisons and to jump to different
places in the list of instructions for its next instruction depending
upon the outcome of these comparisons.

This then is the remaining, and certainly the most inportant, difference
between a calculator and a computer.  I have summarized these differences
between a the calcuator and the computer on the next slide.

SLIDE 4.

And now it is time to get back to our story about Charles Babbage and
Lady Lovelace.

Charles Babbage was a most interesting man.  He was a man who was ahead of
his time and he was most impatient of those who were not as far seeing.
In many cases, his ideas had to wait until better means were at hand to
implement them, but even when this was not the case his intolerance so
antagonized his associates that they put every impediment they could in
his way.

Thus it was with his ideas regarding what he called his Analytical Engine.
I will not burden you with an account of Babbages many inventions.  Suffice
it to say that in 1833, while the construction of an earlier machine was
suspended for a year, Babbage conceived of the basic idea back of the modern
digital computer, and he spent the rest of his life in a vain attempt to
construct such a machine.

After Babbage's death in 1871 a committee of the British Association
examined his engine and made a hrport which contained
the quotation that I showed earlier.
This conclusion is as true today as it was
then and we have the modern equilivent of Babbage's Analytical Engine in
the Computer.

Now let me describe Babbage's Analytical Engine and by analogy the modern
computer in much the same terms that Lady Lovelace used in 1844.

If a machine is to perform the functions of a human computer it must possess
four distinct parts.  These are:

1) An arithmetic unit, capable of performong the normal operations of
arithmetic.  Babbage called this unit the mill.  A pocket calculator has
such a unit.  In the modern computer this is a part of the CPU (central
processing unit).

2) A storage unit, that is a mechanism which will retain numbers and also
the instructions that will be needed.  Babbage called this part of machine
the Store.  In modern computer terminology it is called the Memory.
When a person does a calculation by hand he uses pieces of paper to supplement
his own memory, and by analogy we could call these pieces of paper a memory.

3) A comparison and switching unit, that is a built in ability to compare
two specified numbers (that may have beeen computed) and to take different
courses of action depending upon the result of this comparison, that is to
go to a different place in the list of instructions (the program) for the
next instruction.  People sometimes say that the computer "decides" what
to do next, but this is ascribing human capabilities to the computer.  The
decision was actually made by the person who wrote the program and the
computer is only doing what it was told to do.  This part of the computer
is a comparison and switching device only.

4) Input-output mechanisms which allow the operator to put
numbers and instructions into the machine and to extract the results of the
calculations from the machine.  Babbage proposed to use punched cards as
input, and this was 1833 remember. and proposed to have the maching set
up its results in type where necessary.  We have many different kinds of
input and output devices available today, from typewriter like devices to
machines which automatically read type or magnetically record records.
Your dividend checks are one form of printed output which the modern computer
produces.

Now let me list these four parts of the computer on the next slide.

SLIDE 5.

That's all there is to a computer, just four quite prosaic parts, prosaic
at least in terms of their function, but, of course, they are marvels
of engineering perfection in terms of the way in which they are built.

Now in case this discussion has still failed to disaffirm your belief
in the mystical powers of the computer, let me state catagorically that
the computer can not do anything that a person cannot do with a pencil and
piece of paper.  The computer can only do it faster and with less danger
of making an error.  

Let me return again to the quotation from Lady Lovelace.

SLIDE 6.


Now you know about all you need to know about computers

But why use computers?  Let me explain this by the next slide.

SLIDE 7.

Finally perhaps I should say a few words about ths speed, accuracy and
reliability of the modern computer.

SLIDE 8.




I have made this outline primarily so that I will not forget some parts
of my story, but I would be very happy if you would interrupt and ask
questions.  It is more important for you to understand something about
computers than it is for me to finish a set speech.  This is
an attempt to get you all to understand something about computers.

Of course, I do not expect you to understand the inner workings of a
computer, just as most of you 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.  What we are talking
about is a functional understanding.  You should understand what the
computer can and can not do without bothering about how it does these
things in detail.

It will be necessary to first point out the difference between  a calculator
and a computer.  Actually the distinction is becoming a bit forced as many
of the so-called pocket calculators are gradually taking on some of the
functions of computers. Basicly a calculator will do but a single operation
before manual intervention is required to supply the information
for the next wanted operation, while with a computer one can specify in
advance an entire sequence of operations togather with all of the input
values that will be needed and then the computer is able to carry out
the entire sequence.  I have indicated this and the other significant
differences on the next slide.
SLIDE 3.

The computer can only do a sequence of very simple operations
It gains it power from the fact that it does a long sequence of these simple
things and it does this very speedily with practically no mistakes.

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 them, 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:  A computer seldom makes a mistake.  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 performed 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.

Because of the great speed of the computer, it is reasonable for it to be
asked to perform all sorts of checks on its own operations, error checking
routines, double entry bookkeeping types of checks etc. so that computer
generated mistakes seldom escape detection.  Mistakes blamed on the computer
are almost always human mistakes in supplying the computer with input
information.here is a truthful albiet inelegant expression used by
computer programmers, G.I.G.O. which stands for "garbage in, garbage out".
These aspects of the computer are sumerized on the next slide.
SLIDE 4.

Well, you may say, but why use computers?  Are they not putting people out
of work.  The answer is very simple, in fact there are several reasons for
using computers, as shown on the next slide.
SLIDE 5
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 accounts 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.

SLIDES

1. Photo of Lady Lovelace  (Frontispiece in Bowden)
2. Quotations fron Lady Lovelace, the British Association, and Marvin Minsky
3. Photo of an abacus
4. Computers vs Calculators.
5. The four parts of a computer.