File: etc/babbage - item number: 0
[Mike James starts a new series looking at the great ideas of computing
and where they come from.]
You can't start with a bigger topic than "the computer" but it is such a
commonplace that we tend to take it for granted and miss how truly
amazing it is. Some of the readers of Shopper were born before the era
when computers were on every desktop, others have never known it any
other way. So fast are things progressing that ideas that once seemed
rare and extraordinary are now so obvious that we never delve any deeper
into them. For example, what exactly is a computer? What makes it
different from all of the other machines that we use today and have used
in the past?
A computer clearly is unique and usually easy to spot, because it is a
machine that does no useful work! This may seem like a cruel joke
thought up by someone who knows computers, the P C in particular, all
too well, but it is 100 percent true. In physics, work is only done
when a force moves its point of application through a distance, so steam
engines and motor cars do useful work, but a computer just gets warm.
Yes, all those power stations work day and night polluting the
atmosphere just to keep your P C warm. More seriously, the fact that
computers get warm is just a sign that we haven't quite got it right
even now. In theory there is absolutely no reason why a computer should
get hot at all--but that's another story.
So a computer is a machine that does no useful work--but this only
narrows it down. After all, a T V and a telephone satisfy the same
condition, and so do most electronic devices. Clearly a computer is a
bit more than either of these two devices, so what is the essence that
makes it so different? To answer that question we have to go back in
time, but not as far back as you might think ...
Is a computer a calculator? Long before a recognisable computer was
made, there were calculators--mechanical devices, usually based on cogs
and gears, that performed the four basic arithmetic operations. The
calculator is an essential machine that is to be found today as a
desktop accessory on most computers. The fact that our computers create
a virtual calculator should give you a clue that the two are not really
the same type of machine. There were even calculators that worked with
non-numeric problems.
After Boole invented symbolic logic in 1854, William Stanley Jevons was
inspired to build "the Logical Piano". This was a collection of cogs
and gears that didn't crunch numbers but Boolean logic. You entered an
expression with And, Or and Not and it told you if the whole thing was
true or false. Later machines were built that could solve much more
complex problems of the sort found in puzzle books, but even these
impressive machines are not computers.
Loom Service.
It is often said that a forerunner of the computer was the Jacquard
loom, because it used punched cards to control the patterns it wove into
the cloth. This is mostly nonsense, although it clearly influenced the
early thinkers about computers, and it was used as a more concrete
example of what they were trying to explain to an otherwise
uncomprehending public. It is difficult to explain what a computer is
when you don't have one to point at. The Jacquard loom was even said to
be "programmable" in the same way as a computer, because you could alter
the punching of the cards to get different patterns. It could even
claim to be the first to invent the program loop, because by sticking
the front of the first card to the end of the last card the machine
could run without break. All nonsense.
The Jacquard loom is just an example of advanced automaton. The
production of machines that followed set patterns of behaviour as
controlled by slotted metal sheets, metal rods or oddly shaped wheels
has a long history. The Jacquard loom is just another and its only
claim to fame is that the control mechanism was easily altered because,
instead of metal, it used thick cardboard.
There is simply no avoiding the fact that the computer idea was
Babbage's (hence the name of this series). We think of him as the man
responsible for the impressive machines of cogs and gears that seem just
right for the Victorian age, but Babbage should be remembered for his
idea and not his failure to build it. He started out with the idea of
building an advanced calculator, but somewhere along the way he stumbled
on the idea of a computer. In 1833 he started to design the machine
that we know as the Analytical Engine. In fact, there wasn't a
definitive design, because he revised and improved it throughout his
life.
It is easy to be astonished at the physical details of the machine that
his plans describe. It was huge and mechanical, but you can identify
all of the parts of a modern computer. There's the mill, a mechanical
central processor, the store, early RAM, and punched cards held the
program. The whole thing was as large as a steam engine and needed one
to drive its cogs and gears round. When the program was complete a
lever rang a bell. As I said, an impressive machine, and it's easy to
see it as an amusing Heath Robinson construction or something to revere
as a brass and bronze art work. In fact the machine itself isn't the
point.
Ghost in the machine:
The point is that Babbage had described a new type of machine and a new
operating principle that could be applied to a whole class of machines,
irrespective of what they were made of. Babbage had invented the
programmable computer, as opposed to the loom or any other programmable
machine. The key difference is that the program specifies what should
be done with information stored in its memory and not how some part
should move. If you like, it is the meeting of the calculator and the
automaton--the Jevons Logical Piano meets the Jaquard loom! The
"things" being manipulated are just states of the machine, and these
states represent some aspect of the outside world--like the height of
the tide at a particular time or the amount of money in your account.
No useful work is done because what is being manipulated is information,
not material. The first programmer, Augusta Ada King, said: "We may
say most aptly that the analytical engine weaves algebraic patterns just
as the Jacquard loom weaves flowers and leaves". Usually this is
interpreted as a statement of how similar the two were, but it is better
seen as a statement of how different they were.
You can take Babbage's idea even further--who needs a real machine?
Alan Turing didn't, even though he is best known for his "Turing
Machine" and perhaps a little less well known for the Ace computer he
designed. This, like the suggestion that Babbage was a failure, is a
misunderstanding. Turing's legacy is the idea that the computer is an
idea, a thing of the mind and not just a particular realisation of it.
Turing's machine (1936) was a simple paper description of the absolute
minimum that was needed for a computer to be a computer. It was
essentially nothing more than a strip of paper, a pen and a list of
instructions. The pen could write on the paper and the number it wrote
could be read as input to the machine. At the time the word "computer"
meant a person who did computations. Rooms full of people spent their
days doing sums, and being a "computer" was a respectable profession.
Presumably this is where Turing got his inspiration for the
paper-and-pen approach to computing!
Strip tease:
Turing's machine was the ultimate in stripped-down computing, but
surprisingly, while it could take an unreasonable amount of time to do
an particular task, Turing proved that nothing was beyond its
capabilities if you were prepared to wait. To be more precise, he
proved that his machine was universal in the sense that it could do
anything that any other computer could do. He did this by showing that
it was possible to write data on the paper tape which would make the
Turing machine behave like any other computer--yes, an imaginary machine
creating a virtual one.
The argument still rages over who built the first computer, and it seems
reasonable that some of the people involved can also lay claim to having
reinvented the computer idea without help from Babbage. His work was so
little known at the start of the 20th century that most computer
pioneers, Turing for one, knew little about it. However, the actual
building of a computer is clearly a matter of engineering. The original
idea was obviously Babbage's, refined by Turing.
One of the people often credited with taking Babbage's idea further is
John Von Neumann. He wrote a theoretical specification for a computer
after being told about the Eniac--usually credited as the first
electronic computer. Von Neumann's claim to fame is that he thought up
the idea of storing the program along with the data--the so-called
stored program or Von Neumann architecture. Clever, but of course
Turing's universal machine contained the same idea when it used the data
written on its tape to specify not only the program but the machine to
run it!
So far we haven't really defined what essential computer idea is. We've
talked around it, said what it isn't but it still remains slightly
elusive, slightly shadowy. The reason is that it really is quite a
subtle idea and it is difficult to explain it without reference to the
particular technology used to realise it. To take the example of George
Stephenson and the "moving machine", you can see that it is easier to
give examples, carts, chariots, cars, steam engines and so on than it is
to capture the essence of what a "moving machine" is. A computer
clearly has to have a program--I E a list of instructions that controls
what it does--but there is one extra condition. A computer is a
programmable machine that manipulates symbols. The Jaquard loom is a
programmable machine, but what it turns out is cloth and not symbols. A
calculator manipulates symbols, but it has to be programmable before it
approaches the status of computer.
So now we have a wonderful abstract definition of what is and what is
not a computer, but in the real world the engineering matters. It took
many years and many clever ideas to turn the crude internal combustion
engine into something that cruises the motorways at the speed limit.
The same is true, only more so, of the computer. Turing may have had an
imaginary computer, but you couldn't use it to play Doom or run Windows
95. To make the modern computer work, you need lots of clever ideas to
determine how to implement Babbage's mill, store and input-output
devices. Beyond this you also need to know how to make the symbols do
what you want them to and do it reliably. Both involve great ideas that
are essential to understanding what your computer can and cannot do
today.
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(Monday, 23 February, 2026.)