logic problems, or at least the way they _ought_ to solve them. For
example, a computer might be instructed to select the smallest of three
keys. It would compare A and B, discard the larger, and then compare
with C, finally selecting the proper one. This is of course such a
ridiculously simple problem that few of us would bother to use the
computer since it would take much longer to plot the flow chart than to
select the key by simple visual inspection. But the logical principle is
the same, even when the computer is to be told to analyze all the
business transactions conducted by a large corporation during the year
and advise a program for the next year which will show the most profit.
From the symbolic flow chart, the programmer makes an operational flow
chart, a detailed block diagram, and finally the program itself.
Suitably coded in computer language, this program is ready for the
computer’s control unit.
With a problem of complex nature, such as one involving the firing of a
space vehicle, programmers soon learned they were spending hours, or
even days, on a problem which the computer proceeded to zip through in
minutes or seconds. It was something like working all year building an
elaborate Fourth of July fireworks display, touching the match, and
seeing the whole thing go up in spectacular smoke for a brief moment. Of
course the end justifies the means in either case, and as soon as the
computer has quit whirring, or the skyrockets faded out, the programmer
gets back to work. But some short cuts were learned.
Even a program for a unique problem is likely to contain many
“subroutines” just like those in other problems. These are used and
re-used; some computers now have libraries of programs they can draw on
much as we call on things learned last week or last year.
With his work completed, the programmer’s only worry is that an error
might exist in it, an error that could raise havoc if not discovered.
One false bit of logic in a business problem; a slight mathematical
boner in a design for a manned missile, could be catastrophic since our
technology is so complicated that the mistake might be learned only when
disaster struck. So the programmer checks and rechecks his work until he
is positive _he_ has not erred.
How about the computer? It checks itself too; so thoroughly that there
is no danger of it making a mistake. Computer designers have been very
clever in this respect. One advanced technique is “majority rule”
checking. Not long ago when the abacus was used even in banking, the
Japanese were aware that a single accountant might make a false move and
botch up the day’s tally. But if two operators worked the same problem
and got the same answer, the laws of probability rule that the answer
can be accepted. If the sums do not agree, though, which man is right?
To check further, and save the time needed to go through the whole
problem again, _three_ abacuses, or abaci, are put through their paces.
Now if two answers agree, chances are they are the right solution. If
all three are different, the bank had better hire new clerks!
[Illustration:
_Remington Rand UNIVAC_
A word picture “flow chart” of the logical operation of selecting the
proper key.
]
_Arithmetic or Logic_
Now that our computer has the two necessary ingredients of input and
control, the arithmetic or logic unit can get busy. Babbage called this
the “mill,” and with all the whirring gears and clanking arms his engine
boasted, the term must have been accurate. Today’s computer is much
quieter since in electronic switches the only moving parts are the
electrons themselves and these don’t make much of a racket. Such
switches have another big advantage in that they open and close at a
great rate, practically the speed of light. The fastest computers use
switches that act in _nanoseconds_, or billionths of a second. In one
nanosecond light itself travels only a foot.
The computer may be likened to someone counting on two of his fingers.
Instead of the decimal or ten-base system, most computers use binary
arithmetic, which has a base of two. But fingers that can be counted in
billionth parts of a second can handle figures pretty fast, and the
computer has learned some clever tricks that further speed things up. It
can only add, but by adroit juggling it subtracts by using the
complement of the desired number, a technique known to those familiar
with an ordinary adding machine. There are also some tricks to
multiplying that allow the computer again to simply add and come up with
the answer.
With pencil and paper we can multiply 117 times 835 easily. Remember,
though, that the computer can only add, and that it was once called a
speedy imbecile. The most imbecilic computer might solve the problem by
adding 117 to itself 835 times. A smarter model will reverse the
procedure and handle only 117 numbers. The moron type of computer is a
bit more clever and sets up the problem this way:
835
835
835
835
835
835
835
8350
83500
——
97695
A moment’s reflection will show that this is the same as adding 7 times
835, 10 times 835, and 100 times 835. And of course the computer arrives
at the answer in about the time it takes us to start drawing the line
under our multiplier.
[Illustration:
_The Bendix Corp., Computer Division_
Assembly of printed-circuit component “packages” into computer.
]
Perhaps smarting under the unkind remarks about its mental ability, the
computer has lately been trying some new approaches to the handling of
complex arithmetical problems. Instead of adding long strings of
numbers, it will take a guess at the result, do some smart checking,
adjust its figures, and shortly arrive at the right solution. For
nonarithmetical problems, the computer substitutes yes and no for 1 and
0 and blithely solves problems in logic at the same high rate of speed.
_Memory_
When we demonstrated our superiority earlier in multiplying instead of
adding the numbers in the problem, we were drawing on our memory:
recalling multiplication tables committed to memory when we were quite
young. Babbage’s “store” in his difference engine, you will recall,
could memorize a thousand fifty-digit numbers, a feat that would tax
most of us. The grandchildren of the Babbage machine can call on as many
as a billion bits of information stored on tape. As you watch the reels
of tape spinning, halting abruptly, and spinning again so purposefully,
remember that the computer is remembering. In addition to its large
memory, incidentally, a computer may also have a smaller “scratch-pad”
memory to save time.
Early machines used electromechanical relays or perhaps vacuum-tube
“flip-flops” for memory. Punched-card files store data too. To speed up
the access to information, designers tried the delay-line circuit, a
device that kept information circulating in a mercury or other type of
delay. Magnetic drums and discs are also used. Magnetic tape on reels is
used more than any other memory system for many practical reasons. There
is one serious handicap with the tape system, however. Information on
it, as on the drum, disc, file card, or delay line, is serial, that is,
it is arranged in sequence. To reach a certain needed bit of data might
require running through an entire reel of tape. Even though the tape
moves at very high speed, time is lost while the computer’s arithmetic
unit waits. For this reason the designers of the most advanced computers
have gone to “random access” instead of sequential memory for part of
the machine.
Tiny cores of ferrite material which has the desired magnetic properties
are threaded on wires. These become memory elements, as many as a
hundred of them in an area the size of a postage stamp. Each core is at
the intersection of two wires, one horizontal and one vertical. Each
core thus has a unique “address” and because of the arrangement of the
core matrix, any address can be reached in about the same amount of time
as any other. Thus, instead of spinning the tape several hundred feet to
reach address number 6,564, the computer simply closes the circuit of
vertical row 65 and horizontal row 64, and there is the desired bit of
information in the form of a magnetic field in the selected core.
Hot on the heels of the development of random-access core memories came
that of thin metallic film devices and so-called cryogenic or supercold
magnetic components that do the same job as the ferrite cores but take
only a fraction of the space. Some of these advanced devices also lend
themselves to volume production and thus pave the way for memories with
more and more information-storage capability.
[Illustration:
_International Business Machines Corp._
Magnetic core plane, the computer’s memory.
]
In the realm of “blue-sky” devices, sometimes known as “journalistors,”
are molecular block memories. These chunks of material will contain
millions of bits of information in cubic inches of volume, and some way
of three-dimensional scanning of the entire block will be developed.
With such a high-volume memory, the computer of tomorrow will fit on a
desk top instead of requiring rows and rows of tape-filled machines.
Today, tape offers the cheapest “per bit” storage, and it is necessary
to use the external or peripheral type of information storage. This is
not much of a problem except for the matter of space. Since most
computers are electronic, all that is required to tie the memory units
to the arithmetic unit is wire connections. Douglas Aircraft ties
computers in its California and North Carolina plants with 2,400 miles
of telephone hookup. Sometimes even wires are not necessary. In the Los
Angeles area, North American Aviation has a number of plants separated
by as many as forty miles. Each plant is quite capable of using the
computers in the other locations, with a stream of digits beamed by
microwave radio from one to the other. Information can be transferred in
this manner at rates up to 65,000 bits per second.
_Output_
Once the computer has taken the input of information, been instructed
what to do, and used its arithmetic and memory, it has done the bulk of
the work on the problem. But it must now reverse the procedure that took
place when information flowed into it and was translated into electrical
impulses and magnetic currents. It could convey the answer to another
machine that spoke its language, but man would find such information
unintelligible. So the computer has an output section that translates
back into earth language.
Babbage’s computer was to have printed out its answers on metal plates,
and many computers today furnish punched cards or tape as an output.
Others print the answers on sheets of paper, so rapidly that a page of
this book would take little more than a second to produce! One of the
greatest challenges of recent years is that of producing printing
devices fast enough to exploit fully the terrific speeds of electronic
computing machines. There would be little advantage in a computer that
could add all the digits in all the phone books in the world in less
than a minute if it took three weeks to print out the answer.
Impact printers, those that actually strike keys against paper, have
been improved to the point where they print more than a thousand lines
of type, each with 120 characters in it, per minute. But even this is
not rapid enough in some instances, and completely new kinds of printers
have been developed. One is the Charactron tube, a device combining a
cathode-ray tube, something like the TV picture tube, with an interposed
64-character matrix about half an inch in diameter. Electrical impulses
deflect the electron beam in the tube so that it passes through the
proper matrix character and forms that image on the face of the tube.
This image then is printed electrostatically on the treated paper rather
than with a metal type face. With no moving parts except the paper, and
of course the electrons themselves, the Charactron printer operates
close to the speed of the computer itself, and produces 100,000 words a
minute. This entire book could be printed out in about forty-five
seconds in this manner.
[Illustration:
_Minneapolis-Honeywell,
Electronic Data Processing Division_
A high-speed printer is the output of this computer. It prints 900
_lines_ a minute.
]
There are many other kinds of outputs. Some are in the form of payroll
checks, rushing from the printer at the rate of 10,000 an hour. Some are
simply illuminated numbers and letters on the face of the computer. As
mentioned earlier, the SAGE air defense computer displays the tracks of
aircraft and missiles on large screens, each accurately tagged for
speed, altitude, and classification. The computer may even speak its
answer to us audibly.
General Electric engineers have programmed computers to play music, and
come up with a clever giveaway record titled “Christmas Carols in 210
Time,” à la pipe-organ solo. Some more serious musical work is now being
done in taking a musical input fed to a computer, programming it for
special effects including the reverberant effect of a concert hall, and
having that played as the output.
A more direct vocal output is the spoken word. Some computers have this
capability now, with a modest vocabulary of their own and an extensive
tape library to draw from. As an example, Gilfillan Radio has produced a
computerized ground-control-approach system that studies the radar
return of the aircraft being guided, and “tells” the pilot how to fly
the landing. All the human operator does is monitor the show.
The system uses the relatively simple method of selecting the correct
words from a previously tape-recorded human voice. More sophisticated
systems will be capable of translating code from the computer directly
into an audible output. One very obvious advantage of such an automatic
landing system is that the computer is never subject to a bad day,
nerves, or fright. It will talk the aircraft down calmly and
dispassionately, albeit somewhat mechanically.
These then are the five basic parts of a computer or computer system:
input, control, arithmetic-logic, memory, and output. Remember that this
applies equally to simple and complex machines, and also to computers
other than the more generally encountered electronic types. For while
the electronic computer is regarded as the most advanced, it is not
necessarily the final result of computer development. Let us consider
some of the deviants, throwbacks, and mutations of the computer species.
[Illustration:
_Kearfott Division, General Precision, Inc._
The tiny black box is capable of the same functions as the larger
plastic laboratory model pneumatic digital computer.
Packaging densities of more than 2,000 elements per cubic inch are
expected.
]
_Another Kind of Computer_
We have discussed mechanical, electromechanical, electrical, and
electronic computers. There are also those which make use of quite
different media for their operation: hydraulics, air pressure, and even
hot gases. The pneumatic is simplest to explain, and also has its
precedent in the old player-piano mentioned earlier.
Just as an electric or electronic switch can be open or closed, so can a
pneumatic valve. The analogy carries much further. Some of the basic
electronic components used in computers are diodes, capacitors,
inductors, and “flip-flop” circuits which we have talked of. Each of
these, it turns out, can be approximated by pneumatic devices.
The pneumatic diode is the simplest component, being merely an orifice
or opening through which gas is flowing at or above the speed of sound.
Under these conditions, any disturbance in pressure “upstream” of the
orifice will move “downstream” through the orifice, but any such
happening downstream cannot move upstream. This is analogous to the way
an electronic diode works in the computer, a one-way valve effect.
The electrical capacitor with its stored voltage charge plays an
important part in computer circuitry. A plenum chamber, or box holding a
volume of air, serves as a pneumatic capacitor. Similarly, the effect of
an inductor, or coil, is achieved with a long pipe filled with moving
air.
The only complicated element in our pneumatic computer building blocks
is the flip-flop, or bistable element. A system of tubes, orifices, and
balls makes a device that assumes one position upon the application of
pneumatic force, and the other upon a successive application, similar to
the electronic flip-flop. Pneumatic engineers use terms like “pressure
drop” and “pneumatic buffering,” comparable to voltage drop and
electrical buffering.
A good question at this point is just why computer designers are even
considering pneumatic methods when electronic computers are doing such a
fine job. There are several reasons that prompt groups like the Kearfott
Division of General Precision Inc., AiResearch, IBM’s Swiss Laboratory,
and the Army’s Diamond Ordnance Fuze Laboratory to develop the
air-powered computers. One of these is radiation susceptibility. Diodes
and transistors have an Achilles heel in that they cannot take much
radiation. Thus in military applications, and in space work, electronic
computers may be incapable of proper operation under exposure to fallout
or cosmic rays. A pneumatic computer does not have this handicap.
High temperature is another bugaboo of the electronic computer. For
operation above 100° C., for instance, it is necessary to use expensive
silicon semiconductor elements. The cryogenic devices we talked of
require extremely low temperatures and are thus also ruled out in hot
environments. The pneumatic computer, on the other hand, can actually
operate on the exhaust gases of a rocket with temperatures up to 2000°
F. There may be something humanlike in this ability to operate on hot
air, but there are more practical reasons like simplicity, light weight,
and low cost.
The pneumatic computer, of course, has limitations of its own. The most
serious is that of speed, and its top limit seems to be about 100
kilocycles a second. Although this sounds fast—a kilocycle being a
thousand cycles, remember—it is tortoise-slow compared with the
50-megacycle speed of present electronic machines. But within its
limitations the pneumatic machine can do an excellent job. Kearfott
plans shrinking 3,000 pneumatic flip-flops and their power supply and
all circuitry into a one-inch cube; and packing a medium-size
general-purpose digital computer complete with memory into a case 5-1/2
inches square and an inch thick. Such a squeezing of components surely
indicates _compressed_ air as a logical power supply!
Going beyond the use of air as a medium, Army researchers have worked
with “fluid” flip-flops capable of functioning at temperatures ranging
from minus 100° to plus 7,000° F.! The limit is dictated only by the
material used to contain the fluid, and would surely meet requirements
for the most rigorous environment foreseeable.
The fluid flip-flop operates on a different principle from its pneumatic
cousin, drawing on fluid dynamics to shift from one state to the other.
Fluid dynamics permits the building of switches and amplifiers that
simulate electronic counterparts adequately, and the Army’s Diamond
Ordnance Fuze Laboratory has built such oscillators, shift registers,
and full adders, the flesh and bones of the computer. Researchers
believe components can be built cheaply and that ultimately a complete
fluid computer can be assembled.
The X-15 is cited as an example of a good application for fluid-type
computing devices. The hypersonic aircraft flies so fast it glows, and a
big part of its problem is the cooling of a large amount of electronic
equipment that generates additional heat to compound the difficulty.
Missiles and space vehicles have similar requirements.
Tomorrow’s computer may use liquid helium or a white-hot plasma jet
instead of electronics or gas as a medium. It may use a medium nobody
has dreamed of yet, or one tried earlier and discarded. Regardless of
what it uses, it will probably work on the same basic theory and
principles we’ve outlined here. And try as we may, we will get no more
out of it than we put in.
[Illustration:
By Herbert Goldberg © 1961 Saturday Review
“Is this your trouble?”
]
------------------------------------------------------------------------
“_It is the machines that make life complicated, at the
same time that they impose on it a high tempo._”
—Carl Lotus Becker
4: Computer Cousins—Analog
and Digital
There are many thousands of computers in operation today—in enough
different outward varieties to present a hopeless classification task to
the confused onlooker. Actually there are only two basic types of
computing machines, the analog and the digital. There is also a third
computer, an analog-digital hybrid that makes use of the better features
of each to do certain jobs more effectively.
The distinction between basic types is clear-cut and may be explained in
very simple terms. Again we go to the dictionary for a starting point.
Webster says: “Analogue.—That which is analogous to some other thing.”
Even without the terminal _ue_, the analog computer is based on the
principle of analogy. It is actually a model of the problem we wish to
solve. A tape measure is an analog device; so is a slide rule or the
speedometer in your car. These of course are very simple analogs, but
the principle of the more complex ones is the same. The analog computer,
then, simulates a physical problem and deals in quantities which it can
measure.
Some writers feel that the analog machine is not a computer at all in
the strict sense of the word, but actually a laboratory model of a
physical system which may be studied and measured to learn certain
implicit facts.
[Illustration:
_Minneapolis-Honeywell Computer Center_
A multimillion dollar aerospace computer facility. On left is an array
of 16 analog computers; at right is a large digital data-processing
system.
The facility can perform scientific and business tasks simultaneously.
]
The dictionary also gives us a good clue to the digital computer:
“Digital.—Of the fingers or digits.” A digital machine deals in digits,
or discrete units, in its calculations. For instance, if we ask it to
multiply 2 times 2, it answers that the product is exactly 4. A slide
rule, which we have said is an analog device, might yield an answer of
3.98 or 4.02, depending on the quality of its workmanship and our
eyesight.
The term “discrete” describes the units used by the digital machine; an
analog machine deals with “continuous” quantities. When you watch the
pointer on your speedometer you see that it moves continuously from zero
to as fast as you can or dare drive. The gas gauge is a graphic
presentation of the amount of fuel in the tank, just as the speedometer
is a picture of your car’s speed. For convenience we interpolate the
numbers 10, 20, 30, 1/4, 1/2, and so on. What we do, then, is to convert
from a continuous analog presentation to a digital answer with our eyes
and brain. This analog-to-digital conversion is not without
complications leading to speeding tickets and the inconvenience of
running out of gas far from a source of supply.
A little thought will reveal that even prior to computers there were two
distinct types of calculating; those of measuring (analog) and of
counting (digital). Unless we are statisticians, we encounter 2-1/2 men
or 3-1/2 women about as frequently as we are positive that there is
exactly 10 gallons of fuel in the gas tank. In fact, we generally use
the singular verb with such a figure since the 10 gallons is actually an
arbitrary measurement we have superimposed on a quantity of liquid.
Counting and measuring, then, are different things.
Because of the basic differences in the analog and digital computers,
each has its relative advantages and disadvantages with respect to
certain kinds of problems. Let us consider each in more detail and learn
which is better suited to particular tasks. Using alphabetical protocol,
we take the analog first.
_The Analog Measuring Stick_