Part 12

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.

By Herbert Goldberg © 1961 Saturday Review

“Is this your trouble?” ]

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“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.

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.