Giant brains; or, Machines that think

by Edmund Callis Berkeley

PHYSICAL DEVICES

Now in order for any brain to work, physical devices must be used. For example, in the human body, a nerve is the physical device that carries information from one part of the body to another. In the Harvard machine, an insulated wire is the physical device that carries information from one part of the machine to another. One side of every panel in the Harvard machine is heavily laden with a great network of wires. Between the panels, you can see in many places cables as thick as your arm and containing hundreds of wires. More than 500 miles of wire are used.

The physical devices in the Harvard machine are numerous, as we would expect. It is perhaps not surprising that this machine has more than 760,000 parts. But, curiously enough, there are only 7 main kinds of physical devices in the major part of the machine. They are: wire, two-position switches, two-position relays ([see Chapter 2]), ten-position switches, ten-position relays, buttons, and cam contacts ([see below]). These are the devices that handle information in the form of electrical impulses. They can be combined by electrical circuits in a great variety of ways. There are, of course, other kinds of physical devices that are important, but they are not numerous, and they have rather simple duties. Looking at the machine, you can see three examples easily. Physical devices of the first kind convert punched holes into electrical impulses: 2 card feeds, 4 tape feeds. Those of the second kind convert electrical impulses into punched holes: 1 card punch, 1 tape punch. Those of the third kind convert electrical impulses into printed characters: 2 electric typewriters. We can think of a fourth kind of physical device that would be a help, but, at present writing, it does not yet exist: a device that converts printed characters into electrical impulses.

The Harvard machine, of course, is complicated. But it is complicated because of the variety of ways in which relatively simple devices have been connected together to make a machine that thinks.

Switches

A two-position switch ([see Fig. 2]) turned by hand connects a wire to either one of 2 others. These 2 positions may stand for “yes” and “no,” 0 and 1, etc. There are many two-position switches in the machine. A ten-position switch or dial switch ([see Fig. 3]) turned by hand connects the wire running into the center of the switch with a wire at any one of ten positions 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 around the edge. There are over 1400 dial switches in the machine. How does turning the pointer on the top of the dial make connection between the center wire and the edge wire? Under the face of the dial is the part that works, a short rod of metal fastened to the pointer (shown with dashes in [Fig. 3]). When the pointer turns, this rod also turns, making the desired connection.

Fig. 2.Two-position switch.

Fig. 3. Dial switch.

Relays

Two-position relays—more often called just relays ([see Chapter 2])—do the automatic routing of the electrical impulses that cause computing to take place. Each relay may take 2 positions, open or closed, and these positions may stand for 0 and 1. There are more than 3000 relays in the Harvard machine.

A magnet pulling one way and a spring pulling the other way are sufficient in an ordinary relay to give 2 positions, “on” and “off,” “yes” and “no,” 0 and 1. But how do we make a relay that can hold any one of 10 positions? [Figure 4] shows one scheme for a ten-position relay. The arm can take any one of 10 positions, connecting the contact Common to any one of the contacts O, 1, 2, 3, 4, 5, 6, 7, 8, and 9 so that current can flow. The gear turns all the time. When an impulse comes in on the Pickup line, the clutch connects the arm to the gear. When an impulse comes in on the Drop-out line, the clutch disconnects the arm from the gear. For example, suppose that the ten-position relay is stopped at contact 2, as shown. Suppose that we now pick up the relay, hold it just long enough to turn 3 steps, and then drop it out. The relay will now rest at contact 5.

Fig. 4. Scheme of a ten-position relay,
or counter position.

Fig. 5. Scheme of a
counter wheel.

In the Harvard machine, the ten-position relays, much like the scheme shown, do the same work as counter wheels ([Fig. 5]) in an ordinary desk calculating machine, and so they are often spoken of as counter positions in the Harvard machine. They are very useful in the machine not only because they express the 10 decimal digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 but also because adding and subtracting numbers is accomplished by turning them through the proper number of steps. In fact, an additional impulse is provided when the counter position turns from 9 to 0, for purposes of carry. A group of 24 counter positions makes up each storage counter—or storage register—in the machine. There are 2200 of these counter positions. Each is connected to a continuously running gear on a small shaft ([Fig. 6]). All these shafts are connected by other gears and shafts to a main drive shaft, and they are driven by a 5-horsepower motor at the back of the machine. When a counter position is supposed to step, a clutch connects the drive to the running gear, and the counter position steps. When the counter position is supposed to stay unchanged, the clutch is disconnected and the driving gear runs free. In fact, when you first approach the Harvard machine, about the first thing you are aware of is the running of these gears and the intermittent whirring and clicking of the counter positions as they step. The machine gives a fine impression of being busy!

Fig. 6. Scheme of counter 16.

Timing Contacts

A button ([see Fig. 7]) is a device for closing an electric circuit when and only when you push it. A simple example is the button for ringing a bell: you push the button, a circuit is closed, and something happens. When you let go, the circuit is opened. The Harvard machine has a button for starting, a button for stopping, and many others.

Fig. 7. Button.

Fig. 8. Cam, with 5 lobes and contact.

A cam contact ([see Fig. 8]) is an automatic device for closing an electric circuit for just a short interval of time. When the lobes on the cam strike the contact, it closes and current flows. When the lobes have gone by, the spring pushes open the contact, and no current flows. Just as a two-position relay is the automatic equivalent of a two-position switch, and a ten-position relay is the automatic equivalent of a ten-position switch, so a cam contact is the automatic equivalent of a button.

All the cams in the machine have 20 pockets where small round metal lobes may or may not be inserted. Each cam makes a full turn once in ³/₁₀ of a second and is in time with all the others. Thus we can time all the electrical circuits in the machine in units of ³/₂₀₀ of a second.