In 1948, the Eckert-Mauchly Computer Corporation (later part of Remington Rand) began work on what would become the first commercially available computer-the Universal Automatic Computer, or UNIVAC. It was completed in 1951, and the first one was delivered to the Bureau of the Cen sus. The UNIVAC made its prime-time network debut on CBS, when it was used to predict results of the 1952 presidential election. Walter Cronkite referred to it as an “electronic brain.” Also in 1952, IBM announced the company’s first commercial computer system, the 701.
And thus began a long history of corporate and governmental comput ing. However interesting that history might be, we’re going to pursue an other historical track-a track that shrank the cost and size of computers and brought them into the home, and which began with an almost unno ticed electronics breakthrough in 1947.
Bell Telephone Laboratories was for many years a place where smart people could work on just about anything that interested them. Some of them, for tunately, were interested in computers. I’ve already mentioned George Stibitz and Claude Shannon, both of whom made significant contributions to early computing while working at Bell Labs. Later on, in the 1970s, Bell Labs was the birthplace of the influential computer operating system named Unix and a programming language named C, which I’ll describe in upcoming chapters.
Bell Labs came about when American Telephone and Telegraph officially separated their scientific and technical research divisions from the rest of their business, creating the subsidiary on January 1, 1925. The primary purpose
of Bell Labs was to develop technologies for improving the telephone sys tem. That mandate was fortunately vague enough to encompass all sorts of things, but one obvious perennial goal within the telephone system was the undistorted amplification of voice signals transmitted over wires.
Since 1912, the Bell System had worked with vacuum tube amplification, and a considerable amount of research and engineering went into improv ing vacuum tubes for use by the telephone system. Despite this work, vacuum tubes still left much to be desired. Tubes were large, consumed a lot of power, and eventually burned out. But they were the only game in town.
All that changed December 16, 1947, when two physicists at Bell Labs named John Bardeen (1908-1991) and Walter Brattain (1902-1987) wired a different type of amplifier. This new amplifier was constructed from a slab of germanium-an element known as a semiconductor-and a strip of gold foil. They demonstrated it to their boss, William Shockley (1910-1989), a week later. It was the first transistor, a device that some people have called the most important invention of the twentieth century.
The transistor didn’t come out of the blue. Eight years earlier, on Decem ber 29, 1939, Shockley had written in his notebook, “It has today occurred to me that an amplifier using semiconductors rather than vacuum is in prin ciple possible.” And after that first transistor was demonstrated, many years followed in perfecting it. It wasn’t until 1956 that Shockley, Bardeen, and Brattain were awarded the Nobel Prize in physics “for their researches on semiconductors and their discovery of the transistor effect.”
Earlier in this book, I talked about conductors and insulators. Conductors are so called because they’re very conducive to the passage of electricity. Copper, silver, and gold are the best conductors, and it’s no coincidence that all three are found in the same column of the periodic table of the elements.
As you’ll recall, the electrons in an atom are distributed in shells that surround the nucleus of the atom. What characterizes these three conduc tors is a lone electron in the outermost shell. This electron can be easily dis lodged from the rest of the atom and hence is free to move as electrical current. The opposites of conductors are insulators-like rubber and plastic that barely conduct electricity at all.
The elements germanium and silicon (as well as some compounds) are called semiconductors, not because they conduct half as well as conductors, but because their conductance can be manipulated in various ways. Semi conductors have four electrons in the outermost shell, which is half the maximum number the outer shell can have. In a pure semiconductor, the atoms form very stable bonds with each other and have a crystalline struc ture similar to the diamond. Such semiconductors aren’t good conductors.
But semiconductors can be doped, which means that they’re combined with certain impurities. One type of impurity adds extra electrons to those needed for the bond between the atoms. These are called N-type semi conductors (N for negative). Another type of impurity results in a P-type semiconductor.
Semiconductors can be made into amplifiers by sandwiching a P-type semiconductor between two N-type semiconductors. This is known as an
NPN transistor, and the three pieces are known as the collector, the base, and the emitter.
Here’s a schematic diagram of an NPN transistor:
A small voltage on the base can control a much larger voltage passing from the collector to the emitter. If there’s no voltage on the base, it effectively turns off the transistor.
Transistors are usually packaged in little metal cans about a quarter-inch in diameter with three wires poking out:
The transistor inaugurated solid-state electronics, which means that tran sistors don’t require vacuums and are built from solids, specifically semicon ductors and most commonly (these days) silicon. Besides being much smaller than vacuum tubes, transistors require much less power, generate much less heat, and last longer. Carrying around a tube radio in your pocket was in conceivable. But a transistor radio could be powered by a small battery, and unlike tubes, it wouldn’t get hot. Carrying a transistor radio in your pocket became possible for some lucky people opening presents on Christmas morning in 1954. Those first pocket radios used transistors made by Texas Instruments, an important company of the semiconductor revolution.
The first commercial application of the transistor was, however, a hear ing aid. In commemorating the heritage of Alexander Graham Bell in his lifelong work with deaf people, AT&T allowed hearing aid manufacturers to use transistor technology without paying any royalties. The first transis tor television debuted in 1960, and today tube appliances have almost disappeared. (Not entirely, however. Some audiophiles and electric gui tarists continue to prefer the sound of tube amplifiers to their transistor counterparts.)
In 1956, Shockley left Bell Labs to form Shockley Semiconductor Labo ratories. He moved to Palo Alto, California, where he had grown up. His was the first such company to locate in that area. In time, other semicon ductor and computer companies set up business there, and the area south of San Francisco is now informally known as Silicon Valley.
Vacuum tubes were originally developed for amplification, but they could also be used for switches in logic gates. The same goes for the tran sistor. On the next page, you’ll see a transistor-based AND gate structured
much like the relay version. Only when both the A input is 1 and the B in put is 1 will both transistors conduct current and hence make the output 1. The resistor prevents a short circuit when this happens.