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Wiring two transistors as you see below in the diagram on the right cre­ ates an OR gate. In the AND gate, the emitter of the top transistor is con­ nected to the collector of the bottom transistor. In the OR gate, the collectors of both transistors are connected to the voltage supply. The emitters are con­ nected together.

OR gate

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AND gate


A In

A In


I B In

Out B In


[ T o

“‘ So everything we learned about constructing logic gates and other com­

ponents from relays is valid for transistors. Relays, tubes, and transistors were all initially developed primarily for purposes of amplification but can be connected in similar ways to make logic gates out of which computers can be built. The first transistor computers were built in 1956, and within a few years tubes had been abandoned for the design of new computers.

Here’s a question: Transistors certainly make computers more reliable, smaller, and less power hungry. But do transistors make computers any sim­ pler to construct?

Not really. The transistor lets you fit more logic gates in a smaller space, of course, but you still have to worry about all the interconnections of these components. It’s just as difficult wiring transistors to make logic gates as it is wiring relays and vacuum tubes. In some ways, it’s even more difficult because the transistors are smaller and less easy to hold. If you wanted to build the Chapter 17 computer and the 64-KB RAM array out of transistors, a good part of the design work would be devoted to inventing some kind of structure in which to hold all the components. Most of your physical labor would be the tedious wiring of millions of interconnections among millions of transistors.



As we’ve discovered, however, there are certain combinations of transis­ tors that show up repeatedly. Pairs of transistors are almost always wired as gates. Gates are often wired into flip-flops or adders or selectors or decoders. Flip-flops are combined into multibit latches or RAM arrays. As­ sembling a computer would be much easier if the transistors were prewired in common configurations.

This idea seems to have been proposed first by British physicist Geoffrey Dummer (born 1909) in a speech in May 1952. “I would like to take a peep into the future,” he said.

With the advent of the transistor and the work in semiconductors generally, it seems now possible to envisage electronic equipment in a solid block with no connecting wires. The block may consist of layers of insulating, conducting, rectifying and amplifying materials, the electrical functions being connected directly by cutting out areas of the various layers.

A working product, however, would have to wait a few years. Without knowing about the Dummer prediction, in July 1958 it occurred

to Jack Kilby (born 1923) of Texas Instruments that multiple transistors as well as resistors and other electrical components could be made from a single piece of silicon. Six months later, in January 1959, basically the same idea occurred to Robert Noyce (1927-1990). Noyce had originally worked for Shockley Semiconductor Laboratories, but in 1957 he and seven other sci­ entists had left and started Fairchild Semiconductor Corporation.

In the history of technology, simultaneous invention is more common than one might suspect. Although Kilby had invented the device six months before Noyce, and Texas Instruments had applied for a patent before Fairchild, Noyce was issued a patent first. Legal battles ensued, and only after a de­ cade were they finally settled to everyone’s satisfaction. Although they never worked together, Kilby and Noyce are today regarded as the coinventors of the integrated circuit, or IC, commonly called the chip.

Integrated circuits are manufactured through a complex process that involves layering thin wafers of silicon that are precisely doped and etched in different areas to form microscopic components. Although it’s expensive to develop a new integrated circuit, they benefit from mass production-the more you make, the cheaper they become.

The actual silicon chip is thin and delicate, so it must be securely packaged, both to protect the chip and to provide some way for the components in the chip to be connected to other chips. Integrated circuits are packaged in a couple of different ways, but the most common is the rectangular plastic dual inline package (or DIP), with 14, 16, or as many as 40 pins protruding from the side:

This is a 16-pin chip. If you hold the chip so the little indentation is at the left (as shown), the pins are numbered 1 through 16 beginning at the lower left and circling around the right side to end with pin 16 at the upper left. The pins on each side are exactly 1/io inch apart.

Throughout the 1960s, the space program and the arms race fueled the early integrated circuits market. On the civilian side, the first commercial product that contained an integrated circuit was a hearing aid sold by Ze­ nith in 1964. In 1971, Texas Instruments began selling the first pocket cal­ culator, and Pulsar the first digital watch. (Obviously the IC in a digital watch is packaged much differently from the example just shown.) Many other products that incorporated integrated circuits in their design followed.

In 1965, Gordon E. Moore (then at Fairchild and later a cofounder of Intel Corporation) noticed that technology was improving in such a way that the number of transistors that could fit on a single chip had doubled every year since 1959. He predicted that this trend would continue. The actual trend was a little slower, so Moore’s Law (as it was eventually called) was modi­ fied to predict a doubling of transistors on a chip every 18 months. This is still an astonishingly fast rate of progress and reveals why home computers always seem to become outdated in just a few short years. Some people believe that Moore’s Law will continue to be accurate until about 2015.

In the early days, people used to speak of small-scale integration, or SSI, to refer to a chip that had fewer than 10 logic gates; medium-scale integration, or MSI (10 to 100 gates); and large-scale integration, or LSI (100 to 5000). Then the terms ascended to very-large-scale integration, or VLSI (5000 to 50,000); super-large-scale integration, or SLSI (50,000 to 100,000); and ultra-large-scale integration, (more than 100,000 gates).

For the remainder of this chapter and the next, I want to pause our time machine in the mid-1970s, an ancient age before the first Star Wars movie was released and with VLSI just on the horizon. At that time, several dif­ ferent technologies were used to fabricate the components that make up inte­ grated circuits. Each of these technologies is sometimes called a family of ICs. By the mid-1970s, two families were prevalent: TTL (pronounced tee tee ell) and CMOS (see moss).

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