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You'd probably want to use a better oscillator as well. While you can certainly connect the output of a TTL inverter to the input, it's better to have an oscillator with a more predictable frequency. Such an oscillator can be constructed fairly easily using a quartz crystal that comes in a little flat can with two wires sticking out. These crystals vibrate at very specific frequencies, usually at least a million cycles per second. A million cycles per second is called a megahertz and abbreviated MHz. If the Chapter 17 computer were constructed out of TTL, it would probably run fine with a clock frequency of 10 MHz. Each instruction would execute in 400 nanoseconds. This, of course, is much faster than anything we conceived when we were working with relays.

The other popular chip family was (and still is) CMOS, which stands for complementary metal-oxide semiconductor. If you were a hobbyist designing circuits from CMOS ICs in the mid-1970s, you might use as a reference source a book published by National Semiconductor and available at your local Radio Shack entitled CMOS Databook. This book contains information about the 4000 (four thousand) series of CMOS ICs.

The power supply requirement for TTL is 4.75 to 5.25 volts. For CMOS, it's anything from 3 volts to 18 volts. That's quite a leeway! Moreover, CMOS requires much less power than TTL, which makes it feasible to run small CMOS circuits from batteries. The drawback of CMOS is lack of speed. For example, the CMOS 4008 4-bit full adder running at 5 volts is only guaranteed to have a propagation time of 750 nanoseconds. It gets faster as the power supply gets higher—250 nsec at 10 volts and 190 nsec at 15 volts. But the CMOS device doesn't come close to the TTL 4-bit adder, which has a propagation time of 24 nsec. (Twenty-five years ago, the trade-off between the speed of TTL and the low power requirements of CMOS was fairly clear cut. Today there are low-power versions of TTL and high-speed versions of CMOS.)

On the practical side, you would probably begin wiring chips together on a plastic breadboard:

Each short row of 5 holes is electrically connected underneath the plastic base. You insert chips into the breadboard so that a chip straddles the long central groove and the pins go into the holes on either side of the groove. Each pin of the IC is then electrically connected to 4 other holes. You connect the chips with pieces of wires pushed into the other holes.

You can wire chips together more permanently using a technique called wire-wrapping. Each chip is inserted into a socket that has long square posts:

Each post corresponds to a pin of the chip. The sockets themselves are inserted into thin perforated boards. From the other side of the board, you use a special wire-wrap gun to tightly wrap thin pieces of insulated wire around the post. The square edges of the post break through the insulation and make an electrical connection with the wire.

If you were actually manufacturing a particular circuit using ICs, you'd probably use a printed circuit board. Back in the old days, this was something a hobbyist could do. Such a board has holes and is covered by a thin layer of copper foil. Basically, you cover all the areas of copper you want to preserve with an acid resistant and use acid to etch away the rest. You can then solder IC sockets (or the ICs themselves) directly to the copper on the board. But because of the very many interconnections among ICs, a single area of copper foil is usually inadequate. Commercially manufactured printed circuit boards have multiple layers of interconnections.

By the early 1970s, it became possible to use ICs to create an entire computer processor on a single circuit board. It was really only a matter of time before somebody put the whole processor on a single chip. Although Texas Instruments filed a patent for a single-chip computer in 1971, the honor of actually making one belongs to Intel, a company started in 1968 by former Fairchild