Microcomputer Circuits and Processes

CHAPTER 1
A HISTORY OF THE
MICROPROCESSOR
SOWING
THE SEEDS
The revolution now shaking every aspect of life from banking and
medicine to education and home life began in 1947 in the Bell
Laboratories with the invention of the transistor by Brattain, Bardeen,
and Shockley. This small amplifier (which now in modern memory
circuits can be made very small- 6 Ilm x 6 Ilm) quickly replaced the
large power-consuming vacuum tube. The evolution of the microprocessor
from the humble transistor illustrates the relationship between
technology and economics, and also how the technology of electronic
device production is related to the desired applications of electronics at
any time.
For example, it is difficult to build a practical computer which needs
a large number of switching circuits using vacuum tubes. But when the
transistor was invented, the situation at once changed. In the 1950s the
transistor did replace vacuum tubes in many applications, but as far as
building computers was concerned, there still remained the problem of
the myriad of connections which had to be made between individual
transistors. That meant time and materials. Also, studies made in the
early 1950s suggested that only 20 computers would be needed to
satisfy the World's needs. The market did not exist, and technology was
then unable to stimulate it. The solution to the interconnection problem
was the integrated circuit, invented by Jack Kilby of Texas Instruments
in 1958, and Bob Noyce, at Fairchild in 1959.
THE INTEGRATED CIRCUIT INDUSTRY
Manufacturing an integrated circuit (IC) involves the 'printing' of many
transistors, with a sprinkling of resistors and capacitors, on to a wafer of
silicon. Those in the trade call this printing process photolithography
and solid-state diffusion. Using this technology, hundreds of very small,
identical circuits can be made simultaneously on one wafer of silicon.
These circuits are bound to be cheap. But most important is the ability
to print the interconnections between the individual transitors on to the
silicon chip, removing the need for manually wiring the circuit together.
So costs were"again reduced. As reliability of the circuits improved
dramatically, so maintenance costs fell too.
Such economic trends inspired manufacturers to research into
further miniaturization, and in 1965, Gordon Moore, later chairman of
Intel Corporation, predicted that during the next decade the number of
transistors per integrated circuit would double every year. This exponential
'law' held good, and remained good into the 1980s.The graph
in figure 1.1shows this law, from the first IC of 1959containing just one
1