Prior to the use of purely electronic devices in computers, electro-mechanical devices were used. These electro-mechanical devices include cards for entering programs and data, and switch relays for calculations. Classic example of these are the very first computers known to us.
Of course, this type of machine is bulky, expensive, difficult to run and to maintain. A such, very few owns such computers.
The next step in computer development is the use of electronic switch.
Simplistically, electronic switches allow the pesence or abscence of a voltage
on one circuit to control current flow on another circuit ; The first
electronic switches are thermionic valves, more popularly known as tube.
However, like their predecessors, valves have several drawbacks. First, it
operates at very high temperature. It consumes a lot of power. Secondly,
although valves can last for more than eight years, its MBTF (mean time between
failure) is around 25000 hours. At the current standard, that is still very
high! ENIAC is the world's first electronic computer. It was built out of
tubes and filled one whole room !
Rapid development in electronics
quickly replaced tubes with transistors. Transistors are smaller and require
leser power but it still make a very large computer. Interconnections are
also a problem. There are simply many joints to join and solder ! On
the average, it makes expensive, unreliable computer.
The advent of integrated circuits (IC) in the 1950s changed the pace of computer development. Essentially, ICs are still a type of transistor; several transistors with their interconnections already made, are etched onto a single chip of silicon. Structures on the silicon are made by evaporating or sputtering aluminum on the surface of a silicon chip. Impurities like boron, phosphorus, or arsenic are added with silicon to improve its conductivity, while isolation between structures are provided by silicon dioxide (SiO2).
The transistor itself is invented in 1947, while the first practical IC was fabricated in 1959 at Fairchild. Texas Instrument and Fairchild began manufacturing ICs commercially in 1961. Develoment in manufacturing technology made possible the doubling of number of transistors placed on each chip of silicon. In fact, medium scale integration (MSI) chips came out in 1968, and two years later, the LSI followed. As you would have guessed, this finally led to the development of microprocessors.
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