1.5 INTEGRATED CIRCUITS

Our world is full of integrated circuits (semiconductor devices with several transistors built into one physical component). It is an electronic circuit which involves thousands or millions of interconnected components like transistors, diodes and resistors. They are usually called ICs. We can find several of them in computers. For example, most people have probably heard about the microprocessor. The microprocessor is an integrated circuit that processes all information in the computer.

It keeps track of what keys are pressed and if the mouse has been moved. It counts numbers and runs programs, games and the operating system. The first integrated circuits (ICs) were based on small scale integration (SSI) circuits, which had around 10 devices per circuit (or „chip‟), and evolved to the use of medium-scale integrated (MSI) circuits, which had up to 100 devices per chip. Integrated circuits are also found in almost every modern electrical device such as cars, television sets, CD players, cellular phones, etc. The main benefits of ICs are lower costs, high reliability and smaller space requirements. But what is an integrated circuit and what is the history behind it? 

1.5.1 Electronic Circuits 

The integrated circuit is nothing more than a very advanced electric circuit. An electric circuit is made from different electrical components such as transistors, resistors, capacitors and diodes, which are connected to each other in different ways. It is an unbroken loop of conductive material that allows electrons to flow continuously. If a circuit is “broken”, its conductive elements will no longer form a complete path and continuous electron flow cannot occur. The transistor acts like a switch. It can turn electricity on or off, or it can amplify current. It is used for example in computers to store information. 

The resistor limits the flow of electricity and gives us the possibility to control the amount of current that is allowed to pass. For example resistors are used, among other things, to control the volume in television sets or radios. 

The capacitor collects electricity and releases it all in one quick burst. The diode stops electricity under some conditions and allows it to pass only when these conditions change. This is used in, for example, photocells where a light beam that is broken triggers the diode to stop electricity from flowing through it. 

The flashlight is an example of electric circuits. It contains electrical energy (dry cells) as a source, a load (the bulb) which changes the electrical energy into light and a switch to control the energy delivered to the load. 

1.5.2 The Transistor vs. the Vacuum Tube 

The transistor is the most important one for the development of modern computers. Before the transistor, engineers had to use vacuum tubes. Just as the transistor, the vacuum tube can switch electricity on or off, or amplify a current. So why was the vacuum tube replaced by the transistor? There are several reasons.The vacuum tube looks and behaves very much like a light bulb; it generates a lot of heat and has a tendency to burn out. Also, compared to the transistor it is slow, big and bulky. When engineers tried to build complex circuits using the vacuum tube, they quickly became aware of its limitations. The first digital computer ENIAC, for example, was a huge monster that weighed over thirty tons, and consumed 200 kilowatts of electrical power. It had around 18,000 vacuum tubes that constantly burned out, making it very unreliable. When the transistor was invented in 1947 it was considered a revolution. Small, fast, reliable and effective, it quickly replaced the vacuum tube.