Vacuum tube

Glass vacuum tubes used in early computers were fragile and took up space.

Computer chip

In 1974, the first computer microchip con tained 6000 transistors. Today, more than 40 million transistors can be placed on a single computer chip.

Diode

In a diode, a layer of p-type silicon is joined to a layer of n-type silicon. When the leads on a diode are correctly connected in a circuit, electrons flow toward the junction between the two types of silicon. Electrons from the n-type silicon fill holes in the p-type silicon. In devices that use batteries, a diode can keep electrons from flowing if the batteries are not inserted correctly. Some diodes emit light when the circuit is complete.

Transistor

In a transistor, there are three layers of doped silicon. There is a layer of p-type silicon sandwiched between two layers of n-type silicon or a layer of n-type silicon between two layers of p-type silicon. Transistors are used to amplify current. A small current applied to the central layer of a transistor can produce a larger current.

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