All transistors rely on this property, but different types of transistor harness it through different means. This allows regions of the transistor that normally insulate to conduct (or vice versa). By introducing an electric signal to a transistor, electric fields are created that force holes and electrons to swap places. Transistors (portmanteaux of “ transmitter” and “res istor”) rely on a quirk of quantum mechanics known as an “electron hole.” A hole is the lack of an electron at a spot where one could exist in semiconducting material. On average, a tube failed every two days and took 15 minutes to find and replace. Later, the 1946 ENIAC became the first electronic computer capable of solving a large class of numerical problems, also having around 17,000 tubes. The first programmable computer to use vacuum tubes was the 1943 Colossus, built to crack codes during World War II. Because vacuum tubes work so much more quickly than relays, they can keep up with the on/off frequencies used in human speech and music. We can use a low-power signal to operate a very large speaker if we feed the signal into a signal-triggered switch. Understanding how a vacuum tube amplifies is as simple as understanding that a speaker is no more than piece of fabric that moves back and forth depending on whether the wires behind it are on or off. While absent of moving parts, their filaments only worked so long before burning out, and their sealed-glass construction was prone to other means of failure. Vacuum tubes were developed in parallel with light bulbs throughout the 19th century and were first used in an amplifying circuit in 1906. Rather than relying on a magnetic switch, these tubes relied on the “thermionic effect” and resembled dim light bulbs. The successor to the relay was the vacuum tube. On top of that, relays have moving parts, so they are prone to breaking. For this, relay computers need extensive cooling. The problem with relays is that their electromagnets consume a lot of power, and all that wasted energy turns into heat. Notable relay computers included the Z1 through Z3 (1938-1941) and the Harvard Marks I and II (19). While relays have been used since the discovery of the electromagnet in 1824 - particularly by the 1837 invention of the telegraph - they would not be used for computation until the 20th century. While this method of information storage has taken a back seat to magnetic and optical media, it is still important to some modern computer operations such as cache. Through looping signals backwards, certain kinds of memory are made possible by signal-triggered switches as well. All calculators and computers achieve their mystical power through this method. The only limit to our computing power is how many signal-triggered switches we can use. Similar circuits can be constructed for all sorts of calculations, including addition, subtraction, multiplication, division, conversion between binary (base 2) and decimal (base 10), and so on. Understanding that XOR behavior is what enables us to "carry the 10" when doing addition, it becomes clear why signal-triggered switches are so vital to computation. "Boolean XOR" switch (Image credit: Robert Coolman)
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