Modern computers are revolutionizing our lives, performing tasks unimaginable only decades ago. This was made possible by a long series of innovations, but there’s one foundational invention that almost everything else relies upon: the transistor. Gokul J. Krishnan describes what a transistor is and how this small device enables all the amazing things computers can do.
Lesson by Gokul J. Krishna, animation by Augenblick Studios.
Lesson by Gokul J. Krishna, animation by Augenblick Studios.
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00:00Modern computers are revolutionizing our lives,
00:10performing tasks unimaginable only decades ago.
00:14This was made possible by a long series of innovations,
00:17but there's one foundational invention that almost everything else relies upon,
00:23the transistor.
00:24So what is that, and how does such a device
00:27enable all the amazing things computers can do?
00:30Well, at their core, all computers are just what the name implies—
00:34machines that perform mathematical operations.
00:37The earliest computers were manual counting devices like the abacus,
00:42while later ones used mechanical parts.
00:44What made them computers was having a way to represent numbers
00:48and a system for manipulating them.
00:51Electronic computers work the same way,
00:53but instead of physical arrangements,
00:55the numbers are represented by electric voltages.
00:58Most such computers use a type of math called Boolean logic
01:02that has only two possible values—the logical conditions true and false,
01:07denoted by binary digits 1 and 0.
01:11They are represented by high and low voltages.
01:14Equations are implemented via logic gate circuits
01:17that produce an output of 1 or 0 based on whether the inputs
01:22satisfy a certain logical statement.
01:25These circuits perform three fundamental logical operations—
01:29conjunction, disjunction, and negation.
01:32The way conjunction works is an AND gate provides a high-voltage output
01:37only if it receives two high-voltage inputs,
01:40and the other gates work by similar principles.
01:43Circuits can be combined to perform complex operations like addition and subtraction,
01:48and computer programs consist of instructions for electronically performing these operations.
01:54This kind of system needs a reliable and accurate method for controlling electric current.
02:00Early electronic computers like the ENIAC used a device called the vacuum tube.
02:05Its early form, the diode, consisted of two electrodes in an evacuated glass container.
02:12Applying a voltage to the cathode makes it heat up and release electrons.
02:17If the anode is at a slightly higher positive potential,
02:20the electrons are attracted to it, completing the circuit.
02:24This unidirectional current flow could be controlled by varying the voltage to the cathode,
02:29which makes it release more or less electrons.
02:33The next stage was the triode, which uses a third electrode called the grid.
02:38This is a wire screen between the cathode and anode, through which electrons could pass.
02:43Varying its voltage makes it either repel or attract the electrons emitted by the cathode,
02:49thus enabling fast current switching.
02:52The ability to amplify signals also made the triode crucial for radio and long-distance communication.
02:59But despite these advancements, vacuum tubes were unreliable and bulky.
03:04With 18,000 triodes, ENIAC was nearly the size of a tennis court and weighed 30 tons.
03:11Tubes failed every other day.
03:13And in one hour, it consumed the amount of electricity used by 15 homes in a day.
03:19The solution was the transistor.
03:21Instead of electrodes, it uses a semiconductor like silicon,
03:25treated with different elements to create an electron-emitting N-type
03:29and an electron-absorbing P-type.
03:32These are arranged in three alternating layers, with a terminal at each,
03:37the emitter, the base, and the collector.
03:40In this typical NPN transistor, due to certain phenomena at the PN interface,
03:45a special region called a PN junction forms between the emitter and base.
03:50It only conducts electricity when a voltage exceeding a certain threshold is applied.
03:56Otherwise, it remains switched off.
03:59In this way, small variations in the input voltage can be used to quickly switch
04:04between high and low output currents.
04:07The advantage of the transistor lies in its efficiency and compactness.
04:12Because they don't require heating, they're more durable and use less power.
04:16ENIAC's functionality can now be surpassed by a single fingernail-sized microchip
04:22containing billions of transistors.
04:24At trillions of calculations per second,
04:27today's computers may seem like they're performing miracles.
04:30But underneath it all, each individual operation is still as simple as the flick of a switch.
04:46They must be champions of the screen.
04:50They're just sendingciamo deaths!
04:52They actually susceptible to the