Derek: The modern era of electronics began with the light bulb, but not in the way you might think. Early light bulbs consisted of a carbon filament sealed inside a glass bulb with a vacuum inside. When a potential difference was applied across the filament, current flowed through it, heating it up to over 2000 Kelvin, so hot that it glowed. Thomas Edison noticed that over the bulb’s lifetime, the glass became discolored, turning yellow, then brown, but only on one side. This phenomenon, known as thermionic emission, was the breakthrough for the electronics revolution. It allowed for the emission of electrons off a hot filament which were unobstructed because they were in a vacuum.
John Ambrose Fleming patented a device that was very similar to Edison’s light bulb, but with one important addition: a second electrode in the bulb. By charging this plate positively with respect to the filament, electrons could be accelerated across the gap, completing the circuit. This device was called a thermionic diode and it was used initially for detecting radio signals, but it could also convert alternating current to direct current.
Combining a few diodes and a capacitor led to a fairly steady direct current, and this was a big deal. It was the first practical vacuum tube device and the model for all vacuum tubes that would dominate the industry for the next half century. In the early 1900s, the big problem in electronics was amplification. Radio had just been invented but its range was limited by the lack of reliable equipment that could boost weak signals. Similarly, telephone calls were limited to at most 1300 kilometers because by that point, the signal was too faint to hear.
Rudimentary forms of amplification had been built for telegraph operation called the relay. However, its binary output means it’s incapable of amplifying the complex and analog signals of phone calls and radio waves.
The modern era of electronics began with the light bulb, but not in the way you might think. Early light bulbs consisted of a carbon filament sealed inside a glass bulb with a vacuum inside. When a potential difference was applied across the filament, current flowed through it, heating it up to over 2000 Kelvin, so hot that it glowed. Thomas Edison noticed that over the bulb’s lifetime, the glass became discolored, turning yellow, then brown, but only on one side. This phenomenon, known as thermionic emission, was the breakthrough for the electronics revolution.
John Ambrose Fleming patented a device that was very similar to Edison’s light bulb, but with one important addition: a second electrode in the bulb. By charging this plate positively with respect to the filament, electrons could be accelerated across the gap, completing the circuit. This device was called a thermionic diode and it was used initially for detecting radio signals, but it could also convert alternating current to direct current.
Combining a few diodes and a capacitor led to a fairly steady direct current, which was a big deal. It was the first practical vacuum tube device and the model for all vacuum tubes that would dominate the industry for the next half century. In the early 1900s, the big problem in electronics was amplification. Radio had just been invented but its range was limited by the lack of reliable equipment that could boost weak signals. Similarly, telephone calls were limited to at most 1300 kilometers because by that point, the signal was too faint to hear. Rudimentary forms of amplification had been built for telegraph operation called the relay, but its binary output means it’s incapable of amplifying the complex and analog signals of phone calls and radio waves. If either switch A or B is closed, so adding 0 + 1 or 1 + 0, then current flows through the circuit and the output light would light up.And if both switches were closed, so adding 1 + 1, then current flows through the circuit and both the output and carry lights would light up.So with this device, Stibitz had just built the first digital computer. The beginning of the digital age was not glamorous. Stibitz built his device out of a few batteries, light bulbs, and relays he had lying around. He even cut up a tin of tobacco for the inputs. Built in one night at his kitchen table, the circuit became known as the Model K. This circuit is now called a half adder and was composed of electrical versions of Boolean operators, XOR and AND. It is possible to build other Boolean operators as electronic gates for OR, NOR, and NAND. This circuit tricked electrons into doing simple math, and when combined with other half adders, more complex math could be done.
Two years later, the Model I was built with more than 400 relays and could add two eight digit numbers together in a 10th of a second. It could also multiply eight digit numbers and do multiplication of complex numbers, though these operations took longer.
Over the next 10 years, six more computers based on relays were built and used by the US military and NACA (later NASA). However, the mechanical nature of the relays and their tendency to break made it clear that this was not the future of computers. It’s a great way to learn the basics of how the Internet, software, and hardware all fit together.
Anytime you have something that’s mechanical, it’s gonna wear down. Every time that relay switches, there’s a little bit of friction on the rotation point inside of there and there’s contacts that are making and breaking electrical connections, and those are gonna wear out. So it doesn’t really work in a business environment all that well. You can’t really stuff it into your office that you’re gonna drive people insane.
What computer scientists really needed was an electronic switch and that is where the vacuum tube triode comes in. Whoa! I mean, sure it can work as an amplifier if you put slightly positive or negative voltages on the grid, but it can also work as a switch. If the grid voltage is very negative, then no current flows. And if the grid voltage is very positive, then maximum current flows. So a triode can be controlled using no moving parts. Just a voltage will set it to be either a 0 or a 1. And best of all, switching between the two can be done rapidly with no noise since you’re just controlling electrons zipping around in a vacuum. This is the invention that took computing to the next level.
The world’s first electronic programmable computer was called ENIAC and it came online for the first time on December 10th, 1945. It took up a whole room, weighed 30 tons, and used 175 kilowatts of power. So much that it led to a rumor that every time it turned on, the lights in Philadelphia, where ENIAC was located, would dim. Now, that was just a rumor, but mainly because ENIAC had its own dedicated electrical generator to keep up with the enormous power draw.
Unlike previous computers, ENIAC wasn’t limited to just solving one type of mathematical problem. It could be programmed and it was fast, completing 500 operations per second. At the time, the word computers still referred to people doing calculations with pen and paper. So 500 operations per second was really fast. ENIAC’s flexibility and power was immediately useful for the development of the hydrogen bomb. The computations needed were so complex that the director of Los Alamos at the time said that, “It would’ve been impossible to arrive at any solution without the aid of ENIAC.”
This is a hilarious part bout having a processor that is 1 meter tall and 70 centimeters wide, is that you can point at actual parts of the processor. This is what a 1-bit vacuum tube computer looks like. Can you feel the heat coming off of it? I certainly can. I can feel the heat coming off. It’s getting warm. Well, I mean, 190 vacuum tubes is a lot. I think we figured it out. This is pulling like 350 or 400 watts of power or something like that, which is absurd. At night, it’s awesome. It looks like a city.
But there were also major flaws with vacuum tubes. The filaments always needed to be heated, so they used a lot of power even when idle, and they were big. It was hard to make a glass vacuum tube with complex electrodes inside arbitrarily small. They were also unreliable. On average, a vacuum tube in ENIAC broke down every few days. And then, it needed to be found and replaced. The longest that ENIAC operated for without failure was just 116 hours.
The first digital computers ran on glorified light bulbs. That is why they were so big, power-hungry, and unreliable. The miracle and what has made our modern lives possible is that someone figured out how to perform the same trick with electrons inside a solid piece of material, in silicon. But that’s a story for another day.
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