Why The First Computers Were Made Out Of Light Bulbs

- The modern era of electronics began with the

light

bulb, but not in the way you might think. The

first

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 to over 2000 Kelvin, so hot that it glowed. If there had been too much oxygen in the bulb, the filament would have burned out immediately. That was the reason for the emptiness. But from the perspective of electronics, the real breakthrough came from a curious observation

made

by Thomas Edison.

He saw that during the life of a light bulb, the glass would discolor, turning yellow and then brown, but only on one side. So what was happening? Well, the heated filament not only emits light and heat but also electrons. You can imagine them boiling on the surface of the charcoal. This phenomenon, known as thermionic emission, had been discovered twice independently by other scientists up to 27 years earlier. But after Edison, it became widely known. In fact, for a time, the emission of electrons from a hot filament was called the Edison effect. Now, these floating electrons were not obstructed because they are in a vacuum.

But since there was a potential difference between the wires leading to the filament, the electrons were attracted to the positive wire. So they accelerated towards it and most of it flew past and crashed into the glass, discoloring it over time only on the bright side. I should point out that Edison was using DC electricity. If he had been using air conditioning, both sides would have been discolored. But it was this observation that set the stage for an electronic revolution and, eventually, for the

first

digital

computers

. In 1904, John Ambrose Fleming patented a device very similar to Edison's light bulb, but with an important addition: a second electrode in the light bulb.

By charging this plate positively with respect to the filament, the electrons could be accelerated through the gap, completing the circuit. But if the plate were slightly negative relative to the filament, then it would repel electrons and no current would flow. Fleming called his device a one-way street for electricity. Since only one of the electrodes was heated, the electrons could only flow from there to the plate and not the other way around. The device was called thermionic diode and was initially used to detect radio signals, but it could also convert alternating current to direct current. Scientists quickly realized that a more efficient design had the filament in the center and the other electrode on the plate or anode as a cylinder surrounding it.

This geometry captured more electrons leaving the filament and allowed larger currents to flow. - Ah, there it goes. - With just one of these diodes, you could turn AC into a kind of bumpy DC. But the combination of a few diodes and a capacitor generated a fairly stable direct current, and this was a big problem. 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. At the beginning of the 20th century, 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 amplify weak signals.

Likewise, telephone calls were limited to a maximum of 1,300 kilometers because at that time the signal was weak and could barely be heard. A rudimentary form of amplification had been built for telegraph operation called relay. In a relay there is an electromagnet. And when current flows through that electromagnet, it attracts a switch that turns on a second circuit. But when the current through the electromagnet stops, the switch is released and the second circuit opens again. This device works well for amplifying the dots and dashes of Morse code along a telegraph line, but its binary output means it is unable to amplify complex, analog signals from telephone calls and radio waves.

And that's why a breakthrough came in 1906 when Lee de Forest took the diode and added another electrode to the light bulb. This electrode was not a solid piece of metal but rather a sparse wire mesh and was placed between the filament or cathode and the anode. With three electrodes, it was called a triode. Now, a large potential difference could be applied between the anode and cathode, but the amount of electrons that actually flowed between them was controlled by the voltage on the grid, as this new electrode was known. If the grid had a slightly negative charge, it repels the electrons from the filament so that none can flow to the anode.

But if the grid were slightly positive, then the electrons would be attracted out of the filament and most of them would pass through the holes in the grid and then accelerate towards the anode. In this way, a small voltage change in the grid can control a huge voltage at the anode and the response is fast. So you can get high frequency amplification. I like to think I'm on top of a cliff, opening and closing a valve on a large water pipe. I mean, it doesn't take much energy to turn the valve, but that little inlet turns into a huge outlet of water pouring over the cliff. - You're boosting this track here. - Warming up, you can see it warming up there. - So yellow is the entrance? - Yellow is the entrance.

Purple is the result. Basically we have a two volt change in the input that gives us, what is this? Five volts, that is, five, 10, 15 volts change at the output. - For this demonstration, we only use 24 volts at the anode. If we had used a higher voltage we could have gotten a lot more amplification and people did. This was the device that allowed us to make long distance calls for the first time. Using vacuum tubes, the first transcontinental call from New York to San Francisco took place on January 25, 1915. - Wow. - Yes, there we go, it should be 10 volts. - It's hard to see the grid here because just like with the cylindrical diode, the best configuration for a triode is to have a cylindrical configuration.

The anode is on the outside, the grid is cylindrically on the inside, and the cathode or filament is in the center. The invention of the triode was incredibly important. Radios, televisions, and any electronic devices people had ran on vacuum tubes. You would have had so many in your home even until the 1960s and 1970s. But vacuum tubes did not finish revolutionizing electronics. In his 1937 thesis, Claude Shannon found a connection between electrical circuits and a branch of mathematics known as Boolean algebra. Working in the mid-19th century, George Boole was trying to find a mathematical basis for logic.

Under his system, a true statement was represented as a 1 and a false statement as a 0. And Boole also developed some operations like AND. If both statements A and B were true, then the result would also be true. What Shannon realized was that Boolean operations could be represented as electronic circuits, that there was an equivalence between mathematical statements and electrical circuits. All you needed to make these circuits in the real world were a couple of switches. That same year, 1937, George Stibitz built the first digital calculator. You could add two 1-bit binary numbers. That is, it could add two numbers as long as they were 0 or 1.

The calculator worked through a relay, that electromechanical switch of telegraphy. There were two entries. If they were left open, the input was 0. If they were closed, it was a 1. The output was shown with two light

bulbs

. If there were no lights on, the answer was 0. If the exit light was on, the answer was 1. And if the transport light was on, the answer was 2. The circuit diagram works like this. If neither switch A nor switch B is closed, adding 0 + 0, then no current flows through the circuit and no light bulb will light. But if input A were closed, current would flow through the solenoid, creating a magnetic field that closes the switch inside it, and this connects the output bulb to current and disconnects the transport bulb.

Then the output light bulb turns on, meaning the response is 1. And the same would happen when input B was closed and A was open. But if you closed A and B simultaneously, then no current will flow through the solenoid, but current will flow from the battery connected to A, which is connected to the transport bulb. It then lights up indicating that 1 + 1 equals 2. This is the beginning of the digital age and no, it was not glamorous. Stibitz built his device with some batteries, light bulbs and relays he had lying around. And for supplies, he cut a can of tobacco.

He built it in one night on his kitchen table, which is why it became known as Model K. The circuit that Stibitz built is now called a half-adder. But if you look at the circuit through the eyes of Claude Shannon, you realize that it is actually a pair of logic gates. The output bulb must turn on when A or B, but not both, are closed, so this is known as an exclusive OR gate. While the transport bulb should only light when A and B are closed, this is an AND gate. This circuit uses electrical versions of Boolean, XOR, and AND operators.

And it is possible to build other Boolean operators as electronic gates for things like OR, NOR, and NAND. And you might say, what's the problem? I mean, the problem is that you just tricked a bunch of electrons into doing the math for you. Sure, it's very simple math, but you could connect several of these half-adders and build increasingly complicated circuits that could perform more complex math, which is exactly what Stibitz and his colleagues did at Bell Labs. Two years later, they built the model I, which had more than 400 relays and could add two eight-digit numbers in a tenth of a second.

It could also multiply eight-digit numbers and multiply complex numbers, although these more complicated operations took longer, about a minute per calculation. - So you put voltage across a coil and it will turn that switch on or off. So you have your two operands here. And if you want to add two numbers, then 2 is this, 3 is this, right? So 1, 0 is 2. - Yes. - And 1, 1 is 3. And then when you want to calculate it, you just press the Go button down here. We get 101. - I love the sound of that. This is incredible. - It's magic, so if you want to do something like, say, 8 more, that would be 4, so 8 + 8, I think, right? - Well. - Yes, 8 + 8, that would be, 16, no, it erases itself. - Well. - There you go.

Eight plus eight is 16 in binary, which would be 1 0 0 0 0. (machine click) This is essentially a 1-bit arithmetic unit. There are no logical functions. Just add. Now, let's say we want to do 5 - 2, the answer will be 3. So we turn on this little switch here that lets me know that I'm doing a subtraction operation and we subtract by doing the 2's complement. Basically, what we're doing is reversing one of the operands and add one. Now when I run it (the machine makes noise) we can see that 5 - 2 equals 3, so 2 and 1 are 3. Now, because of the way we do this, the final carry flag ends up lighting up here in the end.

But if we know that we are doing a subtraction operation, we know that this final carry flag will never be set otherwise. - Over the next 10 years, they built six more relay-based

computers

that were used by the US military and the National Advisory Committee for Astronautics or NACA, which later became NASA. But even by the early 1940s, it was clear that the mechanical nature of the relay, the physical closing and opening of switches, was too slow to be the future of computers and they were also prone to failure. - Any time you have something mechanical, it will wear out.

Every time that relay switches, there is a little bit of friction at the point of rotation inside and there are contacts that make and break electrical connections, and they will wear out. - And all the relays opening and closing meant the computers were incredibly loud. (The machine makes noise) - So it doesn't really work very well in a business environment. You can't really put it in your office that you're going to drive people crazy. - So what computer scientists really needed was an electronic switch and that's where the vacuum tube triode comes into play. Oh! I mean, sure it can work as an amplifier if you put slightly positive or negative voltages into the network, but it can also work as a switch.

If the network voltage is very negative, no current flows. And if the grid voltage is very positive, then maximum current flows. Therefore, a triode can be controlled without moving parts. Only one voltage will set it to 0 or 1. And best of all, switching between the two can be done quickly and noiselessly, since you're only controlling electrons moving in a vacuum. This is the inventionthat took computing to the next level. The world's first programmable electronic computer was called ENIAC and first went into operation on December 10, 1945. It took up an entire room, weighed 30 tons, and consumed 175 kilowatts of power.

So much so that it generated a rumor that every time it was turned on, the lights of Philadelphia, where ENIAC was located, dimmed. Now, that was just a rumor, but mainly because ENIAC had its own dedicated electrical generator to keep up with the huge power consumption. Unlike previous computers, ENIAC was not limited to solving a single type of mathematical problem. It could be programmed and was fast, completing 500 operations per second. At that time, the word computers still referred to people who did calculations with pencil and paper. So 500 operations per second was really fast. The flexibility and power of ENIAC were immediately useful for the development of the hydrogen bomb.

The necessary calculations were so complex that the director of Los Alamos at the time said that "it would have been impossible to arrive at any solution without the help of ENIAC." - This is a fun part of having a processor that is 1 meter high and 70 centimeters wide, and that is that you can point out actual parts of the processor. - This is what a 1-bit vacuum tube computer looks like. - Can you feel the heat it gives off? - I certainly can. - I can feel the heat going away. - It's hot. - Well, I mean, 190 vacuum tubes is a lot.

I think we figured it out. This consumes like 350 or 400 watts of power or something, which is absurd. At night it is impressive. It looks like a city. - But there were also major failures in the vacuum tubes. The filaments always needed to be heated, so they consumed a lot of energy even when idle, and they were large. It was difficult to make a glass vacuum tube with complex, arbitrarily small electrodes inside. They were not reliable either. On average, a vacuum tube at ENIAC broke down every few days. And then it had to be found and replaced.

The longest ENIAC operated without failure was only 116 hours. The first digital computers were powered by glorified light bulbs. That's why they were so big, power-hungry and unreliable. The miracle and what has

made

our modern life possible is that someone discovered how to perform the same trick with electrons inside a solid piece of material, in silicon. But that's a story for another day. If you want to learn how modern computing devices store and access information, I recommend checking out the sponsor of this video, shiny.org. They have courses on everything from computer science fundamentals to neural networks and quantum computing.

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