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  • Our last episode brought us to the start of the 20th century, where early, special purpose

  • computing devices, like tabulating machines, were a huge boon to governments and business

  • - aiding, and sometimes replacing, rote manual tasks. But the scale of human systems continued

  • to increase at an unprecedented rate. The first half of the 20th century saw the

  • world’s population almost double. World War 1 mobilized 70 million people, and World

  • War 2 involved more than 100 million. Global trade and transit networks became interconnected

  • like never before, and the sophistication of our engineering and scientific endeavors

  • reached new heightswe even started to seriously consider visiting other planets.

  • And it was this explosion of complexity, bureaucracy, and ultimately data, that drove an increasing

  • need for automation and computation. Soon those cabinet-sized electro-mechanical

  • computers grew into room-sized behemoths that were expensive to maintain and prone to errors.

  • And it was these machines that would set the stage for future innovation.

  • INTRO

  • One of the largest electro-mechanical computers

  • built was the Harvard Mark I, completed in 1944 by IBM for the Allies during World War 2.

  • It contained 765,000 components, three million connections, and five hundred miles of wire.

  • To keep its internal mechanics synchronized,

  • it used a 50-foot shaft running right through the machine driven by a five horsepower motor.

  • One of the earliest uses for this technology was running simulations for the Manhattan Project.

  • The brains of these huge electro-mechanical

  • beasts were relays: electrically-controlled mechanical switches. In a relay, there is

  • a control wire that determines whether a circuit is opened or closed. The control wire connects

  • to a coil of wire inside the relay. When current flows through the coil, an electromagnetic

  • field is created, which in turn, attracts a metal arm inside the relay, snapping it

  • shut and completing the circuit. You can think of a relay like a water faucet. The control

  • wire is like the faucet handle. Open the faucet, and water flows through the pipe. Close the

  • faucet, and the flow of water stops.

  • Relays are doing the same thing, just with

  • electrons instead of water. The controlled circuit can then connect to other circuits,

  • or to something like a motor, which might increment a count on a gear, like in Hollerith's

  • tabulating machine we talked about last episode. Unfortunately, the mechanical arm inside of

  • a relay *has mass*, and therefore can’t move instantly between opened and closed states.

  • A good relay in the 1940’s might be able to flick back and forth fifty times in a second.

  • That might seem pretty fast, but it’s not fast enough to be useful at solving large,

  • complex problems. The Harvard Mark I could do 3 additions or

  • subtractions per second; multiplications took 6 seconds, and divisions took 15.

  • And more complex operations, like a trigonometric function, could take over a minute.

  • In addition to slow switching speed, another limitation was wear and tear. Anything mechanical

  • that moves will wear over time. Some things break entirely, and other things start getting

  • sticky, slow, and just plain unreliable.

  • And as the number of relays increases, the

  • probability of a failure increases too. The Harvard Mark I had roughly 3500 relays. Even

  • if you assume a relay has an operational life of 10 years, this would mean you’d have

  • to replace, on average, one faulty relay every day! That’s a big problem when you are in

  • the middle of running some important, multi-day calculation.

  • And that’s not all engineers had to contend with. These huge, dark, and warm machines

  • also attracted insects. In September 1947, operators on the Harvard Mark II pulled a

  • dead moth from a malfunctioning relay. Grace Hopper who well talk more about in a later episode noted,

  • From then on, when anything went wrong with a computer,

  • we said it had bugs in it.”

  • And that’s where we get the term computer bug.

  • It was clear that a faster, more reliable alternative to electro-mechanical relays was

  • needed if computing was going to advance further, and fortunately that alternative already existed!

  • In 1904, English physicist John Ambrose Fleming developed a new electrical component called

  • a thermionic valve, which housed two electrodes inside an airtight glass bulb - this was the

  • first vacuum tube. One of the electrodes could be heated, which would cause it to emit electrons

  • – a process called thermionic emission. The other electrode could then attract these

  • electrons to create the flow of our electric faucet, but only if it was positively charged

  • - if it had a negative or neutral charge, the electrons would no longer be attracted

  • across the vacuum so no current would flow.

  • An electronic component that permits the one-way

  • flow of current is called a diode, but what was really needed was a switch to help turn

  • this flow on and off. Luckily, shortly after, in 1906, American inventor Lee de Forest added

  • a thirdcontrolelectrode that sits between the two electrodes in Fleming’s design.

  • By applying a positive charge to the control electrode, it would permit the flow

  • of electrons as before. But if the control electrode was given a negative charge, it

  • would prevent the flow of electrons. So by manipulating the control wire, one could

  • open or close the circuit. It’s pretty much the same thing as a relay - but importantly,

  • vacuum tubes have no moving parts. This meant there was less wear, and more importantly,

  • they could switch thousands of times per second. These triode vacuum tubes would become the

  • basis of radio, long distance telephone, and many other electronic devices for nearly a

  • half century. I should note here that vacuum tubes weren’t perfect - theyre kind of

  • fragile, and can burn out like light bulbs, they were a big improvement over mechanical relays.

  • Also, initially vacuum tubes were expensive

  • – a radio set often used just one, but a computer might require hundreds or thousands of electrical switches.

  • But by the 1940s, their cost and reliability had improved to

  • the point where they became feasible for use in computers…. at least by people with deep

  • pockets, like governments. This marked the shift from electro-mechanical

  • computing to electronic computing. Let’s go to the Thought Bubble.

  • The first large-scale use of vacuum tubes for computing was the Colossus Mk 1 designed

  • by engineer Tommy Flowers and completed in December of 1943. The Colossus was installed

  • at Bletchley Park, in the UK, and helped to decrypt Nazi communications.

  • This may sound familiar because two years prior Alan Turing, often called the father

  • of computer science, had created an electromechanical device, also at Bletchley Park, called the

  • Bombe. It was an electromechanical machine designed to break Nazi Enigma codes, but the

  • Bombe wasn’t technically a computer, and well get to Alan Turing’s contributions

  • later. Anyway, the first version of Colossus contained

  • 1,600 vacuum tubes, and in total, ten Colossi were built to help with code-breaking.

  • Colossus is regarded as the first programmable, electronic computer.

  • Programming was done by plugging hundreds of wires into plugboards, sort of like old

  • school telephone switchboards, in order to set up the computer to perform the right operations.

  • So whileprogrammable”, it still had to be configured to perform a specific computation.

  • Enter the The Electronic Numerical Integrator and Calculatoror ENIACcompleted

  • a few years later in 1946 at the University of Pennsylvania.

  • Designed by John Mauchly and J. Presper Eckert, this was the world's first truly general purpose,

  • programmable, electronic computer.

  • ENIAC could perform 5000 ten-digit additions or subtractions per second, many, many times

  • faster than any machine that came before it. It was operational for ten years, and is estimated

  • to have done more arithmetic than the entire human race up to that point.

  • But with that many vacuum tubes failures were common, and ENIAC was generally only operational

  • for about half a day at a time before breaking down.

  • Thanks Thought Bubble. By the 1950’s, even vacuum-tube-based computing was reaching its limits.

  • The US Air Force’s AN/FSQ-7 computer, which was completed in 1955, was part of the

  • SAGEair defense computer system well talk more about in a later episode.

  • To reduce cost and size, as well as improve reliability and speed, a radical new electronic

  • switch would be needed. In 1947, Bell Laboratory scientists John Bardeen, Walter Brattain,

  • and William Shockley invented the transistor, and with it, a whole new era of computing was born!

  • The physics behind transistors is pretty complex, relying on quantum mechanics,

  • so were going to stick to the basics.

  • A transistor is just like a relay or vacuum tube - it’s a switch that can be opened

  • or closed by applying electrical power via a control wire. Typically, transistors have

  • two electrodes separated by a material that sometimes can conduct electricity, and other

  • times resist it – a semiconductor. In this case, the control wire attaches to

  • a “gateelectrode. By changing the electrical charge of the gate, the conductivity of the

  • semiconducting material can be manipulated, allowing current to flow or be stoppedlike

  • the water faucet analogy we discussed earlier. Even the very first transistor at Bell Labs

  • showed tremendous promiseit could switch between on and off states 10,000 times per second.

  • Further, unlike vacuum tubes made of glass and with carefully suspended, fragile

  • components, transistors were solid material known as a solid state component.

  • Almost immediately, transistors could be made smaller than the smallest possible relays or vacuum tubes.

  • This led to dramatically smaller and cheaper computers, like the IBM 608, released in 1957

  • the first fully transistor-powered, commercially-available computer.

  • It contained 3000 transistors and could perform 4,500 additions, or roughly

  • 80 multiplications or divisions, every second. IBM soon transitioned all of its computing

  • products to transistors, bringing transistor-based computers into offices, and eventually, homes.

  • Today, computers use transistors that are smaller than 50 nanometers in sizefor

  • reference, a sheet of paper is roughly 100,000 nanometers thick. And theyre not only incredibly

  • small, theyre super fastthey can switch states millions of times per second, and can run for decades.

  • A lot of this transistor and semiconductor development happened in the Santa Clara Valley,

  • between San Francisco and San Jose, California.

  • As the most common material used to create semiconductors is silicon, this

  • region soon became known as Silicon Valley. Even William Shockley moved there, founding

  • Shockley Semiconductor, whose employees later founded

  • Fairchild Semiconductors, whose employees later founded

  • Intel - the world’s largest computer chip maker today.

  • Ok, so weve gone from relays to vacuum tubes to transistors. We can turn electricity

  • on and off really, really, really fast. But how do we get from transistors to actually

  • computing something, especially if we don’t have motors and gears?

  • That’s what were going to cover over the next few episodes.

  • Thanks for watching. See you next week.

Our last episode brought us to the start of the 20th century, where early, special purpose

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電子計算機。クラッシュコース コンピュータサイエンス #2 (Electronic Computing: Crash Course Computer Science #2)

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    黃齡萱 に公開 2021 年 01 月 14 日
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