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  • Hello world, I’m Carrie Anne, and welcome to CrashCourse Computer Science!

  • Over the course of this series, were going to go from bits, bytes, transistors and logic

  • gates, all the way to Operating Systems, Virtual Reality and Robots!

  • Were going to cover a lot, but just to clear things up - we ARE NOT going to teach

  • you how to program.

  • Instead, were going to explore a range of computing topics as a discipline and a

  • technology.

  • Computers are the lifeblood of today’s world.

  • If they were to suddenly turn off, all at once, the power grid would shut down, cars

  • would crash, planes would fall, water treatment plants would stop, stock markets would freeze,

  • trucks with food wouldn’t know where to deliver, and employees wouldn’t get paid.

  • Even many non-computer objects - like DFTBA shirts and the chair I’m sitting onare

  • made in factories run by computers.

  • Computing really has transformed nearly every aspect of our lives.

  • And this isn’t the first time weve seen this sort of technology-driven global change.

  • Advances in manufacturing during the Industrial Revolution brought a new scale to human civilization

  • - in agriculture, industry and domestic life.

  • Mechanization meant superior harvests and more food, mass produced goods, cheaper and

  • faster travel and communication, and usually a better quality of life.

  • And computing technology is doing the same right nowfrom automated farming and medical

  • equipment, to global telecommunications and educational opportunities, and new frontiers

  • like Virtual Reality and Self Driving Cars.

  • We are living in a time likely to be remembered as the Electronic Age.

  • With billions of transistors in just your smartphones, computers can seem pretty complicated,

  • but really, theyre just simple machines that perform complex actions through many

  • layers of abstraction.

  • So in this series, were going break down those layers, and build up from simple 1’s

  • and 0’s, to logic units, CPUs, operating systems, the entire internet and beyond.

  • And don’t worry, in the same way someone buying t-shirts on a webpage doesn’t need

  • to know how that webpage was programmed, or the web designer doesn’t need to know how

  • all the packets are routed, or router engineers don’t need to know about transistor logic,

  • this series will build on previous episodes but not be dependent on them.

  • By the end of this series, I hope that you can better contextualize computing’s role

  • both in your own life and society, and how humanity's (arguably) greatest invention is

  • just in its infancy, with its biggest impacts yet to come.

  • But before we get into all that, we should start at computing’s origins, because although

  • electronic computers are relatively new, the need for computation is not.

  • INTRO

  • The earliest recognized device for computing

  • was the abacus, invented in Mesopotamia around 2500 BCE.

  • It’s essentially a hand operated calculator, that helps add and subtract many numbers.

  • It also stores the current state of the computation, much like your hard drive does today.

  • The abacus was created because, the scale of society had become greater than what a

  • single person could keep and manipulate in their mind.

  • There might be thousands of people in a village or tens of thousands of cattle.

  • There are many variants of the abacus, but let’s look at a really basic version with

  • each row representing a different power of ten.

  • So each bead on the bottom row represents a single unit, in the next row they represent

  • 10, the row above 100, and so on.

  • Let’s say we have 3 heads of cattle represented by 3 beads on the bottom row on the right side.

  • If we were to buy 4 more cattle we would just slide 4 more beads to the right for a total of 7.

  • But if we were to add 5 more after the first 3 we would run out of beads, so we would slide

  • everything back to the left, slide one bead on the second row to the right, representing

  • ten, and then add the final 2 beads on the bottom row for a total of 12.

  • This is particularly useful with large numbers.

  • So if we were to add 1,251 we would just add 1 to the bottom row, 5 to the second row,

  • 2 to the third row, and 1 to the fourth row - we don’t have to add in our head and the

  • abacus stores the total for us.

  • Over the next 4000 years, humans developed all sorts of clever computing devices, like

  • the astrolabe, which enabled ships to calculate their latitude at sea.

  • Or the slide rule, for assisting with multiplication and division.

  • And there are literally hundred of types of clocks created that could be used to calculate

  • sunrise, tides, positions of celestial bodies, and even just the time.

  • Each one of these devices made something that was previously laborious to calculate much

  • faster, easier, and often more accurate –– it lowered the barrier to entry, and at the same

  • time, amplified our mental abilities –– take note, this is a theme were going to touch

  • on a lot in this series.

  • As early computer pioneer Charles Babbage said: “At each increase of knowledge, as

  • well as on the contrivance of every new tool, human labour becomes abridged.”

  • However, none of these devices were calledcomputers”.

  • The earliest documented use of the wordcomputeris from 1613, in a book by Richard Braithwait.

  • And it wasn’t a machine at all - it was a job title.

  • Braithwait said, “I have read the truest computer of times,

  • and the best arithmetician that ever breathed, and he reduceth thy dayes into a short number”.

  • In those days, computer was a person who did calculations, sometimes with the help of machines,

  • but often not.

  • This job title persisted until the late 1800s, when the meaning of computer started shifting

  • to refer to devices.

  • Notable among these devices was the Step Reckoner, built by German polymath Gottfried Leibniz

  • in 1694.

  • Leibniz said “... it is beneath the dignity of excellent men to waste their time in calculation

  • when any peasant could do the work just as accurately with the aid of a machine.”

  • It worked kind of like the odometer in your car, which is really just a machine for adding

  • up the number of miles your car has driven.

  • The device had a series of gears that turned; each gear had ten teeth, to represent the

  • digits from 0 to 9.

  • Whenever a gear bypassed nine, it rotated back to 0 and advanced the adjacent gear by one tooth.

  • Kind of like when hitting 10 on that basic abacus.

  • This worked in reverse when doing subtraction, too.

  • With some clever mechanical tricks, the Step Reckoner was also able to multiply and divide

  • numbers.

  • Multiplications and divisions are really just many additions and subtractions.

  • For example, if we want to divide 17 by 5, we just subtract 5, then 5, then 5 again,

  • and then we can’t subtract any more 5’s… so we know 5 goes into 17 three times, with

  • 2 left over.

  • The Step Reckoner was able to do this in an automated way, and was the first machine that

  • could do all four of these operations.

  • And this design was so successful it was used for the next three centuries of calculator design.

  • Unfortunately, even with mechanical calculators, most real world problems required many steps

  • of computation before an answer was determined.

  • It could take hours or days to generate a single result.

  • Also, these hand-crafted machines were expensive, and not accessible to most of the population.

  • So, before 20th century, most people experienced computing through pre-computed tables assembled

  • by those amazinghuman computerswe talked about.

  • So if you needed to know the square root of 8 million 6 hundred and 75 thousand 3 hundred

  • and 9, instead of spending all day hand-cranking your step reckoner, you could look it up in

  • a huge book full of square root tables in a minute or so.

  • Speed and accuracy is particularly important on the battlefield, and so militaries were

  • among the first to apply computing to complex problems.

  • A particularly difficult problem is accurately firing artillery shells, which by the 1800s

  • could travel well over a kilometer (or a bit more than half a mile).

  • Add to this varying wind conditions, temperature, and atmospheric pressure, and even hitting

  • something as large as a ship was difficult.

  • Range Tables were created that allowed gunners to look up environmental conditions and the

  • distance they wanted to fire, and the table would tell them the angle to set the canon.

  • These Range Tables worked so well, they were used well into World War Two.

  • The problem was, if you changed the design of the cannon or of the shell, a whole new

  • table had to be computed, which was massively time consuming and inevitably led to errors.

  • Charles Babbage acknowledged this problem in 1822 in a paper to the Royal Astronomical

  • Society entitled: “Note on the application of machinery to the computation of astronomical

  • and mathematical tables".

  • Let’s go to the thought bubble.

  • Charles Babbage proposed a new mechanical device called the Difference Engine, a much

  • more complex machine that could approximate polynomials.

  • Polynomials describe the relationship between several variables - like range and air pressure,

  • or amount of pizza Carrie Anne eats and happiness.

  • Polynomials could also be used to approximate logarithmic and trigonometric functions, which

  • are a real hassle to calculate by hand.

  • Babbage started construction in 1823, and over the next two decades, tried to fabricate

  • and assemble the 25,000 components, collectively weighing around 15 tons.

  • Unfortunately, the project was ultimately abandoned.

  • But, in 1991, historians finished constructing a Difference Engine based on Babbage's drawings

  • and writings - and it worked!

  • But more importantly, during construction of the Difference Engine, Babbage imagined

  • an even more complex machine - the Analytical Engine.

  • Unlike the Difference Engine, Step Reckoner and all other computational devices before

  • it - the Analytical Engine was a “general purpose computer”.

  • It could be used for many things, not just one particular computation; it could be given

  • data and run operations in sequence; it had memory and even a primitive printer.

  • Like the Difference Engine, it was ahead of its time, and was never fully constructed.

  • However, the idea of anautomatic computer” – one that could guide itself through a

  • series of operations automatically, was a huge deal, and would foreshadow computer programs.

  • English mathematician Ada Lovelace wrote hypothetical programs for the Analytical Engine, saying,

  • “A new, a vast, and a powerful language is developed for the future use of analysis.”

  • For her work, Ada is often considered the world’s first programmer.

  • The Analytical Engine would inspire, arguably, the first generation of computer scientists,

  • who incorporated many of Babbage’s ideas in their machines.

  • This is why Babbage is often considered the "father of computing".

  • Thanks Thought Bubble!

  • So by the end of the 19th century, computing devices were used for special purpose tasks

  • in the sciences and engineering, but rarely seen in business, government or domestic life.

  • However, the US government faced a serious problem for its 1890 census that demanded

  • the kind of efficiency that only computers could provide.

  • The US Constitution requires that a census be conducted every ten years, for the purposes

  • of distributing federal funds, representation in congress, and good stuff like that.

  • And by 1880, the US population was booming, mostly due to immigration.

  • That census took seven years to manually compile and by the time it was completed, it was already

  • out of dateand it was predicted that the 1890 census would take 13 years to compute.

  • That’s a little problematic when it’s required every decade!

  • The Census bureau turned to Herman Hollerith, who had built a tabulating machine.

  • His machine waselectro-mechanical” – it used traditional mechanical systems for keeping

  • count, like Leibniz’s Step Reckoner –– but coupled them with electrically-powered components.

  • Hollerith’s machine used punch cards which were paper cards with a grid of locations

  • that can be punched out to represent data.

  • For example, there was a series of holes for marital status.

  • If you were married, you would punch out the married spot, then when the card was inserted

  • into Hollerith’s machine, little metal pins would come down over the cardif a spot

  • was punched out, the pin would pass through the hole in the paper and into a little vial

  • of mercury, which completed the circuit.

  • This now completed circuit powered an electric motor, which turned a gear to add one, in

  • this case, to themarriedtotal.

  • Hollerith’s machine was roughly 10x faster than manual tabulations, and the Census was

  • completed in just two and a half years - saving the census office millions of dollars.

  • Businesses began recognizing the value of computing, and saw its potential to boost

  • profits by improving labor- and data-intensive tasks, like accounting, insurance appraisals,

  • and inventory management.

  • To meet this demand, Hollerith founded The Tabulating Machine Company, which later merged

  • with other machine makers in 1924 to become The International Business Machines Corporation

  • or IBM - which youve probably heard of.

  • These electro-mechanicalbusiness machineswere a huge success, transforming commerce

  • and government, and by the mid-1900s, the explosion in world population and the rise

  • of globalized trade demanded even faster and more flexible tools for processing data, setting

  • the stage for digital computers, which well talk about next week.

Hello world, I’m Carrie Anne, and welcome to CrashCourse Computer Science!

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早期計算。計算機科學速成班 #1 (Early Computing: Crash Course Computer Science #1)

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    黃齡萱 發佈於 2021 年 01 月 14 日
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