مقدمة في علوم الكمبيوتر: من العداد إلى الحواسيب الحديثة

[Music] hello world I'm kianne and welcome to crash course computer science over the

course of this series we're going to go from bits bites transistors and logic gates all the way to operating systems

virtual reality and robots we're going to cover a lot but just to clear things up we are not going to teach you how to

program instead we're 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 PL 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 on are made in factories run by computers Computing really has transformed nearly every

aspect of our lives and this isn't the first time we've seen this sort of technology-driven global change advances

in manufacturing during the Industrial Revolution brought 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 now from

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 and with billions of transistors in just your smartphones computers can seem pretty complicated

but really they're just simple machines that perform complex actions through many layers of abstraction so in this

series we're going to break down those layers and build up from simple ones and zeros 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 web page doesn't

need to know how that web page was programmed or the web designer doesn't need to know how all the packets are

rooted or rter 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

impact 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 [Music]

not the earliest recognized device for computing was the Abacus invented in Mesopotamia around 2,500 BC 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 10 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 three heads of cattle represented by three beads on

the bottom row on the right side if we were to buy four more cattle we would just slide four more beads to the right

for a total of seven but if we were to add five more after the first three 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 10 and then add the final

two beads on the bottom row for a total 12 this is particularly useful with large numbers so if we were to add

1,251 we would just add one to the bottom row five to the second row two to the third row and one to the fourth row

we don't have to add in our head and the Abacus stores the total for us over the next 4,000 years humans developed all

sorts of clever Computing devices like the astrolab which enabled ships to calculate their latitude at CA or the

slide rule for assisting with multiplication and division and there are literally hundreds 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 we're 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 labor becomes Abridged however none of these devices

were called computers the earliest documented use of the word computer is from 1613 in a book by Richard braithway

and it wasn't a machine at all it was a job title braith weight said I have read the truest computer of times and the

best arithmetician that ever breathed and he reduth th days 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 computers started shifting to refer to devices and notable among these devices was the step

reckoner built by German polymath godfried leitz in 1694 liit 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

is driven the device had a series of Gears that turned each gear had 10 teeth to represent the digits from 0 to 9

whenever a gear bypast N9 it rotated back to zero and advanced the adjacent gear by one to kind of like when hitting

on that basic Abacus this worked in Reverse when doing subtraction to 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 five then five then five again and then we

can't subtract any more fives so we know five goes into 17 three times with two left over the St reer 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 handcrafted machines were expensive and not accessible to

most of the population before the 20th century most people experienced Computing through pre-computed tables

assembled by those amazing human computers we talked about so if you needed to know the square root of

8,675 5,39 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 cannon these range

tables worked so well they were used well into World War II the problem was if you change the design of the cannon

or of the shell a whole new table had to be computed which was massively timec 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 polinomial pols describe the relationship between several variables

like range and air pressure or amount of pizza caran eats and happiness polinomial could also be used to

approximate logarithmic and trigonometric function 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 babage imagined an even more complex machine the analytical

engine unlike the Difference Engine St reer 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 off 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 an automatic computer one that could guide

itself through a series of operations automatically was a huge deal and would foreshadow computer programs English

mathematician aah 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 adah is often considered the world's first

programmer the analytical engine would go on to inspire arguably the first generation of computer scientists who

Incorporated many of babbage's ideas in their machines this is why babage is often considered the father of computing

thanks for 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 1819 census that demanded the kind of efficiency that only computers could provide the US

Constitution requires that a census be conducted every 10 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 7 years to manually compile and by the time it was completed it was already out of date and

it was predicted that the 1819 census would take 13 years to compute that's a little problematic when it's required

every decade the Census Bureau turned to Herman holth who built a tabulating machine his machine was

electromechanical he used traditional mechanical systems for keeping count like Le his step reckoner but coupled

them with electrically powered components poist machine used Punch Cards which were paper cards with a grid

of locations that could 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 hollus machine little

metal pins would come down over the card if a spot was punched out the pin would pass through the hole in the paper and

into a little VI of mercury which completed the circuit this now completed circuit powered an electric motor which

turned a gear to to add one in this case to the married total hollist machine was roughly 10 times 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 holler

founded the tabulating machine company which later merged with other machine makers in 1924 to become the

International Business Machines Corporation or IBM which you've probably heard of these electromechanical

Business Machines were 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 we'll talk about next week crash course computer science is produced in

association with PBS digital Studios at their Channel you can check out a playlist of shows like PBS idea channnel

physics girl and it's okay to be smart this episode was filmed at the Chad and Stacy igol studio in Indianapolis

Indiana and it was made with the help of all these nice people and our wonderful Graphics team thought Cafe thanks for

watching I'll see you later [Music]