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As the pioneers of computer science explored how to design a thinking machine, they realized

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that it had to perform four different tasks.

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It would need to take input, store information, process it, and then output the results.

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Now this might sound simple, but these four things are common to all computers.

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That's what makes a computer a computer.

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The earliest computers were made out of wood and metal, with mechanical levers and gears.

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By the 20th century, though, computers started using electrical components.

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These early computers were really large and really slow.

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A computer the size of a room might take hours just to do a basic math problem.

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These machines are things of gleaming, very colored metal, and numerous flashing lights.

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Computers started out as basic calculators, which was already really awesome at the time,

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and they were only manipulating numbers back then.

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But now we can use them to talk to each other, we can use them to play games, control robots,

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and do any crazy thing that you could probably imagine.

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Modern computers look nothing like those clunky old machines, but they still do these same

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four things.

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Next we're going to talk about input.

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This is my favorite, because what input is, is the stuff that the world does, or that

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you do, that makes the computer do stuff.

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You can tell a computer what to do with a keyboard, you can tell them what to do with

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a mouse, the microphone, the camera, and now if you're wearing a computer on your wrist,

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it might listen to your heartbeat, or in your car it might be listening to what the car

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is doing, and a touch screen can actually sense your finger and it takes that as input

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on what it's doing.

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All these different inputs give a computer information, which is then stored in memory.

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A computer's processor takes information from memory, it manipulates it, or changes it,

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using an algorithm, which is just a series of commands, and then it sends the processed

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information back to be stored in memory again.

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This continues until the processed information is ready to be output.

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How a computer outputs information depends on what the computer is designed to do.

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A computer display can show text, photos, videos, or interactive games, even virtual

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reality.

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The output of a computer may even include signals to control a robot.

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And when computers connect over the internet, the output from one computer becomes the input

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to another, and vice versa.

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You may have heard that computers work on ones and zeros, or you may have seen scary

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looking visuals like this, but almost nobody today actually deals directly with these ones

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and zeros.

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But ones and zeros do play a big role in how computers work on the inside.

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Inside a computer are electric wires and circuits that carry all the information in a computer.

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How do you store or represent information using electricity?

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Well, if you have a single wire with electricity flowing through it, the signal can either

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be on or off.

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That's not a lot of choices, but it's a really important start.

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With one wire, we can represent a yes or a no, true or false, a one or a zero, or anything

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else with only two options.

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This on-off state of a single wire is called a bit, and it's the smallest piece of information

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a computer can store.

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If you use more wires, you get more bits.

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More ones and zeros, with more bits, you can represent more complex information.

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But to understand that, we need to learn about something called the binary number system.

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In the decimal number system, we have 10 digits from 0 to 9, and that's how we've all learned

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to count.

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In the binary number system, we only have two digits, 0 and 1.

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With these two digits, we can count up to any number.

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Here's how this works.

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In the decimal number system we're all used to, each position in a number has a different

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value.

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There's the 1 position, the 10 position, the 100 position, and so on.

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For example, a 9 in the 100 position is a 900.

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In binary, each position also carries a value, but instead of multiplying by 10 each time,

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we multiply by 2.

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So there's the 1s position, the 2s position, the 4s position, the 8s position, and so on.

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For example, the number 9 in binary is 1001.

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To calculate the value, we add 1 times 8 plus 0 times 4 plus 0 times 2 plus 1 times 1.

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Almost nobody does this math because computers do it for us.

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What's important is that any number can be represented with only 1s and 0s, or by a bunch

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of wires that are on or off.

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The more wires you use, the larger the numbers you can store.

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With 8 wires, you can store numbers between 0 and 255, that's 8 1s.

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With just 32 wires, you can store all the way from 0 to over 4 billion.

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Using the binary number system, you can represent any number you like.

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But what about other types of information, like text, images, or sound?

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It turns out that all these things can also be represented with numbers.

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Think of all the letters in the alphabet.

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You could assign a number to each letter, A could be 1, B could be 2, and so on.

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You can then represent any word or paragraph as a sequence of numbers.

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And as we saw, these numbers can be stored as on or off electrical signals.

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Every word you see on every webpage or your phone is represented using a system like this.

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Now let's consider photos, videos, and all the graphics you see on a screen.

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All of these images are made out of teeny dots called pixels, and each pixel has a color.

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Each of the colors can be represented with numbers.

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When you consider that a typical image has millions of these pixels, and a typical video

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shows 30 images per second, now we're talking about a lot of data here.

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Every sound is basically a series of vibrations in the air.

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Vibrations can be represented graphically as a waveform.

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Any point on this waveform can be represented by a number.

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In this way, any sound can be broken down into a series of numbers.

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If you want higher quality sound, you would pick 32-bit audio over 8-bit audio.

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More bits means a higher range of numbers.

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When you use a computer to write code or make your own app, you're not dealing directly

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with these ones and zeros, but you will be dealing with images, or sound, or video.

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So if you want to understand how computers work on the inside, it all comes down to these

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simple ones and zeros, and the electrical signals in the circuits behind them.

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They are the backbone of how all computers input, store, process, and output information.

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Under the hood, all computers do the same four basic things.

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They input information, store and process the information, and then output information.

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Each of these things is done by a different part of the computer.

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There are input devices that take input from the outside world and convert it into binary

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information.

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There is memory to store this information.

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There is a central processing unit, or CPU, where all the calculations are done.

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And finally, there are output devices that take information and convert it into physical

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output.

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Let's talk about input first.

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Computers can take many different types of input, like the keyboard of a computer, the

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touchpad of a phone, a camera, a microphone, or a GPS.

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But even the sensors on a car, a thermostat, or a drone are also different input devices.

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Now let's look at a simple example of how input travels through a computer and becomes

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output.

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When you press a key on your keyboard, let's say the letter B, the keyboard converts the

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letter to a number.

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That number is sent as binary, ones and zeros, into the computer.

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Starting from this number, the CPU calculates how to display the letter B pixel by pixel.

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The CPU requests step-by-step instructions from memory, which tell it how to draw the

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letter B. The CPU runs these instructions and stores the results as pixels in memory.

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Finally, this pixel information is sent in binary to the screen.

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The screen is an output device, which converts the binary signals into the tiny lights and

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colors that make up what you see.

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This all happens so quickly it feels instantaneous.

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But to display each letter, a computer runs thousands of instructions, starting from the

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moment your finger presses the keyboard.

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In that example, the output device was the screen.

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But there are many different types of output which take a binary signal from the computer

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and do something in the physical world.

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For example, a speaker will play sound, and a 3D printer will print an object.

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Output devices can also control physical motion, like a robotic arm, the motor of a car, or

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the cutting tool of the milling machine that my company makes.

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New types of inputs and outputs let computers interact with the world in entirely new ways.

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This has been helped out by improvements to the speed and size of the memory and CPU.

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The more complicated a task is, and the more information that's input or output, the more

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processing power and memory a computer needs.

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Typing letters on a screen may be easy, but to do complicated 3D graphics or record a

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high-definition movie, modern computers often have multiple CPUs to process all that information

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and many gigabytes of memory to store it.

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No matter what it is you want to do with a computer, every single action is about inputting

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information from the physical world, storing and processing that information, and getting

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some output back into the physical world.

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When you look inside a computing device, you see a bunch of circuits, chips, wires, speakers,

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plugs, and all sorts of other stuff.

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This is the hardware.

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But what you don't see is the software.

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Software is all of the computer programs, or code, running on this machine.

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Software can be anything from apps and games to webpages and the data science software

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that me and my teams use at Amazon to understand how customers behave.

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But how do the hardware and the software interact with one another?

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Let's start at looking at a computer's central processing unit, or CPU.

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The CPU is the master chip that controls all the other parts of the computer.

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A CPU needs to do different things, so inside it has smaller, simpler parts that handle

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specific tasks.

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It has circuits to do simple math and logic.

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It has other circuits to send and receive information to and from different parts of

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the computer.

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The real magic of the CPU is how it knows which circuits to use and when to use them.

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The CPU receives simple commands that tell it which circuit to use to do a specific job.

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For example, an add command tells the CPU to use its adder circuit to calculate a new

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number.

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And then the store command tells the CPU to use a different circuit to save that result

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into memory.

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Just like numbers, all of these simple commands can be represented in binary 1s and 0s, or

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on and off electrical signals.

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The binary commands are stored in memory, and the CPU fetches and executes them in sequence,

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one after the other.

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This sequence of commands is in fact a very simple computer program.

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Binary code is the most basic form of software, and it controls all the hardware of a computer.

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These days, nobody writes software in binary.

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It would take forever!

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Today, the software we write looks more like this, or this, or even this.

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Programming languages like these let you type in commands in something that looks a lot

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like English.

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To draw a rectangle on the screen, you just need a single command.

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This high-level command is converted into hundreds or thousands of simpler binary commands

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that the CPU understands.

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Software tells the CPU what to do.

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But when you're listening to music and browsing the web and chatting with a friend, your computer

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is running multiple pieces of software all at once.

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So how do all of these programs get on the computer in the first place?

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And how can the CPU run them all at once?

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To find out, we'll have to take a look at the operating system.

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The operating system of the computer is the master program that manages how software gets

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to use the hardware of the computer.

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For example, I helped create the Windows operating system that runs on most personal computers.

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The operating system is a program with special abilities that let it control the other software

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on the computer.

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It lets you install new programs by loading them into your computer's memory.

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It decides when a program is run by the central processing unit, and whether that program

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can access the computer's input and output devices.

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And when you think your computer is running many programs at once, in reality, it's the

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operating system that's quickly switching between programs, sharing that CPU for fractions

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of a second.

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Inside every computer is an operating system managing software that controls the computer's

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hardware.

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The software is a series of commands made of simple binary code.

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And that binary code is just electrical signals flowing through billions of tiny circuits.