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Input & output devices

As computer users, we're the most familiar with the parts of the computer that we interact with daily: the input and output devices.


The very first computers only accepted "punch cards" as input. Computer scientists had to carefully punch out their instructions and then feed the cards into the computer.
A piece of card stock with numbers printed in rows and columns, with some numbers punched out.
A punch card used in the 1970s to input Fortran programs into an IBM mainframe computer. Source: Harke, Wikipedia
Fortunately, computers have come a long way since the 1970s, and we can now input data into them using a variety of easy-to-use devices. The most common input devices are the keyboard, mouse, and touch screen.
Portable keyboard, wireless mouse, and iPhone.
There are hundreds of other input devices, like microphones to capture sound waves, scanners to capture image data, and virtual reality devices to capture our body movements.
Computers also receive input from their environment using "sensors", like motion sensors that detect changes in movement.
🤔What other input devices have you used? What new input devices will we have 20 years from now?


Once the CPU is done processing the data, it often needs to output a result.
A standard output device is the computer monitor, which displays text, images, and user interface elements by lighting up thousands of pixels with different colors.
A computer monitor with a calculator program displayed. The calculator shows that 2 + 2 = 4.
There are many other ways a computer could output data. As long as the output device can interpret a stream of 1s and 0s, it can turn that data into anything - headphones output sound, printers output ink on paper, and projectors output light.

Exploring inputs and outputs

Discover more types of inputs and outputs in the upcoming exercises.
🔍 If you've never heard of a device before, just search for more information online.
Classroom Computer Inputs/Outputs
A teacher is coming up with a wishlist for computer accessories for their classroom.
Identify whether each accessory is a computer "input" or "output":
AccessoryInput or output?
3D printer
digital stylus
laser cutter
USB guitar cable

Arduino Inputs/Outputs
A gardener is setting up an Arduino computer to monitor the health of their garden, using a combination of input and output devices.
Identify whether each device is a computer "input" or "output":
DeviceInput or output?
LED (Light emitting diode)
temperature sensor
pH sensor
moisture sensor
16x2 LCD (Liquid crystal display)

E-Textile Inputs/outputs
A fashion designer is working on an e-textile project, a jacket that will light up according to their biometrics and the environment. They're using a Lilypad Arduino computer, plus a variety of input and output devices.
Identify whether each device is a computer "input" or "output":
DeviceInput or output?
muscle sensor
flex sensor
32x32 LED matrix
push button
LED ribbon

Home Security Inputs/Outputs
A home owner is setting up a home security system and is making a list of the hardware he'll need to buy.
Identify whether each hardware accessory is a computer "input" or "output":
AccessoryInput or output?
video camera
flat-screen monitor
audible alarm
motion sensor

🤔 Can you think of other output devices? What's a new output device that you could invent?

🙋🏽🙋🏻‍♀️🙋🏿‍♂️Do you have any questions about this topic? We'd love to answer— just ask in the questions area below!

Want to join the conversation?

  • primosaur sapling style avatar for user HTML Studios
    How exactly does the computer know which ones and zeros stand for different things? For example, if you type the letter B, how does it distinguish it from a different type of input?
    (12 votes)
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  • leaf green style avatar for user Zain
    What is an Arduino computer which is mentioned in above exercise?
    (4 votes)
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  • blobby green style avatar for user LiuYecheng
    I think the 3 d printer should be input and output, this right?
    (2 votes)
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    • starky seedling style avatar for user lmn32
      You could say that, but I would rather think of it as an output device. The thing is if it's also an input device, what's it outputting to 🤔? I wouldn't think of a printed plastic model as another computer, which makes it hard to think of the plastic as another thing capable of "inputting" a stream of 1's and 0's that tell a printer to print stuff.
      (2 votes)
  • winston default style avatar for user F H
    Is a radar input or output or both?
    (2 votes)
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    • duskpin ultimate style avatar for user Emma
      A radar is a system that contains both input and output portions. When the radar receives the signal that it is being turned on, it begins to take in information through the measuring of the radio waves it sends out. This is the output portion. When it sends the information back to wherever it is told to go, it is now an output.
      (2 votes)
  • leaf grey style avatar for user Quinn Hardbrook
    At my house, I have a small color sensor for a lego toy. When I turn it on, it emits a beam of light and reads what the color is that it’s above. I’m trying to figure out if it’s an input or output device.

    1. It has an on switch - input
    2. It emits a light beam - output
    3. It reads colors - input
    4. It tells what color it’s reading - output

    It looks to me as if it’s a combination of the two. Are instruments such as this better categorized as their own computer as they have input and output?
    (0 votes)
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    • orange juice squid orange style avatar for user Evan
      This is a really great question! You're right that it has both input and output qualities. Although when determining if something is mainly an input or output device, it's best to think of it in relation to a computer. If the device's main purpose is to gather information for the computer, then it's an input device. If its main purpose is to let the computer communicate information to the user, then it's an output device.

      Although the color sensor has some input qualities and some output qualities, I would say its main function is to read colors. The other features are there just to help it with its main function (reading colors). So I would say that it's an input device. You could also count it as its own computer, with its own inputs and outputs, but typically that's not how it's categorized.

      Hope this made sense! (:
      (6 votes)
  • mr pink orange style avatar for user MR.PINK
    How does the computer know what its doing and does it make any mistakes.
    (2 votes)
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    • starky seedling style avatar for user lmn32
      It's a machine. Engineers want computers to act mechanically, so they use a lot of math and logic when organizing a computer system! this in turn gives the computer a lot of structure, which also serves to clarify its functionality! You have to admit that it's hard to make mistakes, when you're thinking is clear, and your work is neat!
      (1 vote)
  • blobby green style avatar for user champblahblah
    is a faxing machine an input or output devise
    (2 votes)
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    • starky seedling style avatar for user lmn32
      Depends on how you plugged it in.
      Is your faxing machine hooked up to your computer? Then we say its an input device for your computer!

      Did you decide to fax some of your word documents? Then we say your faxing machine is an output device for your computer, which outputs your word documents to the world!"

      is your computer hooked up to your fax machine, which is also hooked up to a projector? Then we can say that its both an input and an output device!

      TLDR: depends on how you're using it along with other computing systems 😃.
      (0 votes)
  • aqualine ultimate style avatar for user Huzaifah A.
    Are all sensors input devices ?
    (1 vote)
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  • blobby green style avatar for user LiuYecheng
    AI robots, interact through voice input for robots to make corresponding action?
    (1 vote)
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    • aqualine ultimate style avatar for user Martin
      A robot can respond to voice commands if it has an input device that allows it to receive voice input.
      So it would need a microphone to receive sounds and it would need code that allows it to translate the received sounds into instructions.
      (2 votes)
  • starky sapling style avatar for user Sharon
    Would a gumball Machine be an output machine and also is your brain and your nerves a input and output because the nerves Send signals to your brain
    (1 vote)
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    • starky seedling style avatar for user lmn32
      Very deep question! Yeah a gumball machine would be an output machine! The key here is to realize that the purpose of a gumball machine is to feed you gum. It's outputting a chemical blob into your mouth indirectly! However, if you think if a gumball machine from an owner's perspective, then its more of an input device because it's purpose is to make profits!

      Now about the brain, yes you can abstract away all the biology and the details(the fun part IMO😉), to create this abstract and dry model of your brain as an Input device and your nerves as an Output.
      Doing so might be useless, because biology tells us that there are different types of nerves, carrying information into and out of the brain, using different mechanisms. Just from the biological perspective, many medical professionals can beg to differ with your opinion.

      On a philosophical level: what really is consciences? There's a raging debate still going on about this in philosophical circles.

      On a psychological level:
      What makes something self aware?

      On a spiritual level:
      Why do our brains exist?

      Abstractions omit details. An "input/output idea" is an abstract way to model computers. It's only useful sometimes.
      (2 votes)