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What computers do: input, process, and output

All computers take inputs, and process them to give an output. Watch Vasu explain more.

Computers can be programmed to solve problems or complete tasks that make people’s lives easier. General purpose computers include desktop computers, laptops, and mobile phones. These devices can be programmed to perform many varied tasks. Among other things, you can use these computers to communicate with friends online, create picture collages, or play games.

Input, process, and output

Computers, no matter how they are programmed, work with inputs, processes, and outputs.


All computers accept inputs. An input is data that is entered into or received by a computer. This could include a user pressing a key on a keyboard, clicking a mouse to select something on screen, or tapping a touch pad.


The process determines what the computer does with the input. For example, in gaming software, pressing the letter A may be a directional control, moving a character in the game to a different place. A program contains the set of instructions that define the process.


The output is how the computer presents the results of the process. Outputs can be returned to the user in many ways such as text on a screen, printed materials, or as sound from a speaker.

Digital devices (computers) you use in your day-to-day life have inputs, processes, and outputs.

Digital camera

A digital camera with a button being pressed.

  • Input: pressing the button on the top
  • Process: capturing and storing a picture
  • Output: showing the image on the screen

Word processor (such as Microsoft Word or Google Docs)

Two hands typing on a keyboard and a screen with text.

  • Input: pressing a button on the keyboard
  • Process: checking which letter has been pressed and adding the letter to the document in its memory
  • Output: showing the correct letter on the screen

Instructions and programs

A program is a set of instructions that a computer can run. Programs are clear, ordered, and in a language that computers can follow.

Programming languages are used to write instructions for computers. There are many different types of programming languages and all of them have the ability to:

  • Accept input data
  • Process decisions based on conditions being met
  • Carry out calculations
  • Repeat instructions
  • Output information

Programming is a creative task: there is no right or wrong way to complete a task, in the same way that there is no right or wrong way to paint a picture. There are choices to be made, and one way may seem better than another, but that doesn’t mean the other is wrong! With the right skills and experience, a programmer can craft software to solve an unlimited number of problems — from telling you when your next train will arrive to playing your favourite music. The possibilities are constrained only by your imagination. That’s why I love programming.

An animated GIF of cartoon of a computer following instructions as text appears on the screen. 1. turn and face the cliff 2. walk towards the cliff 3. stop at the edge of the cliff 4. jump off the cliff

What makes up a program?

When you create a program for a computer, you give it a set of instructions, which it will run one at a time in order, precisely as given. If you told a computer to jump off a cliff, it would!

1. Turn and face the cliff
2. Walk towards the cliff
3. Stop at the edge of the cliff
4. Jump off the cliff

To stop computers constantly falling off cliffs, they can also make choices about what to do next:

If I won't survive the fall, don't jump off the cliff.

Computers never get bored and are really good at doing the same thing over and over again. Instruction 2 above might look in more detail like this:

 2a. Left foot forward
2b. Right foot forward
2c. Go back to instruction 2a

An animated GIF of a cartoon computer walking forwards, repeatedly taking a step with one foot and then with the other.

These three concepts are the basic logical structures in computer programming:

  1. Sequence: running instructions in order
  2. Selection: making choices
  3. Repetition: doing the same thing more than once, also called ‘iteration’

I’ll explain these in more detail as you go through the course.

Add to these concepts the ability to deal with inputs and outputs and to store data, and you have the tools to solve the majority of all computing problems.


Why is it important to learn that computers only follow the instructions that they have been given? Give your view and discuss this in the comments section.

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Introduction to Programming with Scratch

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