Is a scanner an input or output device?

It’s important to understand whether a scanner is an input or output device so that you can better appreciate how a computer works. A computer is made up of a lot of different parts so it can be difficult to imagine how they fit together, particularly as technology has improved and scanners now come packaged with printers and fax machines.

A scanner is an input device because it sends data to the computer. It converts physical media like paper or a picture to a digital format and sends it to your computer. Information always flows from the scanner into the computer. 

Scanners have become incredibly popular sInce the decline of the fax machine. They are now the defacto way of digitizing documents so they can then be sent via email.

Let’s explore why a scanner is an input device and take a look at how information typically flows from a scanner to your computer.

Is a scanner an input device?

Is a scanner an input or output device?

A scanner is an input device that sends information to your computer’s processor. It does not receive any data or instructions back from the computer. The flow of data is always inward to the computer which is why a scanner is considered an input device rather than an output device. 

The most common type of scanner is a flatbed scanner, it’s the type that most people use at home and at work. They typically take a single sheet of paper at a time, scan it, then send it to your computer. However, there are a few other types of scanners, all of which are input devices: 

  • Sheet-fed scanners – these are typically used for large collections of loose documents. Businesses use them for documents and libraries sometimes use them for disbound books.
  • Hand-held scanners – scan a single document at a time and rely on the user to hover over the document with a scanner to capture the information. 
  • Drum scanners – these are the best scanners on the market and are generally used for commercial graphic design. They can turn high-quality photos into large-scale posters.


Despite their different uses, all the scanners mentioned are input devices. Their primary purpose is to provide your computer with data in the form of digital images or documents.

A keyboard is an input device similar to a scanner. When you press a key down, instructions are sent to the central processing unit (CPU) which then sends it on to other parts of the system to be actioned. A scanner works in a similar manner. But rather than sending keystrokes it sends scanned documents and images. 

In contrast to a scanner, a printer is an output device. It only ever receives data and instructions from the computer. A printer takes these instructions and prints them onto a physical medium like paper. It never sends instructions or data back to the CPU to be acted upon which is the opposite of input devices.

If you are ever having trouble remembering whether a scanner is an input or output device, just imagine the flow of information. A scanner only ever sends data into the processor. It does not receive data from your computer. 

Why Is a scanner an input device?

A scanner is an input device because it sends data into your computer but does not receive instructions from it. It sends your computer digital copies of the documents you have scanned which are then distributed to the relevant parts of the computer. 

The diagram below shows the flow of information in and out of a computer. After your documents are scanned they are sent to the CPU. The CPU processes the information and then either stores it or forwards it to an output device. 

Information flow inside a computer

For input devices, like a scanner and mouse, Information starts outside the computer and flows inwards. For output devices like speakers or a monitor, information is sent from inside the computer and flows outwards. 

In contrast, the hard drive is a storage device. It does send and receive data from the CPU. But unlike input and output devices, its primary job is to store data. With a hard drive, the data remains inside the computer, it is the CPU’s job as a processor, to then distribute the data. 

Can a scanner be used as an output device?

With the advent of all-in-one devices, it has become harder to establish the limits of the technology you are using. 

If your scanner also has a printer does this make it an output device? Even in all-in-one devices, a scanner can not be used as an output device. Hardware with scanning and printing functionality operate independently from each other. 

Devices that have multiple functionalities like scanning, printing, and faxing, operate differently from normal scanners. The scanning element still operates as an input device and the printing element still functions as an output device. 

However, the device both sends and receives data to your computer. The scanner will send data to the CPU and the printer will receive data from the CPU. Despite this two-way information exchange coming from a single device, the independent elements remain input or outputs, they do not ever act as both. 

It means a scanner will never act as an output device nor a printer as an input device. 

It’s similar to how the touch screen on your phone works. The display element only outputs information and the touch element that sits on top of it only inputs information. Despite all being in one device, their responsibilities remain separate. 

Conclusion

A scanner is an input device that sends physical copies of documents to a computer in a digital format. Scanners only send data to your computer to be processed, they don’t ever receive information that needs to be processed.

The flow of information inwards to the computer is what makes a scanner an input device. In contrast, for output devices, the information flows outwards to then be processed by them.