1.3 Input / Output & Buses



Data is transferred within computers in circuits called buses.

A bus is measured by the number of bits it can transfer at once. For example, a 16-bit bus can transfer 16 bits at once.

There are three key types of bus:

Address Bus

Data Bus

Control Bus

Sends the RAM address of where data is stored.

Address buses send data one way only: from the CPU to RAM.

Sends data from one component to another.

Data buses can send data both ways.

Sends control signals from the control unit to other components of the computer.


Input Devices

Output Devices

An input device allows data, such as text, images, video or sound, to be entered into a computer system. You should know how each of the following devices work and in which situations they might be used. This is not every input device but some of the more common ones.

Common input devices:

  • Mouse

  • Keyboard

  • Scanner

  • Controller

  • Microphone

  • Webcam

  • Chip Reader

  • OCR Scanner

  • OMR Scanner

  • Barcode Scanner

  • Graphics Tablet

  • Sensors (e.g. light or temperature)

  • Touch Screen

  • Remote Control

  • Biometric Scanner (e.g. fingerprint or iris)

  • Concept Keyboard

  • Sip / Puff Switch

There are many outputs created by a computer system, including printed documents, on-screen data and sound. You should know how each of the following devices work and in which situations they might be used. This is not every output device but some of the more common ones.

Other output devices:

  • Monitor

  • Printer (e.g. inkjet or laser)

  • Plotter

  • Speakers

  • Projector

  • Alarm

  • Light

  • Headphones

  • Touch Screen

  • Braille Terminal

Biometric Devices


A biometric device uses a human characteristic or behaviour as part of its security mechanism. Common examples of biometric input devices include fingerprint scanners, iris (eye) scanners or voice recognition. Facial recognition is becoming more popular, especially in locations such as airports where security is vital - scanners check that a person's face and their passport picture are similar.

Biometric devices can be used when security is paramount, such as government buildings or laboratories. Each employee must first input their information to a database, by scanning their fingerprint for example. Whenever the scanner scans a finger it searches in its database to see if the fingerprint matches one that it already holds. Only authorised employees will have already scanned their fingerprints so if there is no match then entry is not allowed. Biometric devices may be linked to output devices such as monitors or alarms.

Suitable Devices

It is not enough to just know about different input or output devices. In an exam you must be able to justify the most suitable input or output device for a given scenario, explaining the benefits of a particular device over another similar device.

For example a question might ask you to suggest a suitable device for someone with paralysis:

"When typing documents, a keyboard is the preferred device because of ease and familiarity but for someone with a disability, such as paralysis, a sip/puff switch may be used. This allows them to interact with the computer by blowing into the switch. However this is expensive and voice recognition might be used instead to verbally input commands."

Questo's Corner


a. In a computer system, what is a bus?

b. Describe the role of each of the 3 types of bus.

Input Devices:

a. Choose four input devices and describe how each can be used to input data to a computer system. How are they used, what type of data do they input and who would use them?.

Output Devices:

a. Do the same task as above but with four output devices.


Justify which input and output devices could be used in the following situations:

a. A teacher needs to take the class register.

b. A laboratory needs security so that only registered scientists can enter.

c. The school movie club wants to play Doctor Strange in the hall.

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