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

Sends the RAM address of where data is stored.

Data is only sent one way: from the CPU to RAM.

Data Bus

Sends data from one component to another.

Data buses can send data both ways.

Control Bus

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


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 works and in which situations they might be used. This is not every input device but some of the more common ones.

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 works and in which situations they might be used. This is not every output 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

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 essential, 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; entry is not allowed. Biometric devices may be linked to output devices such as monitors or alarms.

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 screen a film in the assembly hall.

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