Field Guide · concept

A peripheral is any device connected to a computer that extends what it can do, sitting outside the core CPU and memory and communicating with them over a bus.1

computer CPU + memory keyboard mouse webcam monitor printer speakers external drive INPUT OUTPUT bus: USB · Bluetooth · PCIe
Peripherals ring the computer and fall into three groups — input devices feed data in, output devices send results out, and storage devices hold data — each attaching over a bus such as USB, Bluetooth, or PCIe.

Overview

Peripherals are how a computer talks to the world, and they fall into three rough groups. Input peripherals feed data in — the keyboard, mouse, webcam, and scanners. Output peripherals send results out — the monitor, printer, and speakers. Storage peripherals hold data, like external drives.

All of them attach to the machine through an input/output interface such as USB, Bluetooth, or an expansion slot, and rely on driver software so the operating system can use them.

Categories

The same bus carries devices from every category; what differs is the direction data flows:

Category Data direction Examples
Input Into the computer Keyboard, mouse, webcam, scanner
Output Out of the computer Monitor, printer, speakers
Storage Both ways External drive, USB stick
Combined Both ways Touchscreen, all-in-one printer

Where it fits

The term draws the line between the computer proper and everything bolted onto it: a part inside the case on the core bus is a component, while a device hanging off an external port is a peripheral. The boundary is fuzzy — an internal drive and an external one differ mainly in where they plug in. For a software-defined radio, the RTL-SDR dongle is just another USB peripheral: the computer treats the radio front end as an input device streaming IQ data.

Sources

  1. Peripheral — Wikipedia, on peripherals as devices that extend a computer. ↩

See also