EMZETT.Peripherals
In short: All external devices connected to a computer but not part of its core hardware (CPU, RAM, motherboard) — e.g. mouse, keyboard, printer, external hard drives.
In more detail: Peripherals are usually connected via standard interfaces like USB, so they’re compatible across manufacturers. A rough distinction is made between input devices (mouse, keyboard, microphone), output devices (monitor, printer) and storage devices (external hard drives).
In Depth
Distinction from core hardware
The distinction between “core hardware” and “peripherals” is based on whether a component is strictly necessary for the basic operation of the computer: every functioning computer must have a CPU, RAM and motherboard, while peripherals merely extend HOW humans interact with this core system, or what additional functions it offers — a server, for example, often runs completely without a connected mouse, keyboard or monitor, since administration happens exclusively over the network (e.g. via SSH).
Edge cases of the classic categories
The three classic categories — input, output, storage — don’t fully cover every case: some devices combine several roles (a touchscreen is both an output and an input device, a multifunction printer combines a printer and scanner in one housing, a webcam combines video and often audio capture too). Some device classes also don’t fit particularly well into any of the three categories — for example a capture device that feeds an external video/audio signal into the system, or a docking station, which itself bundles several other peripherals.
From cable chaos to unification
Historically, peripherals were connected via very different, often manufacturer-specific connectors: serial interfaces (RS-232, for modems and early mice), parallel interfaces (classically for printers, could transmit several bits at once instead of one after another), PS/2 (a round connector format specifically for mouse and keyboard, mechanically coded differently so the two couldn’t be mixed up), and various other proprietary formats. Each of these connector types had its own electrical specifications, its own drivers and often its own speed limits — a user had to know exactly which device went into which port.
USB as a unifying step
The unification onto USB as a universal standard from the mid-1990s onwards was one of the biggest simplification steps in PC history: since then, practically any peripheral, regardless of manufacturer, can be connected via the same physical interface, the operating system automatically recognises most device classes (plug and play) without manual driver installation, and a single connector type today covers mice, keyboards, printers, external storage, audio devices and many other categories at once. This consolidation continues with USB-C, which additionally also enables video output (DisplayPort Alternate Mode) and high charging power over the same universal connector.