Most computer systems provide access to one or more auxiliary devices that supply specific functionality. Auxiliary devices generally appear outside the case and attach to an external port in some manner. They fall into these categories:
Devices, such as keyboards, that the system usually requires to perform useful tasks
Devices, such as printers, that the system can function without, but are critical to user needs
Nice-to-have appliances, such as webcams, that aren’t critical to support user needs, but make ...