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Studio render of an exploded view of a USB peripheral, its housing, board and connector separated with nested frosted layers describing its parts

Topic · 2 min read

How USB describes a peripheral

A USB device reports structured information so the host can identify its functions and decide how to communicate with them. This description has several levels, each with a different role.

The bigger picture

A device can contain configurations, interfaces, and endpoints rather than one undifferentiated stream. Class information can describe a common function such as input or audio, while vendor-specific interfaces require their own documented interpretation. The operating system uses the reported structure to connect appropriate software with each exposed function. Interface descriptions can change when an accessory selects a different supported configuration.

The visible product name is a convenience for people; it is not a complete substitute for this structure. A multifunction accessory can create several inventory entries without being several separate physical products. These references explain the hierarchy and its limits so a descriptor, identifier, or endpoint is not mistaken for a retail specification, a serial number, or an electrical connector.

Reading map: How USB describes a peripheralFirst 1 topics in reading order: The bigger picture. Each topic links to its section or page.INSIDE THIS PAGEHow USB describes a peripheral1The bigger picture2 paragraphs

USB & Peripherals

Note these before you change anything

Useful facts to have to hand while reading about how usb describes a peripheral.

  • Which port the device was in, and whether a hub is involved
  • The device's name and status in Device Manager
  • Power management settings on USB root hubs
  • Any companion software the device relies on

USB & Peripherals: Input from a device (output devices run the other way)

  1. Devicekeyboard, mouse or pad
  2. Port or hubphysical connection
  3. Host controllermanages the bus
  4. Class driverfor example HID
  5. Applicationreceives the input
Conceptual schematic of a selected path, not every request. Reads from the device towards software. Real systems add services, filter drivers and firmware not shown. Highlighted: the layer a driver change affects.

Pages in How USB describes a peripheral

Thumbnail for USB descriptors and capability reporting: a USB flash drive with a short stack of, set beside an exploded view of a USB peripheral (How USB describes a peripheral)Reference · 2 min read

USB descriptors and capability reporting

USB descriptors are structured records that describe a device and the communication arrangements it supports. They let a host learn about interfaces and…

Thumbnail for USB interfaces and endpoints: a cutaway USB device with two internal compartments, each, set beside an exploded view of a USB peripheral (How USB describes a peripheral)Reference · 2 min read

USB interfaces and endpoints

An interface groups a device function, while an endpoint provides a communication channel within the USB model. Neither term should automatically be…

Thumbnail for Human Interface Device classes: a mouse, a gamepad and a single keyboard switch, set beside an exploded view of a USB peripheral (How USB describes a peripheral)Reference · 2 min read

Human Interface Device classes

The Human Interface Device class, often called HID, supplies a framework for reporting controls and input data. Keyboards and pointing devices are familiar…

Thumbnail for Composite USB devices: a USB headset base exploded into a small speaker, set beside an exploded view of a USB peripheral (How USB describes a peripheral)Reference · 2 min read

Composite USB devices

A composite USB device exposes more than one function through a single device connection. The operating system can manage those functions separately while…

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