USB

Universal Serial Bus: host and device roles, speeds, power and device classes.

Intermediate

Version	Speed name	Rate
USB 1.1	Low / Full speed	1.5 / 12 Mbit/s
USB 2.0	High speed	480 Mbit/s
USB 3.x	SuperSpeed	5–20 Gbit/s
USB4		20–80 Gbit/s

USB uses a differential pair (D+/D−). Devices declare classes — CDC (virtual serial port), HID (keyboard/mouse), MSC (storage), audio — so drivers aren't needed. Default power is 5 V at 500 mA (USB 2.0); USB-C Power Delivery negotiates up to 48 V × 5 A = 240 W.

On USB-C, a device needs 5.1 kΩ pull-down resistors on CC1 and CC2 to receive 5 V from a C-to-C charger.

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