Connectors Type A and B
Comparison of USB connector plugs, excluding USB-C type plugs
The three sizes of USB connectors are the default or standard format intended for desktop or portable equipment, the mini intended for mobile equipment, and the thinner micro size, for low-profile mobile equipment such as mobile phones and tablets. There are five speeds for USB data transfer: Low Speed, Full Speed, High Speed (from version 2.0 of the specification), SuperSpeed (from version 3.0), and SuperSpeed+ (from version 3.1). The modes have differing hardware and cabling requirements. USB devices have some choice of implemented modes, and USB version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specification suggests that plugs and receptacles be colour-coded (SuperSpeed is identified by blue).
Unlike other data buses (such as Ethernet), USB connections are directed; a host device has "downstream" facing ports that connect to the "upstream" facing ports of devices. Only downstream facing ports provide power; this topology was chosen to easily prevent electrical overloads and damaged equipment. Thus, USB cables have different ends: A and B, with different physical connectors for each. Each format has a plug and receptacle defined for each of the A and B ends. USB cables typically have male plugs on each end, and the corresponding receptacle is usually on a computer or electronic device.
Connectors Type C (USB-C)
Developed at roughly the same time as the USB 3.1 specification, but distinct from it, the USB-C Specification 1.0 was finalized in August 2014 and defines a new small reversible-plug connector for USB devices. The USB-C plug connects to both hosts and devices, replacing various Type-A and Type-B connectors and cables with a standard meant to be future-proof.
