USB Type-C is a specification for a small 24-pin reversible-plug connector for USB devices and USB cabling. The USB Type-C Specification 1.0 was published by the USB Implementers Forum and was finalized in August 2014. It was developed at roughly the same time as the USB 3.1 specification, but distinct from it.
The Type-C connectors connect to both hosts and devices, replacing various Type-B and Type-A connectors and cables with a standard meant to be future-proof. The 24-pin double-sided connector is similar in size to the micro-B connector, with a Type-C port measuring 8.4 millimetres (0.33 in) by 2.6 millimetres (0.10 in). The connector provides four power/ground pairs, two differential pairs for non-SuperSpeed data (though only one pair is populated in a Type-C cable), four pairs for high-speed data bus, two "sideband use" pins, and two configuration pins for cable orientation detection, dedicated biphase mark code (BMC) configuration data channel, and VCONN +5 V power for active cables. Connecting an older device to a host with a Type-C receptacle requires a cable or adapter with a Type-A or Type-B plug or receptacle on one end and a Type-C plug on the other end. Legacy adapters with a Type-C receptacle are "not defined or allowed" by the specification, due to their being able to create "many invalid and potentially unsafe" cable combinations.
Full-featured Type-C cables are active, electronically marked cables that contain a chip with an ID function based on the configuration channel and vendor-defined messages (VDMs) from the USB Power Delivery 2.0 specification. Type-C devices may optionally support bus power currents of 1.5 A and 3.0 A (at 5 V) in addition to baseline bus power provision; power sources can either advertise increased USB current through the configuration channel, or they can support the full power delivery specification using both BMC-coded configuration line and legacy BFSK-coded VBUS line.
Alternate modes dedicate some of the physical wires in the Type-C cable for direct device-to-host transmission of alternate data protocols. The four high-speed lanes, two sideband pins, and (for dock, detachable device and permanent cable applications only) two non-SuperSpeed data pins and one configuration pin can be used for alternate mode transmission. The modes are configured using VDMs through the configuration channel.