The initial versions of the USB standard specified connectors that were easy to use and that would have acceptable life spans; revisions of the standard added smaller connectors useful for compact portable devices. Higher-speed development of the USB standard gave rise to another family of connectors to permit additional data paths. All versions of USB specify cable properties; version 3.x cables include additional data paths. The USB standard included power supply to peripheral devices; modern versions of the standard extend the power delivery limits for battery charging and devices requiring up to 240 watts. USB has been selected as the standard charging format for many mobile phones, reducing the proliferation of proprietary chargers.
Various legacy USB connectors along a centimeter ruler for scale. From left to right: Micro-B plug Proprietary UC-E6 connector used on many older Japanese cameras for both USB and analog AV output Mini-B plug Standard-A receptacle, non-compliant because USB does not allow extensions cables Standard-A plug Standard-B plug
Non-standard "USB extension cable", plug on the left, receptacle on the right. (USB does not allow extension cables. Non-standard cables may work but cannot be presumed reliable.)
A yellow charge-only "USB" Type-A receptacle and a USB 3.0 Type-A receptacle, both upside-down, on a front panel with card reader
A blue Standard-A USB receptacle without USB 3.0 contacts fitted
Universal Serial Bus (USB) is an industry standard that allows data exchange and delivery of power between many types of electronics. It specifies its architecture, in particular its physical interface, and communication protocols for data transfer and power delivery to and from hosts, such as personal computers, to and from peripheral devices, e.g. displays, keyboards, and mass storage devices, and to and from intermediate hubs, which multiply the number of a host's ports.
Various legacy USB and related connectors (left to right): USB Micro-B plug, proprietary UC-E6 plug, USB Mini-B plug, Standard-A-like receptacle (non-compliant), Standard-A plug, Standard-B plug. Shown with a centimeter ruler.
USB logo on the head of a standard Type-A (Standard-A) plug
A USB 2.0 PCI expansion card
USB 3.2 Gen 1(x1), Standard-A connectors labelled as USB 3.1 Gen 1 – originally simply named USB 3.0 and marketed as SuperSpeed USB (by USB 3.0 specification) and later named as USB 3.2 Gen 1x1 and marketed as SuperSpeed USB 5Gbps by the USB 3.2 specification