Battery Charging Specification 1.1 Added support for dedicated chargers, host chargers behavior for devices with dead batteries a b "10 Power Rules", Universal Serial Bus Power Delivery Specification revision3.0, version1.1, USB Implementers Forum, archived from the original on June 1, 2012 , retrieved September 5, 2017 Universal Serial Bus 2.0 Specification, Section 7.2.1.3 Low-power Bus-powered Functions" (ZIP). usb.org. 27 April 2000. Archived from the original on 10 September 2013 . Retrieved 11 January 2014. Universal Serial Bus ( USB) is an industry standard that allows data exchange and delivery of power between many various 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. [2] USB was originally designed to standardize the connection of peripherals to computers, replacing various interfaces such as serial ports, parallel ports, game ports, and ADB ports, [3] and prior versions of USB became commonplace on a wide range of devices, such as keyboards, mice, cameras, printers, scanners, flash drives, smartphones, game consoles, and power banks. [4] [5] It has evolved into a standard to replace virtually all common ports on computers, mobile devices, peripherals, power supplies, and manifold other small electronics. In the current standard the USB-C connector replaces the many various connectors for power (up to 240W), displays (e.g. DisplayPort, HDMI), and many other uses, as well as all previous USB connectors. A bus-powered hub is a high-power device providing low-power ports. It draws 1 unit load for the hub controller and 1 unit load for each of at most 4 ports. The hub may also have some non-removable functions in place of ports. A self-powered hub is a device that provides high-power ports by supplementing the power supply from the host with its own external supply. Optionally, the hub controller may draw power for its operation as a low-power device, but all high-power ports must draw from the hub's self-power.

The Type-A plug. This plug has an elongated rectangular cross-section, inserts into a Type-A receptacle on a downstream port on a USB host or hub, and carries both power and data. Captive cables on USB devices, such as keyboards or mice, terminate with a Type-A plug. Lex Friedman (25 February 2013). "Review: Logitech's Ultrathin mini keyboard cover makes the wrong tradeoffs". macworld.com. Archived from the original on 3 November 2013 . Retrieved 29 October 2013. Smith, Ryan (September 22, 2014). "DisplayPort Alternate Mode for USB Type-C Announced - Video, Power, & Data All Over Type-C". AnandTech. Archived from the original on December 18, 2014 . Retrieved December 28, 2014.Connectors [ edit ] Comparison of legacy USB connector plugs, omitting the current standard Type-C plugs USB2.0 provides for a maximum cable length of 5 meters (16ft 5in) for devices running at high speed (480Mbit/s). [88] The operation modes USB3.2Gen2×2 and USB4Gen2×2 – or: USB3.2Gen2×1 and USB4Gen2×1 – are not interchangeable or compatible; all participating controllers must operate with the same mode.

A USB system consists of a host with one or more downstream facing ports (DFP), [52] and multiple peripherals, forming a tiered- star topology. Additional USB hubs may be included, allowing up to five tiers. A USB host may have multiple controllers, each with one or more ports. Up to 127 devices may be connected to a single host controller. [53] [30] :8–29 USB devices are linked in series through hubs. The hub built into the host controller is called the root hub.External Hard Drives: Some external hard drives feature USB Type B connectors to establish a high-speed connection with computers for data storage and retrieval. Cai Yan (31 May 2007). "China to enforce universal cell phone charger". EE Times. Archived from the original on 29 September 2007 . Retrieved 25 August 2007.

The following 10 biggest mobile phone companies have signed the MoU: Apple, LG, Motorola, NEC, Nokia, Qualcomm, Research In Motion, Samsung, Sony Ericsson, Texas Instruments (press release), Europa, archived from the original on July 4, 2009 Thunderbolt 3 uses USB-C cables; the USB4 specification allows hosts and devices and requires hubs to support interoperability with the standard using the Thunderbolt 3 Alternate Mode.While converters exist between certain legacy interfaces and USB, they might not provide a full implementation of the legacy hardware. For example, a USB-to-parallel-port converter might work well with a printer, but not with a scanner that requires bidirectional use of the data pins. The standard connectors were designed to be more robust than many past connectors. This is because USB is hot-swappable, and the connectors would be used more frequently, and perhaps with less care, than previous connectors. The three sizes of USB connectors are the default, or standard, format intended for desktop or portable equipment, the mini intended for mobile equipment, which was deprecated when it was replaced by the thinner micro size, all of which were deprecated in USB 3.2 in favor of Type-C. 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 color-coded (SuperSpeed is identified by blue).

Micro-USB was embraced as the "Universal Charging Solution" by the International Telecommunication Union (ITU) in October 2009. [18]

Because use of the USB logo is only permitted after compliance testing, the user can have confidence that a USB device will work as expected without extensive interaction with settings and configuration. Main article: USB-C The USB-C plug USB cable with a USB-C plug and a USB-C port on a notebook computer