[3] Early 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] USB has since evolved into a standard to replace virtually all common ports on computers, mobile devices, peripherals, power supplies, and manifold other small electronics.

USB4 enhances the data transfer and power delivery functionality with ... a connection-oriented, tunneling architecture designed to combine multiple protocols onto a single physical interface so that the total speed and performance of the USB4 Fabric can be dynamically shared.

[9] USB was designed to standardize the connection of peripherals to personal computers, both to exchange data and to supply electric power.

It is reversible and can support various functionalities and protocols, including USB; some are mandatory, and many are optional, depending on the type of hardware: host, peripheral device, or hub.

[10][11] USB specifications provide backward compatibility, usually resulting in decreased signaling rates, maximal power offered, and other capabilities.

[12] A group of seven companies began the development of USB in 1995:[16] Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel.

[18][19] A consortium lead by Apple, and containing Sony, Panasonic (Matsushita), LG, Toshiba, Hitachi, Cannon, Philips Electronics, Compaq, Thomson and Texas Instruments, would develop the concept further, from 1986, as the IEEE 1394 firewire standard and patent pool.

When flow control, packet framing and protocol overhead are considered, it is realistic for about two-thirds of the raw throughput, or 330 MB/s to transmit to an application.

The increase in bandwidth is a result of two-lane operation over existing wires that were originally intended for flip-flop capabilities of the USB-C connector.

[52][needs update] The USB4 specification states that the following technologies shall be supported by USB4:[45] Because of the previous confusing naming schemes, USB-IF decided to change it once again.

This version incorporates the following ECNs: A USB system consists of a host with one or more downstream facing ports (DFP),[61] and multiple peripherals, forming a tiered-star topology.

Endpoints are defined and numbered by the device during initialization (the period after physical connection called "enumeration") and so are relatively permanent, whereas pipes may be opened and closed.

Other competing standards for external drive connectivity include eSATA, ExpressCard, FireWire (IEEE 1394), and most recently Thunderbolt.

Another use for USB mass storage devices is the portable execution of software applications (such as web browsers and VoIP clients) with no need to install them on the host computer.

[68][69] Media Transfer Protocol (MTP) was designed by Microsoft to give higher-level access to a device's filesystem than USB mass storage, at the level of files rather than disk blocks.

[citation needed] Active converters that connect USB keyboards and mice (usually one of each) to PS/2 ports also exist.

[88][76][93] Asynchronous has the benefit of being untied from the computer's clock, but the disadvantage of requiring sample rate conversion when combining multiple sources.

The USB specification requires that the cable plug and receptacle be marked so the user can recognize the proper orientation.

[95][96][97] USB 2.0 provides for a maximum cable length of 5 meters (16 ft 5 in) for devices running at high speed (480 Mbit/s).

[clarification needed] The USB 3.0 specification introduced an A-to-A cross-over cable without power for connecting two PCs.

Under the most recent specifications, USB supports most scenarios connecting systems directly with a Type-C cable.

[100] USB-C also allows for Type-C Current as a replacement for USB BC, signaling power availability in a simple way, without needing any data connection.

[102][103] In addition to standard USB, there is a proprietary high-powered system known as PoweredUSB, developed in the 1990s, and mainly used in point-of-sale terminals such as cash registers.

It is a proprietary technology, not standardized by the USB Implementers Forum and typically requires a separate device driver on the computer.

At first, USB was considered a complement to FireWire (IEEE 1394) technology, which was designed as a high-bandwidth serial bus that efficiently interconnects peripherals such as disk drives, audio interfaces, and video equipment.

The chipset and drivers used to implement USB and FireWire have a crucial impact on how much of the bandwidth prescribed by the specification is achieved in the real world, along with compatibility with peripherals.

This has made PoE popular for Voice over IP telephones, security cameras, wireless access points, and other networked devices within buildings.

This gives Ethernet a significant safety advantage over USB with peripherals such as cable and DSL modems connected to external wiring that can assume hazardous voltages under certain fault conditions.

eSATAp support can be added to a desktop machine in the form of a bracket connecting the motherboard SATA, power, and USB resources.