Thunderbolt3 is twice as fast and uses reversible USB-C". Archived from the original on 3 June 2015 . Retrieved 2 June 2015. Upstream USB connectors supply power at a nominal 5V DC via the V_BUS pin to downstream USB devices. Use class information in the interface descriptors. This base class is defined to use in device descriptors to indicate that class information should be determined from the Interface Descriptors in the device.

Universal Serial Bus Specification (PDF) (Technical report). 1996. p.29. v1.0. Archived (PDF) from the original on 30 January 2018. USB-A is old, but it's been fairly reliable. Hopefully it'll be like the early days of USB where we still had serial and parallel ports, and for a while, USB devices were more expensive than the serial variety by a good margin. Eventually USB settled and everything ended up better.USB provides three isochronous (fixed-bandwidth) synchronization types, [76] all of which are used by audio devices: [77] Low-power and high-power devices remain operational with this standard, but devices using SuperSpeed can take advantage of increased available current of between 150mA and 900mA, respectively. [30] :9–9 With these cables, the type is whichever end of the cable isn’t the standard USB Type-A connector. So, for example, a cable with both a USB Type-A and a Type-C connector is a USB Type-C cable.

Many USB bridge / data transfer cables are still USB 2.0, but there are also a number of USB 3.0 transfer cables. Despite USB 3.0 being 10 times faster than USB 2.0, USB 3.0 transfer cables are only 2 - 3 times faster given their design. [ clarification needed] Universal Serial Bus Device Class Specification for Device Firmware Upgrade, Version 1.0" (PDF). USB Implementers Forum. 13 May 1999. pp.7–8. Archived from the original (PDF) on 24 August 2014 . Retrieved 8 September 2014. We also saw the introduction of the USB On-The-Go specification with USB 2.0, which allows smartphones and tablets with USB-based connectors to host other USB devices. For example, you can plug a mouse, USB thumb drive, or digital camera into the USB port on a Samsung tablet or Google Pixel phone. USB 3.0 / 3.1 / 3.2 (2008 / 2013 / 2017)

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USB 2.0 Specification". USB Implementers Forum. Archived from the original on 3 December 2017 . Retrieved 28 April 2019. Dan Froelich (20 May 2009). "Isochronous Protocol" (PDF). USB.org. Archived from the original (PDF) on 17 August 2014 . Retrieved 21 November 2014.

USB was designed to standardize the connection of peripherals to personal computers, both to exchange data and to supply electric power. It has largely replaced interfaces such as serial ports and parallel ports and has become commonplace on a wide range of devices. Examples of peripherals that are connected via USB include computer keyboards and mice, video cameras, printers, portable media players, mobile (portable) digital telephones, disk drives, and network adapters. Full Speed USB Maximum Theoretical Throughput". Microchip Technology Incorporated. 23 March 2021. Archived from the original on 26 March 2021 . Retrieved 23 March 2021.

Please note:

A USB connection is always between an A end, either a host or a downstream port of a hub, and a B end, either a peripheral device or the upstream port of a hub. Historically this was made clear by the fact that hosts had only Type-A ports and peripheral devices had only Type-B, and every (valid) cable had one Type-A plug and one Type-B plug. USB-C (Type-C) is a single connector that replaces all Type-A and Type-B connectors ( legacy connectors), so when both sides are modern equipment with USB-C ports they negotiate which is the host (A) and which is the device (B). The functionality of a USB device is defined by a class code sent to a USB host. This allows the host to load software modules for the device and to support new devices from different manufacturers. Universal Charging Solution". GSMA. 17 February 2009. Archived from the original on 30 November 2011 . Retrieved 12 December 2011.

For a host providing power to devices, USB has a concept of the unit load. Any device may draw power of one unit, and devices may request more power in these discrete steps. It is not required that the host provide requested power, and a device may not draw more power than negotiated. USB 3.0 Promoter Group Announces USB 3.2 Update" (PDF) (Press release). Beaverton, Oregon, US. 25 July 2017. Archived (PDF) from the original on 21 September 2017 . Retrieved 27 July 2017– via www.usb.org.

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The main difference between versions is the shape, as the rounding has been altered due to the increase of the number of pins; allowing a faster data transfer. USB runs with a 5 V power line, while FireWire supplies 12V and theoretically can supply up to 30V. 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. In the initial design, USB operated at a far lower data rate and used less sophisticated hardware. It was suitable for small peripherals such as keyboards and pointing devices.