Editing USB (section)

== Overview ==
USB was designed to standardize the connection of [[peripheral]]s to personal computers, both to exchange data and to supply electric power. It has largely replaced interfaces such as [[serial port]]s and [[parallel port]]s and has become commonplace on various devices. Peripherals connected via USB include computer keyboards and mice, video cameras, printers, portable media players, mobile (portable) digital telephones, disk drives, and network adapters.

USB connectors have been increasingly replacing other types of charging cables for portable devices.<ref>{{cite web |url=https://interestingengineering.com/culture/eu-adopts-usb-c-charging-standard |title=Universal charger rule: USB-C becomes mandatory for devices sold in EU |access-date=2025-04-26}}</ref><ref>{{cite web |url=https://www.theregister.com/2024/10/14/uk_usbc_charging_standard/ |title=UK ponders USB-C as common charging standard |access-date=2025-04-26}}</ref><ref>{{cite web |url=https://www.hwe.design/design-fundamentals/usb-charging-basics |title=USB Charging |access-date=2025-04-26}}</ref>

USB connector interfaces are classified into three types: the many various ''legacy'' Type-A (upstream) and Type-B (downstream) connectors found on ''hosts'', ''hubs'', and ''peripheral devices'', and the modern Type-C ([[USB-C]]) connector, which replaces the many legacy connectors as the only applicable connector for USB4.

The Type-A and Type-B connectors came in Standard, Mini, and Micro sizes. The standard format was the largest and was mainly used for desktop and larger peripheral equipment. The Mini-USB connectors (Mini-A, Mini-B, Mini-AB) were introduced for mobile devices. Still, they were quickly replaced by the thinner Micro-USB connectors (Micro-A, Micro-B, Micro-AB). The Type-C connector, also known as USB-C, is not exclusive to USB, is the only current standard for USB, is required for USB4, and is required by other standards, including modern DisplayPort and Thunderbolt. 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.<ref>{{cite web |url=https://www.usb.org/sites/default/files/documents/cabconn20.pdf |title=Universal Serial Bus Cables and Connectors Class Document Revision 2.0 |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite web |url=https://www.usb.org/sites/default/files/documents/usb_type-c_specification_1_0.pdf |title=Universal Serial Bus Type-C Cable and Connector Specification Revision 1.0 |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

USB specifications provide backward compatibility, usually resulting in decreased signaling rates, maximal power offered, and other capabilities. The USB 1.1 specification replaces USB 1.0. The USB 2.0 specification is backward-compatible with USB 1.0/1.1. The USB 3.2 specification replaces USB 3.1 (and USB 3.0) while including the USB 2.0 specification. USB4 "functionally replaces" USB 3.2 while retaining the USB 2.0 bus operating in parallel.<ref name="USB31Spec" /><ref name=USB2Spec/><ref name=USB32101Spec/><ref name=USB42Spec/>

The USB&nbsp;3.0 specification defined a new architecture and protocol named ''SuperSpeed'' (aka ''SuperSpeed USB'', marketed as ''SS''), which included a new lane for a new signal coding scheme (8b/10b symbols, 5&nbsp;Gbit/s; later also known as ''Gen 1'') providing full-duplex data transfers that physically required five additional wires and pins, while preserving the USB&nbsp;2.0 architecture and protocols and therefore keeping the original four pins/wires for the USB&nbsp;2.0 backward-compatibility resulting in 9 wires (with 9 or 10 pins at connector interfaces; ID-pin is not wired) in total.

The USB&nbsp;3.1 specification introduced an ''Enhanced SuperSpeed System'' – while preserving the ''SuperSpeed'' architecture and protocol (''SuperSpeed USB'') – with an additional ''SuperSpeedPlus'' architecture and protocol (aka ''SuperSpeedPlus USB'') adding a new coding schema (128b/132b symbols, 10&nbsp;Gbit/s; also known as ''Gen 2''); for some time marketed as ''SuperSpeed+'' (''SS+'').

The USB&nbsp;3.2 specification<ref name=USB32Spec/> added a second lane to the ''Enhanced SuperSpeed System'' besides other enhancements so that the ''SuperSpeedPlus USB'' system part implements the ''Gen 1×2'', ''Gen 2×1,'' and ''Gen 2×2'' operation modes. However, the ''SuperSpeed USB'' part of the system still implements the one-lane ''Gen 1×1'' operation mode. Therefore, two-lane operations, namely ''USB&nbsp;3.2 Gen&nbsp;1×'''2''' ''(10&nbsp;Gbit/s) and ''Gen&nbsp;2×'''2''' ''(20&nbsp;Gbit/s), are only possible with Full-Featured USB-C. As of 2023, they are somewhat rarely implemented; Intel, however, started to include them in its 11th-generation SoC processor models, but Apple never provided them. On the other hand, ''USB&nbsp;3.2 Gen&nbsp;1(×1)'' (5&nbsp;Gbit/s) and ''Gen&nbsp;2(×1)'' (10&nbsp;Gbit/s) have been quite common for some years.

===Connector type quick reference===
{{Main|USB hardware#Connectors}}
Each USB connection is made using two connectors: a ''receptacle'' and a ''plug''. Pictures show only receptacles:
{{mw-datatable}}
{| class="wikitable mw-datatable" style="text-align:center; margin-left:auto; margin-right:auto;"
|+ Available connectors by USB standard
|-
! colspan=2|Standard
! [[#1.x|USB 1.0]]<br />1996
! [[#1.x|USB 1.1]]<br />1998
! [[#2.0|USB 2.0]]<br />2000
! USB 2.0<br />Revised
! [[USB 3.0]]<br />2008
! [[USB 3.0#3.1|USB 3.1]]<br />2013
! [[USB 3.0#3.2|USB 3.2]]<br />2017
! [[USB4]]<br />2019
! [[USB4|USB4 2.0]]<br />2022
|-
! rowspan="4" | Max Speed
! Recommended marketing<br>names from 2022{{R|USBDataPerformance}}
| colspan="2" | '''Basic-Speed'''
| rowspan="3" colspan="2" | '''High-Speed'''
| '''USB 5Gbps'''
| '''USB 10Gbps'''
| '''USB 20Gbps'''
| rowspan="2" |'''USB 40Gbps'''
| rowspan="2" | '''USB 80Gbps'''
|-
! Original label
| rowspan="2" colspan="2" | ''Low-Speed & Full-Speed''
| ''SuperSpeed'', or ''SS''
| ''SuperSpeed+'', or ''SS+''
| ''SuperSpeed USB 20Gbps''
|-
! Operation mode
| USB&nbsp;3.2 Gen&nbsp;1×1
| USB&nbsp;3.2 Gen&nbsp;2×1
| USB&nbsp;3.2 Gen&nbsp;2×2
| USB4 Gen&nbsp;3×2
| USB4 Gen&nbsp;4×2
|-
! Signaling rate
| colspan="2" | 1.5 Mbit/s & 12&nbsp;Mbit/s
| colspan="2" | 480 Mbit/s
| 5 Gbit/s
| 10 Gbit/s
| 20 Gbit/s
| 40 Gbit/s
| 80 Gbit/s
|-
! rowspan="9" | Connector
! {{nowrap|Standard-A}}
| colspan="2" | [[File:USB Type-A receptacle White.svg|75px]]
| colspan="2" | [[File:USB Type-A receptacle Black.svg|75px]]
| colspan="2" | [[File:USB 3.0 Type-A receptacle blue.svg|75px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Type-A receptacle blue.svg|50px]]<ref  group="rem" name="OLOp">Limited to max speed at 10&nbsp;Gbit/s, since only one-lane (''×1'') operation mode is possible.</ref>
| colspan="2" rowspan="2" {{N/A}}
|-
! {{nowrap|Standard-B}}
| colspan="4" | [[File:USB Type-B receptacle.svg|x60px]]
| colspan="2" | [[File:USB 3.0 Type-B receptacle blue.svg|x75px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Type-B receptacle blue.svg|50px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Mini-A}}
| rowspan="3" |<ref group="rem" name="bc1.1">[[Backward compatibility]] given.</ref>
| colspan="3" | [[File:USB Mini-A receptacle.svg|67x67px]]
| colspan="5" rowspan="3" {{N/A}}
|-
! {{nowrap|Mini-AB}}<ref group="rem" name="RecOnly">Only as receptacle.</ref><ref group="rem">Accepts both Mini-A and Mini-B plugs.</ref>
| colspan="3" | [[File:USB_Mini-AB_receptacle.svg|75x75px]]
|-
! {{nowrap|Mini-B}}
| colspan="3" | [[File:USB Mini-B receptacle.svg|67x67px]]
|-
! {{nowrap|Micro-A}}<ref group="rem" name="PlugOnly">Only as plug.</ref>
| colspan="3" rowspan="3" |&nbsp;<ref group="rem" name="bc1.1"/><ref group="rem" name="bc2"/>
| [[File:USB Micro-A.svg|alt=|frameless|75x75px]]
| colspan="2" | [[File:USB 3.0 Micro-A.svg|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Micro-A.svg|60px]]<ref group="rem" name="OLOp"/>
| colspan="2" rowspan="3" {{N/A}}
|-
! {{nowrap|Micro-AB}}<ref group="rem" name="RecOnly"/><ref group="rem">Accepts both Micro-A and Micro-B plugs.</ref>
| [[File:USB Micro-AB receptacle.svg|75x75px]]
| colspan="2" | [[File:USB micro AB SuperSpeed.png|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB micro AB SuperSpeed.png|60px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Micro-B}}
| [[File:USB Micro B receptacle pinout.svg|alt=|frameless|75x75px]]
| colspan="2" | [[File:USB 3.0 Micro-B receptacle.svg|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Micro-B receptacle.svg|60px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Type-C}} {{nowrap|(USB-C)}}
| colspan="3" |<ref group="rem" name="bc2">Backward compatibility given by USB 2.0 implementation.</ref>
| colspan="6" style="font-size:60%"| [[File:USB Type-C Receptacle Pinout.svg|117x117px]]<br/>(Enlarged to show detail)
|- style="background:#FEE4BA"
| ''Remarks:''
| scope=col colspan=10 | {{reflist|group="rem"}}
|}

=== Objectives ===
The Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, such as cell phones, computer accessories, and monitors, when compared with previously existing standard or ''ad hoc'' proprietary interfaces.<ref name="JA2015">Axelson, Jan (2015). ''USB Complete: The Developer's Guide, Fifth Edition'', Lakeview Research LLC, {{ISBN|1931448280}}, pp. 1-7.</ref>

From the computer user's perspective, the USB interface improves ease of use in several ways:
* The USB interface is self-configuring, eliminating the need for the user to adjust the device's settings for speed or data format, or configure [[interrupt]]s, input/output addresses, or direct memory access channels.<ref>{{cite web |website=PC |url=https://www.pcmag.com/encyclopedia/term/44434/how-to-install-a-pc-peripheral |title=Definition of: how to install a PC peripheral |publisher=[[Ziff Davis]] |access-date=17 February 2018 |archive-date=22 March 2018 |archive-url=https://web.archive.org/web/20180322020256/https://www.pcmag.com/encyclopedia/term/44434/how-to-install-a-pc-peripheral |url-status=live}}</ref>
* USB connectors are standardized at the host, so any peripheral can use most available receptacles.
* USB takes full advantage of the additional processing power that can be economically put into peripheral devices so that they can manage themselves. As such, USB devices often do not have user-adjustable interface settings.
* The USB interface is [[hot-swappable]] (devices can be exchanged without shutting the host computer down).
* Small devices can be powered directly from the USB interface, eliminating the need for additional power supply cables.
* Because the 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.
* The USB interface defines protocols for recovery from common errors, improving reliability over previous interfaces.<ref name="JA2015"/>
* Installing a device that relies on the USB standard requires minimal operator action. When a user plugs a device into a port on a running computer, it either entirely automatically configures using existing [[device driver]]s, or the system prompts the user to locate a driver, which it then installs and configures automatically.

The USB standard also provides multiple benefits for hardware manufacturers and software developers, specifically in the relative ease of implementation:
* The USB standard eliminates the requirement to develop proprietary interfaces to new peripherals.
* The wide range of transfer speeds available from a USB interface suits devices ranging from keyboards and mice up to streaming video interfaces.
* A USB interface can be designed to provide the best available [[Latency (engineering)|latency]] for time-critical functions or can be set up to do background transfers of bulk data with little impact on system resources.
* The USB interface is generalized with no signal lines dedicated to only one function of one device.<ref name="JA2015"/>

===Limitations===
As with all standards, USB possesses multiple limitations to its design:
* USB cables are limited in length, as the standard was intended for peripherals on the same tabletop, not between rooms or buildings. However, a USB port can be connected to a [[Gateway (telecommunications)|gateway]] that accesses distant devices.
* USB data transfer rates are slower than those of other interconnects such as [[100 Gigabit Ethernet]].
* USB has a strict [[tree network]] topology and [[Master–slave (technology)|master/slave]] protocol for addressing peripheral devices; slave devices cannot interact with one another except via the host, and two hosts cannot communicate over their USB ports directly. Some extension to this limitation is possible through [[USB On-The-Go]], Dual-Role-Devices<ref>{{cite web |url=https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go/ |title=To USB or Not to USB: USB Dual Role replaces USB On-The-Go |last=Huang |first=Eric |work=synopsys.com |date=3 May 2018 |access-date=21 July 2021 |archive-date=25 July 2021 |archive-url=https://web.archive.org/web/20210725064610/https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go/ |url-status=live}}</ref> and [[protocol bridge]].
* A host cannot broadcast signals to all peripherals at once; each must be addressed individually.
* While converters exist between certain [[Legacy system|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.

For a product developer, using USB requires the implementation of a complex protocol and implies an "intelligent" controller in the peripheral device. Developers of USB devices intended for public sale generally must obtain a USB ID, which requires that they pay a fee to the [[USB Implementers Forum]] (USB-IF). Developers of products that use the USB specification must sign an agreement with the USB-IF. Use of the USB logos on the product requires annual fees and membership in the organization.<ref name="JA2015"/>