Editing USB (section)

== Comparisons with other connection methods ==
=== FireWire (IEEE 1394) ===
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.

The most significant technical differences between FireWire and USB include:

* USB networks use a [[star network|tiered-star]] topology, while IEEE&nbsp;1394 networks use a [[tree network|tree]] topology.
* USB&nbsp;1.0, 1.1, and 2.0 use a "speak-when-spoken-to" protocol, meaning that each peripheral communicates with the host when the host specifically requests communication. USB&nbsp;3.0 allows for device-initiated communications towards the host. A FireWire device can communicate with any other node at any time, subject to network conditions.
* A USB network relies on a single host at the top of the tree to control the network. All communications are between the host and one peripheral. In a FireWire network, any capable node can control the network.
* USB runs with a 5&nbsp;[[Volts|V]] power line, while FireWire supplies 12&nbsp;V and theoretically can supply up to 30&nbsp;V.
* Standard USB hub ports can provide from the typical 500&nbsp;mA/2.5&nbsp;W of current, only 100&nbsp;mA from non-hub ports. USB&nbsp;3.0 and USB On-The-Go supply 1.8&nbsp;A/9.0&nbsp;W (for dedicated battery charging, 1.5&nbsp;A/7.5&nbsp;W full bandwidth or 900&nbsp;mA/4.5&nbsp;W high bandwidth), while FireWire can in theory supply up to 60&nbsp;watts of power, although 10 to 20&nbsp;watts is more typical.

These and other differences reflect the differing design goals of the two buses: USB was designed for simplicity and low cost, while FireWire was designed for high performance, particularly in time-sensitive applications such as audio and video. Although similar in theoretical maximum signaling rate, FireWire&nbsp;400 is faster than USB&nbsp;2.0 high-bandwidth in real-use,<ref>{{cite web|title=FireWire vs. USB 2.0|url=http://www.qimaging.com/support/pdfs/firewire_usb_technote.pdf|publisher=QImaging|access-date=20 July 2010|url-status=live|archive-url=https://web.archive.org/web/20101011050049/http://www.qimaging.com/support/pdfs/firewire_usb_technote.pdf|archive-date=11 October 2010}}</ref> especially in high-bandwidth use such as external hard drives.<ref>{{cite web |url= http://www.cwol.com/firewire/firewire-vs-usb.htm |title= FireWire vs. USB&nbsp;2.0 – Bandwidth Tests |access-date= 25 August 2007 |url-status=live |archive-url= https://web.archive.org/web/20070812045719/http://www.cwol.com/firewire/firewire-vs-usb.htm |archive-date= 12 August 2007}}</ref><ref>{{cite web |url=https://www.pricenfees.com/digit-life-archives/usb-2-0-vs-firewire |title=USB&nbsp;2.0 vs FireWire |publisher=Pricenfees |access-date=25 August 2007 |url-status=live |archive-url=https://web.archive.org/web/20161016063120/https://www.pricenfees.com/digit-life-archives/usb-2-0-vs-firewire |archive-date=16 October 2016}}</ref><ref>{{cite magazine |url=https://www.pcmag.com/article2/0,4149,847716,00.asp |title=The Great Interface-Off: FireWire Vs. USB&nbsp;2.0 |magazine=PC Magazine |access-date=25 August 2007 |last=Metz |first=Cade |date=25 February 2003 |url-status=live |archive-url=https://web.archive.org/web/20070930190355/http://www.pcmag.com/article2/0,4149,847716,00.asp |archive-date=30 September 2007 }}</ref><ref>{{cite web|url=http://www.g4tv.com/techtvvault/features/39129/USB_20_Versus_FireWire_pg3.html|title=USB&nbsp;2.0 Versus FireWire|access-date=25 August 2007|author=Heron, Robert|publisher=TechTV|url-status=live|archive-url=https://web.archive.org/web/20070929121843/http://www.g4tv.com/techtvvault/features/39129/USB_20_Versus_FireWire_pg3.html|archive-date=29 September 2007}}</ref> The newer FireWire&nbsp;800 standard is twice as fast as FireWire&nbsp;400 and faster than USB&nbsp;2.0 high-bandwidth both theoretically and practically.<ref>{{cite web | url = http://www.usb-ware.com/firewire-vs-usb.htm | title = FireWire vs. USB&nbsp;2.0 | publisher = USB Ware | access-date = 19 March 2007 | url-status=live | archive-url = https://web.archive.org/web/20070316072513/http://www.usb-ware.com/firewire-vs-usb.htm | archive-date = 16 March 2007}}</ref> However, FireWire's speed advantages rely on low-level techniques such as [[direct memory access]] (DMA), which in turn have created opportunities for security exploits such as the [[DMA attack]].

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.<ref>{{cite web |url=http://www.anandtech.com/mb/showdoc.aspx?i=2602&p=15 |title=Firewire and USB Performance |access-date=1 February 2008 |last=Key |first=Gary |date=15 November 2005 |url-status=live |archive-url=https://web.archive.org/web/20080423214619/http://www.anandtech.com/mb/showdoc.aspx?i=2602&p=15 |archive-date=23 April 2008}}</ref>

=== Ethernet ===
The ''IEEE 802.3af'', ''802.3at'', and ''802.3bt'' [[Power over Ethernet]] (PoE) standards specify more elaborate power negotiation schemes than powered USB. They operate at 48&nbsp;V&nbsp;[[Direct current|DC]] and can supply more power (up to 12.95&nbsp;W for ''802.3af'', 25.5&nbsp;W for ''802.3at'', a.k.a. ''PoE+'', 71&nbsp;W for ''802.3bt'', a.k.a. ''4PPoE'') over a cable up to 100&nbsp;meters compared to USB&nbsp;2.0, which provides 2.5&nbsp;W with a maximum cable length of 5&nbsp;meters. This has made PoE popular for [[Voice over IP]] telephones, [[security camera]]s, [[wireless access point]]s, and other networked devices within buildings. However, USB is cheaper than PoE provided that the distance is short and power demand is low.

[[Ethernet]] standards require electrical isolation between the networked device (computer, phone, etc.) and the network cable up to 1500&nbsp;V&nbsp;AC or 2250&nbsp;V&nbsp;DC for 60&nbsp;seconds.<ref>{{cite web | url = http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf | title = 802.3, Section 14.3.1.1 | publisher = IEEE | url-status=dead | archive-url = https://web.archive.org/web/20101206030247/http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf | archive-date = 6 December 2010}}</ref> USB has no such requirement as it was designed for peripherals closely associated with a host computer, and in fact it connects the peripheral and host grounds. 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.<ref>{{cite web|date=8 March 2010|title=Powerbook Explodes After Comcast Plugs in Wrong Cable|url=http://consumerist.com/2006/12/powerbook-explodes-after-comcast-plugs-in-wrong-cable.html|url-status=dead|archive-url=https://web.archive.org/web/20100625052120/http://consumerist.com/2006/12/powerbook-explodes-after-comcast-plugs-in-wrong-cable.html|archive-date=25 June 2010|access-date=22 June 2010|publisher=Consumerist}}</ref><ref>{{Cite web|date=2021|title=Technical Note. Galvanic Isolation|url=https://www.isystem.com/files/content/downloads/documents/technical-notes/iSYSTEM_TN_Galvanic_Isolation.pdf#page=4|website=iSYSTEM|format=PDF|access-date=13 February 2022|archive-date=21 December 2021|archive-url=https://web.archive.org/web/20211221080208/https://www.isystem.com/files/content/downloads/documents/technical-notes/iSYSTEM_TN_Galvanic_Isolation.pdf#page=4|url-status=live}}</ref>

=== MIDI ===
The ''USB Device Class Definition for MIDI Devices'' transmits Music Instrument Digital Interface ([[MIDI]]) music data over USB.<ref>{{cite web |url=https://www.usb.org/sites/default/files/midi10.pdf |title=Universal Serial Bus Device Class Definition for MIDI Devices |website=usb.org |date=1 November 1999 |access-date=21 July 2021 |archive-date=2 November 2021 |archive-url=https://web.archive.org/web/20211102080622/https://www.usb.org/sites/default/files/midi10.pdf |url-status=live}}</ref> The MIDI capability is extended to allow up to sixteen simultaneous ''virtual MIDI cables'', each of which can carry the usual MIDI sixteen channels and clocks.

USB is competitive for low-cost and physically adjacent devices. However, Power over Ethernet and the [[MIDI]] plug standard have an advantage in high-end devices that may have long cables. USB can cause [[ground loop (electricity)|ground loop]] problems between equipment, because it connects ground references on both transceivers. By contrast, the MIDI plug standard and [[Ethernet]] have built-in isolation to {{gaps|500|V}} or more.

=== eSATA/eSATAp ===
The [[eSATA]] connector is a more robust [[SATA]] connector, intended for connection to external hard drives and SSDs. eSATA's transfer rate (up to 6&nbsp;Gbit/s) is similar to that of USB&nbsp;3.0 (up to 5&nbsp;Gbit/s) and USB&nbsp;3.1 (up to 10&nbsp;Gbit/s). A device connected by eSATA appears as an ordinary SATA device, giving both full performance and full compatibility associated with internal drives.

eSATA does not supply power to external devices. This is an increasing disadvantage compared to USB. Even though USB&nbsp;3.0's 4.5&nbsp;W is sometimes insufficient to power external hard drives, technology is advancing, and external drives gradually need less power, diminishing the eSATA advantage. [[eSATAp]] (power over eSATA, a.k.a. ESATA/USB) is a connector introduced in 2009 that supplies power to attached devices using a new, backward compatible, connector. On a notebook eSATAp usually supplies only 5&nbsp;V to power a 2.5-inch HDD/SSD; on a desktop workstation it can additionally supply 12&nbsp;V to power larger devices including 3.5-inch HDD/SSD and 5.25-inch optical drives.

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

eSATA, like USB, supports [[hot plugging]], although this might be limited by OS drivers and device firmware.

=== Thunderbolt ===
{{Main|Thunderbolt (interface)}}
Thunderbolt combines [[PCI Express]] and [[DisplayPort]] into a new serial data interface. Original Thunderbolt implementations have two channels, each with a transfer speed of 10&nbsp;Gbit/s, resulting in an aggregate unidirectional bandwidth of 20&nbsp;Gbit/s.<ref>{{cite web |url=https://thunderbolttechnology.net/tech/how-it-works |title=How Thunderbolt Technology Works: Thunderbolt Technology Community |website=ThunderboltTechnology.net |access-date=22 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20140210063142/https://thunderbolttechnology.net/tech/how-it-works |archive-date=10 February 2014 }}</ref>

[[Thunderbolt 2]] uses link aggregation to combine the two 10&nbsp;Gbit/s channels into one bidirectional 20&nbsp;Gbit/s channel.<ref>{{cite web |title=What you need to know about Thunderbolt 2 |url=https://www.macworld.com/article/222636/what-you-need-to-know-about-thunderbolt-2.html#:~:text=What%20is%20Thunderbolt%202%3F,20%20Gbps%20bi%2Ddirectional%20channel. |first=Jim |last=Galbraith |date=2 January 2014 |access-date=18 June 2021 |website=Macworld |publisher=IDG Communications, Inc. |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624202741/https://www.macworld.com/article/222636/what-you-need-to-know-about-thunderbolt-2.html#:~:text=What%20is%20Thunderbolt%202%3F,20%20Gbps%20bi%2Ddirectional%20channel. |url-status=live }}</ref>

[[Thunderbolt 3]] and [[Thunderbolt 4]] use [[USB-C]].<ref>{{cite web|url=https://www.cnet.com/news/thunderbolt-3-and-usb-type-c-join-forces-for-one-port-to-rule-them-all/|title=One port to rule them all: Thunderbolt&nbsp;3 and USB Type-C join forces|archive-url=https://web.archive.org/web/20150602195337/http://www.cnet.com/news/thunderbolt-3-and-usb-type-c-join-forces-for-one-port-to-rule-them-all/|archive-date=2 June 2015|url-status=live|access-date=2 June 2015}}</ref><ref>{{cite web |url=https://www.engadget.com/2015/06/02/thunderbolt-3-usb-c/ |title=Thunderbolt&nbsp;3 is twice as fast and uses reversible USB-C |date=2 June 2015 |access-date=2 June 2015 |url-status=live |archive-url=https://web.archive.org/web/20150603000428/http://www.engadget.com/2015/06/02/thunderbolt-3-usb-c/ |archive-date=3 June 2015  }}</ref><ref>{{cite web |url=https://arstechnica.com/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/ |title=Thunderbolt&nbsp;3 embraces USB Type-C connector, doubles bandwidth to 40&nbsp;Gbps |author=Sebastian Anthony |date=2 June 2015|website=Ars Technica |access-date=2 June 2015 |url-status=live |archive-url=https://web.archive.org/web/20150609183247/https://arstechnica.com/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/ |archive-date=9 June 2015  }}</ref> Thunderbolt&nbsp;3 has two physical 20&nbsp;Gbit/s bi-directional channels, aggregated to appear as a single logical 40&nbsp;Gbit/s bi-directional channel. Thunderbolt 3 controllers can incorporate a USB&nbsp;3.1 Gen&nbsp;2 controller to provide compatibility with USB devices. They are also capable of providing DisplayPort Alternate Mode as well as DisplayPort over USB4 Fabric, making the function of a Thunderbolt&nbsp;3 port a superset of that of a USB&nbsp;3.1 Gen&nbsp;2 port.

DisplayPort Alternate Mode 2.0: USB4 (requiring USB-C) requires that hubs support DisplayPort 2.0 over a USB-C Alternate Mode. DisplayPort 2.0 can support 8K resolution at 60&nbsp;Hz with HDR10 color.<ref name="displayport">{{cite web |title=New DisplayPort spec enables 16K video over USB-C |url=https://www.theverge.com/2020/4/30/21242445/vesa-displayport-alt-mode-2-0-usb-4-4k-144hz-hdr-8k-16k-displays |first=Jon |last=Porter |date=30 April 2020 |access-date=18 June 2021 |website=The Verge |publisher=Vox Media, LLC |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415051447/https://www.theverge.com/2020/4/30/21242445/vesa-displayport-alt-mode-2-0-usb-4-4k-144hz-hdr-8k-16k-displays |url-status=live }}</ref> DisplayPort 2.0 can use up to 80&nbsp;Gbit/s, which is double the amount available to USB data, because it sends all the data in one direction (to the monitor) and can thus use all eight data wires at once.<ref name="displayport"/>

After the specification was made royalty-free and custodianship of the Thunderbolt protocol was transferred from Intel to the USB Implementers Forum, Thunderbolt 3 has been effectively implemented in the USB4 specification – with compatibility with Thunderbolt 3 optional but encouraged for USB4 products.<ref>{{cite web|title=USB4 Thunderbolt3 Compatibility Requirements Specification|url=https://www.usb.org/sites/default/files/USB4%E2%84%A2%20Thunderbolt3%E2%84%A2%20Compatibility%20Requirements%20Specification%20Rev%201.0%20-%2020210129_0.pdf|date=January 2021|access-date=1 January 2021|website=USB|publisher= USB Implementers Forum |archive-date=19 October 2021|archive-url=https://web.archive.org/web/20211019074211/https://usb.org/sites/default/files/USB4%E2%84%A2%20Thunderbolt3%E2%84%A2%20Compatibility%20Requirements%20Specification%20Rev%201.0%20-%2020210129_0.pdf|url-status=live}}</ref>