Editing Attachment Unit Interface (section)

[[File:AUI Connectors.jpg|thumb|AUI Connectors. The male connector (left) is on the MAU and the female connector (right) is on the DTE device (typically either a [[computer]] or an [[Ethernet hub]]). Note the sliding clip.]]
[[File:AUI connector on DEC EtherWorks LC (DE100).jpg|thumb|AUI Connector with numbered pins on the [[Digital Equipment Corporation|DEC]] EtherWorks LC (DE100) [[Ethernet]] controller. Note the [[jackposts]] (as opposed to a sliding clip).]]

The '''Attachment Unit Interface''' ('''AUI''') is a physical and logical interface defined in the [[IEEE 802.3]] standard (additionally published in [[Federal_Information_Processing_Standards|FIPS]] PUB 107) for [[10BASE5]] Ethernet<ref name="spec">{{cite web|title=Federal Information Processing Standards Publication: local area networks: baseband carrier sense multiple access with collision detection access method and physical layer specifications and link layer protocol|url=https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub107-Mar1985.pdf|publisher=American National Standard (doi:10.6028/NBS.FIPS.107)|access-date=3 October 2024}}</ref> and the earlier [[Ethernet#History|DIX standard]]. The physical interface consists of a 15-pin [[D-subminiature]] connector that links an [[Ethernet]] node's [[Physical layer#Physical signaling sublayer|physical signaling]] to the [[Medium Attachment Unit]] (MAU),<ref>IEEE 802.3 ''7. Physical Signaling (PLS) and Attachment Unit Interface (AUI) specifications''</ref> sometimes referred to as a [[transceiver]]. An AUI cable can extend up to {{convert|50|m|ft|abbr=off}}, though often the MAU and [[data terminal equipment]]'s (DTE) [[medium access controller]] (MAC) are directly connected, bypassing the need for a cable. In Ethernet implementations where the DTE and MAU are combined, the AUI is typically omitted.

The IEEE 802.3 specification officially defines the AUI as an interconnect between a DTE and the MAU. However, devices like the [[Digital Equipment Corporation|DEC]] [[Digital Ethernet Local Network Interconnect]] (DELNI) provided hub-like functionality using AUI-compatible connectors.<ref>https://www.zx.net.nz/computers/dec/networks/DELNI/</ref><ref>https://vt100.net/mirror/hcps/delnitm1.pdf</ref> Additionally, under certain conditions, it was possible to directly connect two AUI devices without the need for transceivers using a [[crossover cable]].<ref>https://serverfault.com/questions/375782/is-it-possible-to-cross-connect-two-aui-ports-without-transceivers</ref>

AUI connectors became increasingly rare in the early 1990s as computers and hubs directly integrated the MAU, especially with the rising adoption of the [[10BASE-T]] standard. This shift led to the decline of [[10BASE5]] (thicknet) and [[10BASE2]] (thinnet) which made use of the interface.<ref>{{Cite web |url=https://www.mattmillman.com/projects/usbaui/ |title=Archived copy |access-date=2024-10-02 |archive-date=2024-08-28 |archive-url=https://web.archive.org/web/20240828194459/https://www.mattmillman.com/projects/usbaui/ |url-status=live }}</ref><ref>{{cite web | url=https://servercloud.com/the-evolution-of-network-port-sizes-from-10base-t-to-100-gigabit-ethernet/ | title=The Evolution of Network Port Sizes: From 10BASE-T to 100 Gigabit Ethernet | date=June 2022 | access-date=2024-10-02 | archive-date=2024-06-14 | archive-url=https://web.archive.org/web/20240614184417/https://servercloud.com/the-evolution-of-network-port-sizes-from-10base-t-to-100-gigabit-ethernet/ | url-status=live }}</ref> The electrical AUI connection remained internally within equipment for some time.

With the introduction of [[Fast Ethernet]], the AUI interface became obsolete and was replaced by the [[Media Independent Interface]] (MII).<ref>[https://40gethernet.wordpress.com/2009/05/08/overview-of-the-xaui-xlaui-and-caui-part1/ Overview of the XAUI, XLAUI and CAUI: Part1] {{Webarchive|url=https://web.archive.org/web/20190517201905/https://40gethernet.wordpress.com/2009/05/08/overview-of-the-xaui-xlaui-and-caui-part1/ |date=2019-05-17 }}, ''"...the existing AUI was not suitable and it was replaced by the MII interface..."''</ref> Subsequent Ethernet standards, such as [[Gigabit Ethernet]] and [[10 Gigabit Ethernet]], introduced the [[GMII]] and [[XGMII]] interfaces, respectively. A 10 Gigabit Ethernet interface, known as [[XAUI]], was developed to extend the operational distance of XGMII and reduce the number of interface signals.

A smaller variant called the [[Apple Attachment Unit Interface]] (AAUI) was introduced on [[Apple Macintosh]] computers in 1991, and was phased out by 1998.<ref>{{cite web|last=Dan|first=Knight|title=Apple's AAUI Ethernet Connector|url=http://lowendmac.com/tech/aaui.html|access-date=13 February 2012|archive-date=26 March 2009|archive-url=https://web.archive.org/web/20090326062546/http://lowendmac.com/tech/aaui.html|url-status=live}}</ref>