An AUI connector is a 15-pin D-connector. It has a sliding clip in place of the thumbscrews normally found on a D-connector to hold two connectors together. This clip permits the MAU and MAC to be directly attached to one another even when their size and shape would preclude the use of thumbscrews.
AUI connectors became rarer from the early 1990s. This was because it became more common for computers and hubs to incorporate the MAU, particularly as the 10baseT standard became more common and use of 10BASE-5 (thicknet) and 10BASE-2 (thinnet) declined. The electrical AUI connection was still present inside the equipment. By the mid-1990s AUI had all but disappeared as fast ethernet, which has no direct equivalent of AUI, became more common. Gigabit ethernet and 10 gigabit ethernet have respectively the GBIC and XAUI standards which are equivalent to AUI.
|1||control in circuit shield|
|2||control in circuit A|
|3||data out circuit A|
|4||data in circuit shield|
|5||data in circuit A|
|8||control out circuit shield|
|9||control in circuit B|
|10||data out circuit B|
|11||data out circuit shield|
|12||data in circuit B|
An AUI cable may be up to 50 metres long, although frequently the cable is omitted altogether and the MAU and MAC are directly attached to one another.
A modified form using a smaller connector called the AAUI was used on Apple Macintosh computers in the early 1990s.