AAUI

Apple Attachment Unit Interface (AAUI) is a mechanical re-design by Apple of the standard Attachment Unit Interface (AUI) used to connect Ethernet transceivers to computer equipment. AUI was popular in the era before the dominance of 10BASE-T networking that started in the early 1990s; AAUI was an attempt to make the connector much smaller and more user friendly.

AAUI was part of a system of Ethernet peripherals that tried to make connecting to Ethernet much easier. At the time, Ethernet systems usually were 10BASE2, also known as thinnet. Apple's system was called FriendlyNet. A FriendlyNet 10BASE2 system did not use BNC T-connectors or separate 50 Ω terminators. Instead of a single BNC connector that was inserted into a T-connector placed inline in the cable, the AAUI transceiver had two BNC connectors, one on each side to which the cables were attached. The transceiver would automatically terminate the network if a cable was not attached to one of the sides. Additionally, Apple 10BASE2 cables would terminate the network if no device was attached to them. Thus the number of mistakes that could be made hooking up a thinnet network was reduced considerably. Since any of these mistakes would disable the network in an area this was a significant improvement.

FriendlyNet equipment was quite expensive and even third-party AAUI transceivers were rather expensive. Because of this, Apple's computers, which were billed as having built-in Ethernet, were actually rather expensive to connect to Ethernet, perhaps adding as much as 10% to the total price of the computer system. Additionally, AAUI held no advantage for any system other than 10BASE2 and thus as 10BASE-T became ubiquitous it became impossible to justify the cost of an external transceiver at all. Apple eventually abandoned the system and sold off the name.

Macintosh Quadra, Centris, PowerBook 500, Duo Dock II (for PowerBook Duo) and early Power Macintoshes had an AAUI port, which requires an external transceiver. By the time AAUI was nearing the end of its life, an AAUI transceiver could cost as much or more than the cost of a low-cost Ethernet card on the PC—a disproportionate amount—as network cards for PCs did not become commodity items until the spread of broadband internet in the early 21st century. Later models included both an AAUI and modular connector port for directly connecting 10BASE-T; either could be used, but not both at the same time. AAUI connectors were also present on some Processor Direct Slot Ethernet adapter cards used in Macintosh LC and Performa machines. AAUI had disappeared by the late 1990s, when all new Apple machines, starting with the beige Power Macintosh G3 series, included only 10BASE-T.

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