That looks like an "Apple tax". The principle of the AUI port was that the three Ethernet connections (10Base5, 10Base2, 10BaseT) could all be used with a 'che

That looks like an "Apple tax". The principle of the AUI port was that the three Ethernet connections (10Base5, 10Base2, 10BaseT) could all be used with a 'cheap' change of "MAU" adapter. For 10Base5, it would have been impractical to have the thick cable brought right up to the computer. The 10Base5 MAU was relatively expensive, I see a card sold with it costing £50 more than the same card with a 10Base2 interface in a price list from 1993 [1]. I don't see a price for a 10BaseT interface alone, but it should be much cheaper — it's just a couple of low-pass filters and some isolation. Even back then I think these main components were sold as a single package ("chip"), so the 10BaseT MAU is two plugs, one "chip" and a couple of capacitors. Anyway, Acorn¹ computers were sold from around 1991 with an optional Ethernet card. Basic TCP/IP was included in ROM on the card, and it works fine between my Linux and Acorn computers. [1] https://chrisacorns.computinghistory.org.uk/docs/IntInt/II_PriceListFeb93.pdf https://chrisacorns.computinghistory.org.uk/docs/IntInt/II_P... ¹ Acorn as in "Acorn RISC Machine" → "Advanced RISC Machine" → the ARM chip in your phone.