@Cadbury_Moose @sdarlington @BashStKid @cstross
These were not an Ethernet thing, though.
They had 4 or 8 RS232 ports on one side, and a single cable connection on the other to a specialized I/O expansion board that needed just one IRQ to the CPU, with a specialized device driver (or an entire custom version of the operating system) to mux/de-mux the data stream.