ZX Interface 1

Originally intended as a local area network interface for use in school classrooms, it was revised before launch to also act as the controller for up to eight ZX Microdrive high-speed tape-loop cartridge drives.

At hardware level it was fundamentally a voltage adaptor, the serial protocol being implemented in software by bit-banging.

As this became an official standard, other developers quickly used this mechanism to create language extensions to Sinclair BASIC.

[1] These aimed to improve ZX Microdrive cartridge formatting and access time, printing functions via the RS-232 interface, and other bugs in the firmware held in the device's internal 8K ROM.

Data could be sent or received at 100 kbit/s either to or from a numbered workstation, or broadcast to all nodes, allowing one machine to act as a server.