[3] Apple Computer's Apple Desktop Bus (ADB), introduced in the mid-1980s, allowed all sorts of low-speed devices like mice and keyboards to be daisy-chained into a single port on the computer, greatly reducing the number of ports needed, as well as the resulting cable clutter.
ADB was universal on the Macintosh line by the late 1980s, and offered a clear advantage over the profusion of standards being used on PCs.
[4] Development of USB began the next year, in 1994, and the consortium included a number of the members of the A.b group, notably DEC and Microsoft.
[5] A.b had a number of technical advantages over USB, which would not re-appear on that system until years later, and it was also easier and less expensive to implement.
They needed a standardized bus for communicating device abilities and status between monitors and computers, and selected I²C because it required only two pins; by re-using existing reserved pins in the standard VGA cable they could implement a complete A.b bus (including power).
A number of monitors with A.b connectors started appearing in the mid-1990s, notably those by NEC, but this was at about the same time USB was being heavily promoted and few devices were available to plug into them, mostly mice and keyboards.
The higher layers, namely the signaling and protocol issues, are already defined to be the same as Philips' Inter-Integrated Circuit (I²C) bus.
A single I²C/A.b controller chip would be used inside the machine, connected on the motherboard to internal devices like the clock and battery power monitor.