the #1 expantion bus was the S-100 from the Apple II
The S-100 bus was introduced with the Altair and then cloned and used in many other early 8080- and Z80-based machines. I don't recall what bus the Apple II used, but, since the S-100 bus is basically just an externalized copy of the 8080 bus and the Apple II was a 6502-based machine, I serious doublt that it used the S-100 bus . . .
