When did DECNET first appear? Mid-1970s, depending on which version ("Phase") you consider to be "DECnet". I'm sure someone will provide a more specific date. using what means to connect each system. Point to point serial (note that doesn't mean RS-232!) links (rarely parallel) using various means for the actual physical connection. DECnet definitely predates Ethernet by many years, if that's your point. Bob ANF10!