As Corey said, administrative computers in switching centers ran Unix, but the call-processing machines ran an unrelated operating system. The Unix lab did influence that operating system. Bob Morris instigated, and Joe Condon, Lee McMahon, Ken Thompson and others built TPC (the phone company), a switching system controlled by a PDP-11. This system actually ran the phones in CS Research for several years. ESS5 adopted some of TPC's architecture, though none of its code. Doug