"Communication files" in the Dartmouth Time Sharing System have been cited as a predecesssor of Unix pipes, although we at Bell Labs were unaware of the DTSS feature when pipes were first implemented. In fact, communication files more directly foreshadow Plan 9 than they do Unix.

 Unlike Unix processes, which need not be aware that they are talking to pipes, the process at one end of a communication file, designated as "master", must be aware that it  is a communication file. The master end controls the semantics of reads, writes and seeks(!) issued at the other end. Because of this asymmetry, a communication file cannnot serve as a pipe between pairs of unprepared processes. A pipe could be simulated in DTSS by a master process that relays flow between communications files connected to arbitrary end processes, but that seems never to have been done. 

Communication files are a closer antecedent to Plan 9. A master process's controls  correspond to the part of Plan 9's foundational 9P protocol that handles open files. Though  I don't think there's an actual ancestral connection, this likeness strengthens DTSS's claim to fame and extends their lead to nearly a quarter century.

Linux has adopted surface features of Plan 9 like union directories, append-only files and system data access via file interfaces. Meanwhile Plan 9's revolutionary realization of what Vic Vyssotsky called distributable computing has not caught on. In distributable computing, the physical location of processes does not affect their logical interaction. In today's distributed computing, though, there is a world of difference between how processes interact remotely and locally. When will the crevasse between the possible and the normal be bridged?

Doug

Having recently read about the playful literary consortium, Oulipo, I am reminded of their term for little-known antecedents of their revolutionary works: "anticipatory plagiarism".