[TUHS] VFS prior to 1984

[Norman Wilson]

Reaching outside of UNIX, RSX/11 used external
supervisor-mode processes called ACPs (ancillary
control processes) to implement file systems.
I don't know exactly how they were plugged in,
but I do know they were pluggable, so their
interface must have constituted a file-system
switch of some sort.  RSX dates back into the
1970s.

At some point in the latter part of the 1980s,
Ralph Stamerjohn (a name instantly recognizable
in the 16-bit DEC software world) gave a DECUS
talk about implementing a remote file system
through ACPs: a stub ACP on the client exporting
RPCs over the network, a real one at the server
end.  I remember chatting with him about how
that did and didn't resemble the way pjw had
done it; interesting architectural comparison.

Norman Wilson
Toronto ON