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As described in this question, Multics used > as the separator between components in pathnames, and < as a parent directory indicator in relative paths.

However, an early paper describing the implementation of the Multics filesystem uses : instead (and provides no indication of how parent directories were referenced). My understanding is that this paper describes the state of the Multics implementation as of "phase 0.5", which was a simulation of components of Multics running under an emulator on a GE635 so that work could begin before the actual GE645 hardware was ready. This work was completed in March 1967, and at some point after that work on the actual hardware begun.

The new syntax had been adopted by the time the system command language was described for the programmer's reference in October 1968.

Is there any available documentation as to when and why this change was made?

(Motivation: it may be interesting to know, in light of this question, how long the '>' convention had been in use at the time Bell Labs abandoned the Multics project)

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    Given how compartmentalized Multics was it's possible that the team designing the filesystem used one notation and the team responsible for implementing it used another. – Alex Hajnal Jul 17 '18 at 1:11
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    It’s also important to note that the file system paper is a general specification, it doesn’t describe the implementation of the Multics file system. – Stephen Kitt Jul 18 '18 at 13:06
  • The answer may lie in sections BE.10 and BG of the MSPM. I checked The Multics system; an examination of its structure but didn’t find anything relevant. – Stephen Kitt Jul 27 '18 at 11:56
  • As I remember, it was in use by the summer 1972. How about asking someone from the Multics team? – cmm Jul 17 '19 at 1:09
  • If was definitely in use in 1972 and some time before that, as it is mentioned in E.I.Organick's book (The Multics system: an Examination of its structure) published in 1972: "A path name, in the simplest sense, is a list of the node names from the root to the branch (or link) inclusive. Elements of the list are separated, not by commas as you might expect, but by the “>” character" page 224. (And btw, always found the < > characters better suited for path separation than /, ../, using cwd <<< to go up 3 dirs... – e2-e4 Aug 25 '20 at 1:11

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