&quot;The most important role for UNIX is to provide a file system.&quot;<p>I looked up TGM which is mentioned in this manual (TGML).  Apparently this was what Thompson used to write the B compiler.<p>Anyway, I ended up on the Multicians site.  Some online accounts of computing history suggest UNIX was an alternative to the Multics project.<p>On the Multicians site it suggests Multics had a very different concept of &quot;files&quot;, which could also be &quot;segments&quot;.  There was apparently potential ambiguity regarding the term &quot;file&quot;.<p>Here&#x27;s my question for anyone who was there:<p>Today we often see the phrase &quot;Everything is a file&quot; being cited when introducing people to UNIX.  But I have never seen anyone attempt to explain why.  What was the context in the 1970&#x27;s?<p>Was the UNIX notion of &quot;files&quot; a reaction to the approach taken by Multics?<p>Again, this early manual says: &quot;The most important role for UNIX is to provide a file system.&quot;