== The origin of RCS (the version control system)

Let's start with the tweets:
> [[@johnregehr
> https://twitter.com/johnregehr/status/426830492294332416]]:
> quick! who remembers a revision control system before RCS?
>
> [[@thatcks
> https://twitter.com/thatcks/status/426836819972751360]]:
> SCCS. Bonus trivia: RCS exists because getting SCCS required paying
> AT&T extra money and universities don't have that.

[[I've mentioned this before in passing ../tech/ModernAgeGreatness]],
but I might as well tell the full story (or at least folklore) here.
The disclaimer is that this is the story as I heard it, not definitive
history. A lot of Unix history goes around as folklore, or went around
in the days when people were still passing Unix history around.

Version 7 Unix didn't ship with any version control system at all.
[[SCCS http://en.wikipedia.org/wiki/Source_Code_Control_System]],
the first Unix version control system, first started appearing in
in AT&T's [[PWB http://en.wikipedia.org/wiki/PWB/UNIX]]. PWB and
things unique to it were not covered by [[AT&T's generous V7
university source code licenses UnixUniversitySourceCode]]; where
you could get them at all (and I'm not sure outsiders could in any
form before System III) AT&T apparently wanted extra money for them.
Universities of course did not feel like paying extra money for
niceties and anyways they weren't using PWB, they were using V7 or
later BSD and so would have had to port anything they wanted from
PWB to BSD.  All of this meant that if you were using Unix at a
university in the late 1970s and early 1980s you could look wistfully
on SCCS from afar but you almost certainly could not get a copy.

Which is where [[RCS
http://en.wikipedia.org/wiki/Revision_Control_System]] comes
from. As the Wikipedia entry helpfully mentions, [[Walter Tichy
http://en.wikipedia.org/wiki/Walter_F._Tichy]] wrote the initial version
of RCS while at Purdue, where he had access to V7 and BSD but I assume
not PWB. As the folklore goes, he wanted version control, could not get
SCCS, and so wrote his own. As one did with Unix programs in an academic
environment at the time, he released it for general use. Since quite a
lot of universities were in a similar position of wanting some sort of
version control on their Unix systems but not having SCCS, it got widely
adopted.

[[As I mentioned before ../tech/ModernAgeGreatness]] RCS required
(V7) Unix source code (specifically for _diff_), which might strike
you as odd if Tichy wrote it from scratch. As I remember the story,
RCS required some additional _diff_ features and and in an early
1980s university environment with V7 and BSD source code the easiest
way for Tichy to get that was to modify the BSD _diff_ to support
what RCS needed.  The reason you can get RCS widely today is GNU
diff, which is both free and directly supports the features that
RCS needs without any patching.

(I think that one of the diff features RCS needed was a three-way diff.
I believe it may have also wanted a somewhat different format of diff
output, given GNU diff's _-n_ argument.)

(The [[official RCS home page
https://www.cs.purdue.edu/homes/trinkle/RCS/]] has some early RCS
papers online.)