From: utzoo!decvax!aps
Newsgroups: net.unix-wizards
Title: 4.1bsd mystery
Article-I.D.: decvax.470
Posted: Thu Apr 14 18:31:41 1983
Received: Mon Apr 18 21:47:30 1983

Mycroft Holmes or qubiz!msc (which ever) is correct in that the name
comet was given to the 11/750 project (star->780, and nebula->730).
The problem was that the doprint was using the movtuc (Move translated
until character) to move UNIX null terminated strings instead of the
"normal" VAX and/or VMS counted strings.  The string lengths were set to
the maximum for both source and destination, and the "escape" character
was set to the null character.  The table was just an identity table,
translating a charater into itself.  The architecture manual (even the
first manuals) stated that if the source string and destination string
overlapped (and their starting addresses were not equal which allowed
translation in place), the result would be unpredictable.  The VAX-11/780
actually did not really care.  The MOVTUC was implemented in a straight
forward manner.  The 750 however, performed some "optimizations" which
required adherence to the limitation stated in the books.  So, it didn't
work on the 750.  Hence Joy's (or Shannon's) comment about the wonderful
comet.

The comet went on to be one of the favorite machines of the DEC UNIX
Engineering Group ...

		Armando.