I don't know if anyone would be interested in this, but it was the first time I bothered to read the man page of TCSH (ehm.. that is.. pull it up). I thought this was interesting and thought maybe someone else might be too :
THE T IN TCSH
In 1964, DEC produced the PDP-6. The PDP-10 was a later re-implementa-
tion. It was re-christened the DECsystem-10 in 1970 or so when DEC
brought out the second model, the KI10.
TENEX was created at Bolt, Beranek & Newman (a Cambridge, Massachusetts
think tank) in 1972 as an experiment in demand-paged virtual memory
operating systems. They built a new pager for the DEC PDP-10 and cre-
ated the OS to go with it. It was extremely successful in academia.
In 1975, DEC brought out a new model of the PDP-10, the KL10; they
intended to have only a version of TENEX, which they had licensed from
BBN, for the new box. They called their version TOPS-20 (their capi-
talization is trademarked). A lot of TOPS-10 users (`The OPerating
System for PDP-10') objected; thus DEC found themselves supporting two
incompatible systems on the same hardware--but then there were 6 on the
PDP-11!
TENEX, and TOPS-20 to version 3, had command completion via a user-
code-level subroutine library called ULTCMD. With version 3, DEC moved
all that capability and more into the monitor (`kernel' for you Unix
types), accessed by the COMND% JSYS (`Jump to SYStem' instruction, the
supervisor call mechanism [are my IBM roots also showing?]).
The creator of tcsh was impressed by this feature and several others of
TENEX and TOPS-20, and created a version of csh which mimicked them.
