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Grex Systems Item 104: The TOPS-20 item
Entered by cross on Thu Apr 2 00:51:34 UTC 2009:

This item is about the TOPS-20 operating system, once common on Digital
Equipment Corporation (DEC) DECsystem-20 mainframes.  Such machines were
36-bit, word-oriented machines that used the PDP-10 instruction set and
paged, virtual memory.  TOPS-20, often referred to as TWENEX, was an
outgrowth of the earlier TENEX system and was considered the most "advanced"
of the several timesharing operating systems that ran on the PDP-10 series
of computers.

8 responses total.

#1 of 8 by remmers on Thu Apr 2 16:47:22 2009:

I had vast experience with TOPS-10, the predecessor to TOPS-20, in the
1970s and 1980s when it was the OS for the academic mainframe at my
university.  My experience with TOPS-20 is confined to a project I
worked on for a few months in the late 1970s while consulting for the
Ford Motor Company.  I recall that the command-line interface had a "tab
completion" feature that was a bit ahead of its time - you could type
the first few characters of a command and fill in the rest by hitting
the tab key.  Seems commonplace now, but I don't think the feature
showed up in Unix shells until several years later.

A brief TOPS-20 history is here:  http://www.answers.com/topic/tops-20

#2 of 8 by cross on Sat Apr 4 02:21:24 2009:

I prefer the "normal" wikipedia article; it's formatted better.

Interestingly, one can still run TOPS-20 (and TOPS-10, and ITS, another
PDP-10 operating system).  Check out: http://panda.com/tops-20/
Marc Crispin (yes, that Marc Crispin) still hosts a downloadable,
mostly-pre-configured TOPS-20 image suitable for use with the KLH10
PDP-10 simulator.  It will even do TCP/IP.  I recently brought this
up elsewhere and it caused something of a local stir.

#3 of 8 by cross on Mon May 18 04:38:42 2009:

The main reason that I posted this item is that I still consider
TOPS-20 to be an incredibly rich computing environment, often
rivalling what we see today: the Unix shell is pretty primitive as
a command interperter, and despite the fact that newer shells have
dressed the system up somewhat, it still has many odd features that
we tend to take for granted and accept without question now.  The
TOPS-20 command interface is, conceptually at least, probably closer
in spirit to the Windows PowerShell than to, say, tcsh.

Often, we end up using systems that are heavily influenced by other
systems without even really realizing it; for instance, the design
of the Unix 'mmap()' interface is largely modelled on TOPS-20.  Yet,
how many of us have used the system that the thing is based on?  I
submit that it is good to go back and look at the primary sources
for purposes of comparison and contrast with our present-day systems;
what we discover in doing so often surprises us and makes us wonder
at how clunky and generally crude today's systems are.

Here's a paper on TENEX, the immediate pre-cursor to TOPS-20:
http://www.opost.com/dlm/tenex/tenex72.txt

#4 of 8 by dtk on Sun Jan 6 23:27:57 2013:

For those of you familiar with Cisco's IOS interactive environment, you 
can thank (or blame) Twenex for a lot of that. The idiom of "enable" to 
raise privileges and "disable" to return to normal use mode is a Twenex-
ism. Tab-completion came to IOS from Twenex, as well.  -DTK

#5 of 8 by cross on Mon Jan 7 02:00:25 2013:

Funny you should revive this thread, David.  I'm sad to report that Mark
Crispin is terminally ill and in hospice; for now, the panda.com site seems
to be down.

#6 of 8 by dtk on Mon Jan 7 05:20:48 2013:

I am sorry to hear. I wish for his family comfort in his memory in this
time  of grieving and after.  -DTK

#7 of 8 by papa on Mon Feb 13 05:49:09 2017:

Long Live TWENEX! www.twenex.org

#8 of 8 by cunnings on Fri May 26 00:25:28 2017:

I'm still enjoying Panda TOPS-20 running at home on an RPi3... accounts
are also available on the TOAD-1 machine at livingcomputermuseum.org

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