From:	Jerry Avins <jxyzavins AT erols DOT com>
Newsgroups:	comp.os.msdos.djgpp,comp.os.cpm,alt.folklore.computers
Subject:	Re: EOF char. (Was C++ and RHIDE)
Date:	Mon, 06 Jul 1998 18:45:55 -0400
Organization:	The Hectic Eclectic
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Alan Bowler wrote:
> 
> In article <359FFF58 DOT 71CE272E AT alcyone DOT com> Erik Max Francis <max AT alcyone DOT com> writes:
> >Luc Van der Veken wrote:
> >
> >> What exact character would be used in the papertape days to
> >> signal the end of a tape? Decennia ago I used them, but I don't
> >> remember.
> >>
> >> CTRL/Z - ETX (CTRL/C) - EOT (CTRL/D) - EM (CTRL/Y)?
> >>
> >> Or more than one, platform-dependent?
> >
> >EOT (0x04, ^D) is the "correct" one from the ASCII standard, since it
> >stands for "end of transmission."  This is used (almost?) universally on
> >Unix systems,
> 
> That does not make it correct.  EOT had a particular function.
> It powered down the teletype to a standby state.  The motor would
> stop turning, and so on real teletypes that mechanically did the
> serial decode this meant that the teletype could not even interpret
> characters on the line.  The other end would wake up the teletype
> (start the motor running again) by sending a "long break"

On the big ASR TTY (model 30?) with a built-in modem, ^D would hang up
the phone. Shutting down the distributer motor would have been the
current-loop equivalent, and the "long break", created by holding down
the <break> key, had the current-loop effect of dialing in.
> 
Up above ^Z, there is a whole group of separators, RS (record), FS
(file), GS (group), etc., up to one sometimes called "word separator"
but more often, <space>. It is not in the format effector group (CR, LF,
HT, VT, BS), nor is it in the first two "sticks", so I don't call
<space> a control character at all.
 
> The "correct" choice for end of file, was File Separator (FS,
> control-backslash), but Gcos is the only system I know that used that.
> 
> Generally paper tape stuff didn't much use "end of file".
> A tape would be prepared with a set of chunks each ended by
> X-OFF (DC3, ctrl-S).  The machine would send out X-ON (DC1 ctrl-Q)
> to start the paper tape reader going, and the reader would stop
> when it read the next X-OFF.  Alternately, the machine use a timeout
> mechanism to decide when there was no more paper tape.

-- 
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"I view the progress of science as ... the slow erosion of the
 tendency to dichotomize."                    Barbara Smuts, U. Mich.
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