Raps cane on floor.
It's probably an "end-of-file" sentinel because 'Z' is the last letter
of the alphabet. I suspect it comes from MIT. Unix, developed at a
telephone company, uses \x4, which was, in fact, the ASCII in-band
end-of-transmission code and would disconnect a teletype.
Does this qualify me for the dinosaur award?
R Fritz
On 2009-01-14 07:15:33 -0800, Mel <mwil...@the-wire.com> said:
Steve Holden wrote:
Unknown wrote:
On 2009-01-12, John Machin <sjmac...@lexicon.net> wrote:
I didn't think your question was stupid. Stupid was (a) CP/M recording
file size as number of 128-byte sectors, forcing the use of an in-band
EOF marker for text files (b) MS continuing to regard Ctrl-Z as an EOF
decades after people stopped writing Ctrl-Z at the end of text files.
I believe that "feature" was inherited by CP/M from DEC OSes
(RSX-11 or RSTS-11). AFAICT, all of CP/M's file I/O API
(including the FCB) was lifted almost directly from DEC's
PDP-11 stuff, which probably copied it from PDP-8 stuff.
Perhaps in the early 60's somebody at DEC had a reason. The
really interesting thing is that we're still suffering because
of it 40+ years later.
I suspect this is probably a leftover from some paper tape data formats,
when it was easier to detect the end of a file with a sentinel byte than
it was to detect run-off as end of file. It could easily date back to
the PDP-8.
Perhaps, although in ASCII it's the SUB symbol: "A control character that is
used in the place of a character that is recognized to be invalid or in
error or that cannot be represented on a given device." [Wikipedia]. There
were other codes defined for End-of-Text and File-Separator. Unless the
protocol were one of DEC's own. The fact that it's
Ctrl-last-letter-of-the-alphabet makes me suspect that it was picked in a
pretty informal way.
Mel.
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