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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