On 09/10/2017 06:15, Gregory Ewing wrote:
Grant Edwards wrote:
Which took it from RSX-11. Or probably more specifically from
FILES-11. I woldn't be surprised if the enineers at DEC got it from
somewhere else before that.
Quite possibly it goes back to the very earliest DEC OS
that had files, whatever that was.
The reason for it was that the file system only kept track
of file sizes in blocks, not bytes, so some way was needed
to mark the end of a text file part way through a block.
Ctrl-Z was just code 26 or [what I've always called] ETX or end-of-text.
I'd used DEC quite a bit (including rsx-11m) but only became aware of
ETX when using CP/M. (Where it had a annoying habit, IIRC, of copying
files in text mode so that it stopped at the first ETX byte.)
And actually, until recently, I added ETX (followed by 0 for good
measure) as a sentinel in a function reading a file into a block of
memory (now I just use 0 for that purpose).
But I don't consider that these internal uses, some of which are
archaic, belong in a user interface.
[Looking it up now, actual ETX is code 3, or Ctrl-C, and EOT is code 4.
So how 26 - apparently code SUB, whatever that means - ended up being
used to mark the end of text files, I don't know.]
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bartc
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