The "loop and a half"
bartc
bc at freeuk.com
Mon Oct 9 06:43:16 EDT 2017
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.]
--
bartc
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