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The "loop and a half"

Grant Edwards grant.b.edwards at gmail.com
Mon Oct 9 10:16:49 EDT 2017 
On 2017-10-09, Gregory Ewing <greg.ewing at canterbury.ac.nz> 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.

A "feature" that CP/M copied almost verbatim.  If you looked at the
CP/M FCB (file-control-block) structure it looked almost identical to
that used by early DEC OSes.  DOS then copied CP/M's file i/o scheme
even more exactly than CP/M had copied DEC.  It was years later than
DOS finally copied some Unix features like nested directories, opening
files via path strings, etc.

-- 
Grant Edwards               grant.b.edwards        Yow! Do you think the
                                  at               "Monkees" should get gas on
                              gmail.com            odd or even days?
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