Ronald Natalie scripsit:

> More strictly, UNIX doesn’t have “type” in a file.   They’re
> just a bunch of bytes.   It’s up to whoever is making the file to
> decide if the name conveys that information or a magic number does.

True.  On the IBM PC AT I mentioned earlier, I needed a number of binary
file formats, as it was clear that ASCII-binary conversion was too slow
for the purpose.  (Probably not true even then, but what did I know?)
So I duly assigned 16-bit magic numbers for each file format, and
#define'd them in the code.  Where did the magic come from?  They were
RAD50 encodings of three-letter file codes!

Johnny Billquist scripsit:

> On the PDP-8, you sometimes saw @ used as a prefix character in
> SIXBIT. So you'd use @M to get a CR, and @J for an LF, and @@ would
> mark the end of the string. But not for filenames. But in code, since
> you sometimes used SIXBIT for string constants as well.

Yes, I think that's what I was half-remembering.

-- 
John Cowan          http://www.ccil.org/~cowan        cowan at ccil.org
You are a child of the universe no less than the trees and all other acyclic
graphs; you have a right to be here.  --DeXiderata by Sean McGrath