[TUHS] DEC filenames (was: Command-line options)

Johnny Billquist bqt at update.uu.se
Sun Mar 27 06:30:08 AEST 2016

On 2016-03-26 20:43, Clem Cole<clemc at ccc.com> wrote:
> On Fri, Mar 25, 2016 at 11:09 PM, Charles Anthony <
> charles.unix.pro at gmail.com> wrote:
>> >And Dec's RADIX-50, packing 3 characters into 16 bits. (IIRC the origin of
>> >the 6.3 filenames. bit I can't document that.)
> ​Sort of.... before ASCII, DEC used a few other 5 bit codes that were
> around such as baudot​ (look at the PDP-1/4 etc and KSR 28). RAD50 was a
> natural scheme for storing file name and using bits efficiently.
> Which, of course, lead to the abomination of case folding - it's not a bug,
> it's a feature 😂
> RAD50 gave us the x.y file name form with the implied dot et al. 6.3 and
> later 8.3 were natural directions from that coding.   Using the .3 ext as a
> type tag of course followed that naturally given that's all that was stored
> in the disk "catalog."  [And CP/M and PC/MS-DOS inherit that scheme -
> including the case folding silliness even though by that time all keyboard
> were upper and lower case and they stored the files in 8 bits].

Some other people already mentioned this, but... - SIXBIT. DEC might 
have used baudot in the very early machines, but I would say that SIXBIT 
dominated here for a long time. We see it both in the PDP-8, but also 
the PDP-6 and its follow ons. RAD50 was the natural extension of SIXBIT 
on a machine that did not have a word size that was a multiple of 6.

The x.y filename, as well as the 6+3 pattern predate the PDP-11. I would 
say that in this area, the PDP-11 didn't come with anything new, but 
just made life more complicated.

OS/8 for sure only have 6+2 filenames, but still in the x.y form. 
TOPS-10 have, I think, 6+3. And the Monitor (I think that was the name 
for the PDP-6 OS) was, I think, also 6+3.
And it was all SIXBIT.

And SIXBIT also give you the case folding.

I say the PDP-11 complicated life just because DEC was already so much 
into having filenames stored more compact than normal text, and having a 
6+3 pattern, so they came up with R50, which fits the bill, but it's 
more headache than it was worth, if you ask me.
Since the PDP-11 have 8 bit bytes, it would have made much more sense to 
just store filenames as 8 bit bytes. It would have cost some more 
storage, but not that much. But it took time for DEC to realize that the 
space savings here were not really a good tradeoff. Old habits die hard, 
I guess.

By the way, RSX (and early VMS) actually use 9+3 filenames.

> UNIX of course, would put the "type" in the file itself (magic #) and force
> the storing of the dot, but removed the strict mapping of name and type.
> Having grown up in both systems, I see the value of each; but agree I think
> I find UNIX's scheme better and lot more flexible.

I think I agree on the point of having filenames in a free format. Not 
sure I really like storing the type in the file itself. So I'm sortof 
torn. Or rather, I would like to keep type separate from both.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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