github.com/Microsoft/MS-DOS/tr

"The user manual contains some significant errors. Most of these are due to last minute changes to achieve a greater degree of compatibility with IBM's implementation of MS-DOS (PC DOS). This includes the use
of "\" instead of "/" as the path separator, and "/" instead of "-"
as the switch character."

it's always kind of interesting when you encounter a fossil trace of someone's Giant Mistake as it happened.

@brennen The weird thing about this is that "/" was the switch character on RT-11, which CP/M imitated (including using "/" as the switch character in PIP.COM), and MS-DOS 1.0 was a carbon copy of CP/M (though I don't remember if it had PIP).

@kragen @brennen There's a reason why MS-DOS 2.0 specifically was planned to use / as the path separator and - as the switch, though.

MS-DOS 1.x was absolutely a CP/M clone, but MS-DOS 2.0 was intended to be something entirely different - the eventual goal was to turn MS-DOS into a single-user, single-tasking Unixlike, with Xenix binary compatibility (much like the goal of Heinz Lycklama's Version 6 Unix-derived LSX).

Obviously things did not ultimately go that direction, but a fair amount of Unix semantics made it into MS-DOS as a result anyway.

@bhtooefr @kragen @brennen
This is something I hadn't heard!

I knew that directories were one of several features Microsoft added that were taken from UNIX, & that Microsoft's status as a UNIX vendor at the time was related, but I was unaware of any plan to make them actually binary-compatible! That would have been a very interesting system.

Was Xenix even using 16 bit words? Unix on micros usually had 18-bit words, right?

@enkiv2@eldritch.cafe @bhtooefr@cathoderay.tube @kragen@nerdculture.de @brennen@mastodon.social Unix on micros and minis used 16-bit words, afaik there's actually never been a port of UNIX to an architecture that uses a non power of two word size but I could be wrong about that.

@ACE_Recliner @brennen @bhtooefr @kragen
Huh, that strikes me as odd. I was pretty sure that earlier PDP models than the one UNIX was developed on had 18 bit words, & it seems a little weird to change the word length to something without common factors. But, that was early days & maybe digital didn't care the way intel did.

I recall that, somehow, MINIX had 9-bit *bytes*. (At least, a friend who was porting MINIX to modern hardware said that & I don't think he was screwing with me.)

@enkiv2 @kragen @brennen @ACE_Recliner The PDPs date back to the era when each new model got a new architecture...

The PDP-11 was the first (and last) of the 16-bit PDP family (with the VAX being a 32-bit continuation of the PDP-11 architecture).

There were also 18-bit, 12-bit, and 36-bit PDPs - Unix originally targeted the PDP-7, one of the 18-bit PDPs, but was quickly ported to PDP-11.

@bhtooefr
@brennen @kragen @enkiv2

[One of these days the VAX cluster my officemate still has running will fully and finally die, and my office will suddenly be a *lot* quieter!]

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@keithzg @enkiv2 @kragen @brennen @bhtooefr this also helps explain why all the 1970s RAM ICs are odd-by-modern-standards 1 or 4 bit.

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