Two Stop Bits | It was clearly a very popular machine with users; there was no real business cas...

KODust 49 days ago | parent

It was clearly a very popular machine with users; there was no real business case for producing clones, and yet there were no less than 3 companies that attempted PDP-10 clones -- one of them in the mid 1990's! -- in addition to the one-off clone at Xerox PARC. Ritche and Thompson wanted one at Bell Labs to develop early Unix (and settled for a PDP-11 instead). And DEC threw it completely away in 1983 by stopping development on the successor machines. They could have done one at least more generation, and it would have been at least a modest success and kept some of those users on board the DEC train.

ozymandiax 49 days ago
You have to wonder, what would modern CPUs look like if Thompson and Ritchie had implemented unix on a PDP-10 and that had become the 'normal' for CPUs...
- larsbrinkhoff 46 days ago
  It's not a given that a "Unix" on a PDP-10 would have taken off like the PDP-11 version did. I believe the success of Unix was partially because it ran on an inexpensive and wildly popular mini.
  Even as a PDP-10 fan, I have to admit that the PDP-10 was not exactly the wave of the future during the 1970s. It had a decent niche and a steadfast following, but sooner or later it would have disappeared in favor of 8-bit byte addressed computers.
  - KODust 45 days ago
    Real alternative history territory here, but one path possible path is that it still have been attractive enough to port to the VAX, and we'd have ended up in roughly same place. Lots of handwaving and assumptions, of course.
    I'm not sure Unix failing to take off would have been bad. It would certainly be a different world.
    - larsbrinkhoff 45 days ago
      Some random thoughts. Writing a timesharing system for a computer with a 16-bit address space forced the Unix philosophy with many small single-purpose programs passing data between them. A timesharing system on a PDP-10 wouldn't have this constraint, and may well not have developed the Unix philosophy. Maybe that would have removed some of the appeal of "Unix-10".
      Second, the VAX grew from the PDP-11 as a 32-bit addressing extension. So porting from the PDP-11 to the VAX is rather natural and easy. In contrast, the PDP-10 is rather different from both the PDP-11 and VAX. Programs written in assembly language will not port over. If Bell labs would have developed a C language for the PDP-10, I wager it would have looked different and not have become popular in an 8-bit byte world.
      - bmonkey325 44 days ago
        Some forget that Unix started out on the pdp-7 which was 18-bit words so in some ways the architecture argument doesn’t really hold up. I think it’s more what machine were they could access.
        https://linfo.org/pdp-7.html#:~:text=The%20PDP-7%20was%20a%2....
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        KODust 44 days ago
        Yes, this is the thing -- it's clear that Ken Thompson valued simplicity, one reason being that he and a couple of other people could maintain the entire thing without a large support organization. Whether that would have survived the PDP-10, I'm not sure. But I suspect it would have have been recognizably Unix.
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        larsbrinkhoff 44 days ago
        PDP-7 Unix is even more cramped with a 12-bit address space per process.
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        bmonkey325 44 days ago
        This version of Unix was all assembly code and not portable. Once they could move to a better machine I think they realized they didn’t want to write it again in assembly because porting could be difficult.
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        larsbrinkhoff 44 days ago
        My argument is that the PDP-7 and PDP-11 possibly forced the Unix philosophy. I don't understand what you are arguing.
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    - bmonkey325 45 days ago
      Is this the parallel universe where Mac won and Windows faded into obscurity. Amiga took over gaming and PlayStation and XBox never happened ? .
      Also. Steve Jobs lives…..
      - KODust 44 days ago
        Dave Cutler stayed at DEC, shipped popular workstations built with PRISM chips, Microsoft and IBM kissed and made up and we're all using Windows derived from OS/2 w/Presentation Manager today.
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        bmonkey325 44 days ago
        Put that way. In the hear and now, I realize we are in the darkest timeline.
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larsbrinkhoff 46 days ago
Foonly and Systems Concepts seemed to have a decent business, although their customer base was largely restricted to one each: Tymshare and Compuserve, respectively.
The PARC clones were two-off.
KODust 48 days ago
also http://www.fpgaretrocomputing.org/pdp10x/