TUHS

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Re: [TUHS] How to do differential/integral on a PDP-7, was: Space Travel

by Dave Horsfall

On Mon, 21 Oct 2019, Andrew Hume wrote: > the gt40??? oh my lord! good job i am en route to the bell labs 50th > anniversary. > its been a long time since i heard the name “Dave Horsfall”! Yep :-) Although now retired, I'm still active in Unix projects. -- Dave

5 years, 6 months

Re: [TUHS] Space Travel, was New: The Earliest UNIX Code

by Doug McIlroy

I was about to add a footnote to history about how the broad interests and collegiality of Bell Labs staff made Space Travel work, when I saw that Ken beat me to telling how he got help from another Turing Award winner. > while writing "space travel," > i could not get the space ship integration > around a planet to keep from either gaining or > losing energy due to floating point errors. > i asked dick hamming if he could help. after > a couple hours, he came back with a formula. > i tried it and it worked perfectly. it was some > weird simple double integration that self > corrected for fp round off. as near as i can > ascertain, the formula was never published > and no one i have asked (including me) has > been able to recreate it. If I remember correctly, the cause of Ken's difficulty was not roundoff error. It was discretization error in the integration formula--probably f(t+dt)=f(t)+f'(t)dt. Dick saw that the formula did not conserve energy and found an alternative that did.

5 years, 6 months

What was your "Aha, Unix!" moment?

by Warren Toomey

All, we had another dozen TUHS suscribers to the list overnight. Welcome. A reminder that we're here to discuss Unix Heritage, so I'll nudge you if the conversation goes a bit off-topic. So I'll kick off another thread. What was your "ahah" moment when you first saw that Unix was special, especially compared to the systems you'd previously used? Mine was: Oh, I can: + write a simple script + to edit a file on the fly + with no temporary files (a la pipes) + AND I can change the file suffix and the system won't stop me! I was using TOPS-20 beforehand. Cheers, Warren

5 years, 6 months

PDP-7 UNIX filesystem

by Angelo Papenhoff

DMR explained how PDP-7 UNIX was used in "The Evolution of the Unix Time-sharing System" but having played with it myself, I stumbled in a couple of cases and found it a bit awkward to use. Maybe someone (ken and doug?) can shed some light on "elaborate set of conventions" that dmr mentioned. My questions are these: you cannot execute a program if you're in a directory you can't write into. I asked Warren about this when I first tried pdp7 unix and he explained it to me: the shell creates a link to the binary and executes it. If it can't write into the current directory, it fails to create the link and hence can't execute the program. How was this handled in practice? did users have write permissions on all directories? did you just stay in your directory all the time? . and .. Was this introduced first with PDP-11 unix or did the convention start on the PDP-7 already? It certainly seems to be the case with . but how about ..? the dd directory seems to take on the role of a sort of root directory and the now discovered program pd actually creates a file .. (haven't tried to understand what it does though yet) What does dd stand for, dotdot? directory directory? aap

5 years, 6 months

Re: [TUHS] PDP-7 UNIX file systam

by Doug McIlroy

> As noted in the jargon file, the dd(1) syntax is deliberately reminiscent > of the DD statement in IBM JCL. This was presumably a joke That is certainly true and reflects its major early usage to prepare tapes to carry to other systems. Though I haven't use dit in ages, I recall that the joke was so fully engtained that the command was more likely to be written "dd ifile=x ofile=y" than "dd <x >y" Doug

5 years, 6 months

Re: [TUHS] PDP-7 UNIX filesystem

by jnc＠mercury.lcs.mit.edu

> From: Abhinav Rajagopalan > I only now realized that only mknod existed, up until a long time, only > later on with the GNU coreutils did mkdir as a command come into > existence. Huh? See: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V6/usr/man/man1/mkdir.1 (And probably before that, that was the quickest one to find?) Maybe that was a typo for 'mkdir as a system call'? (I recall having to do a fork() to execute 'mkdir', back when.) But 4.2 had mkdir(). Noel

5 years, 6 months

UNIX: A History and a Memoir by Brian W. Kernighan is now out

by Naveen Nathan

It can be purchased here: https://www.amazon.com/dp/1695978552/ - Naveen

5 years, 6 months

Re: [TUHS] What was your "Aha, Unix!" moment?

by jnc＠mercury.lcs.mit.edu

> From: Sean Dwyer > chdir seems to be a syscall in 7 (sys4.c) It's been a system call forever, see e.g.: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V1/man/man2/chdir.2 (And the working dir was a property of the process, not data in the shell.) Noel

5 years, 6 months

Re: [TUHS] What was your "Aha, Unix!" moment?

by Norman Wilson

Bakul Shah: Being an OS student I had read "The Unix Timesharing System" paper by Ritchie and Thompson and had wanted to use Unix years before I actually had the chance. I don't remember an "Aha!" moment but I took to it like a duck to water. Most everything felt just so comfortable and right. It was very much as I had imagined it to be. ===== That's more or less what it was like to me. Not so much an aha! moment, more just a feeling of coming home. It took a while to understand the different way things worked in UNIX (I had previously used TOPS-10 for several years) but as it all sank in it felt more and more right. C felt the same way. It took me a while to grok the pointer syntax (I had done a lot of MACRO-10 programming so I certainly understood the concept, just not how it fit into the higher- level language), but things like the three-clause condition in for so that all control for a loop could be in one place were just magically right. I don't think I read the CACM paper before I touched UNIX, but I had read both editions of Software Tools, so my brain was perhaps pre-seeded with some of the ideas. Norman Wilson Toronto ON

5 years, 6 months

Re: [TUHS] What was your "Aha, Unix!" moment?

by jnc＠mercury.lcs.mit.edu

> From: Warren Toomey <wkt(a)tuhs.org> > But wasn't "chdir" built into the PDP-7 Unix shell? No. See "The Evolution of the Unix Time-sharing System", in section "Process control". Also, the old 'cd' had different syntax than today's (since there was no notion of a pathname in the earliest Unix); it took instead a list of directories (e.g. "cd dd ken"). Noel

5 years, 6 months

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