TUHS December 2015

tuhs@tuhs.org

53 participants
90 discussions

Re: [TUHS] Does anybody recall how the TU10 bootstrap code actually operates?

by jnc＠mercury.lcs.mit.edu

> Thank you for responding so carefully. The devil is in the details... > I have been reading the PDP-11/40 handbook, much too much :) I'm not sure that's possible! :-) Yes, yes, I know, the architecture is deader than a doornail for serious use, but I liken it to sailing vessels: nobody uses them for serious cargo haul any more, but they are still much beloved (and for good reasons, IMO). The PDP-11 is an incredibly elegant architecture, perhaps the best ever (IMO), which remains one of the very best examples ever of how to get 30 pounds into the proverbial ten-pount sack - like early UNIX (more below). > this is really elegant code. The guys who thought this up were amazing. Nah, it's just a clever hack (small-scale). What is really, almost un-approachably, brilliant about early UNIX is the amount of functionality they got into such a small machine. It's hard to really appreciate, now, the impact UNIX had when it first appeared on the scene: just as it's impossible for people who didn't themselves actually experience the pre-Internet world to _really_ appreciate what it was like (even turning off all one's computers for a day only approximates it). I think only people who lived with prior 'small computer OS's' could really grasp what a giant leap it was, compared to what came before. I remember first being shown it in circa 1975 or so, and just being utterly blown away: the ability to trivially add arbitrary commands, I/O redirection, invisibly mountable sections of the directory tree - the list just goes on and on. Heck, it was better than all but a few 'big machine' OS's! > Thanks again for your help. Eh, de nada. Noel

8 years, 12 months

Re: [TUHS] etymology of cron

by Norman Wilson

John Cowan: Well, of course there are conferences and there are conferences. The only conference I've ever had a paper published at, Balisage, is as peer-reviewed as any journal. (And it is gold open access and doesn't charge for pages -- the storage costs are absorbed as conference overhead.) ==== Have you actually looked up the cited reference? The trouble is not that it's a conference paper. The trouble is that that the `authority' being cited is just a random assertion, not backed up. It's as if I mentioned your name in a paper about something else, remarked in passing and without any citation of my own that you have a wooden leg, and Wikipedia accepted that as proof of your prosthesis. Norman Wilson Toronto ON (Four limbs and eight eyes, thank you very much)

8 years, 12 months

Re: [TUHS] etymology of cron

by jnc＠mercury.lcs.mit.edu

On Dec 22, 2015, at 5:44 PM, Norman Wilson <norman(a)oclsc.org> wrote: > If that's the quality of reference they accept, there is simply no > reason to take anything they publish as gospel. You're mistaking Wikipedia for an information source you can rely on. It's not. It's more akin to an attempt to prove that an infinite number of monkeys, with an infinite number of typewriters, and an infinite amount of time, can produce a reliable encyclopaedia. (Yes, yes, spare me the surveys that show that Wikipedia's error rates aren't that bad, when compared with other encyclopaedias, etc.) Don't get me wrong, Wikipedia is quite useful as a place for an _introduction_ to any topic, but anyone who really wants to _reliably_ know anything about a topic needs to look at the references, not the articles. There was an attempt to do a Wikipedia-like online encyclopaedia that one could rely on - Citizendium - but alas it doesn't seem to have taken off (or hadn't when I got distracted from working on it). And I know whereof I speak; those who wish to be amused may want to read: http://en.wikipedia.org/wiki/User:Jnc/Astronomer_vs_Amateur And apologies for continuing the off-topic (this group certainly can't fix Wikipedia, people have been complaining about this problem for many years now), but some buttons, you just have to respond when they are pushed... Noel

8 years, 12 months

Re: [TUHS] etymology of cron

by Johnny Billquist

On 2015-12-23 17:04, norman(a)oclsc.org (Norman Wilson) wrote: > John Cowan: > > Wikipedia is by nature a*summary of the published literature*. If you > want to get some folklore, like what "cron" stands for, into Wikipedia, > then publish a folklore article in a journal, book, or similar reputable > publication. Random uncontrolled mailing lists simply do not count. > > ====== > > That sounds fair enough on the surface. > > But if you follow the references cited to support the cron > acronyms, you find that random unsupported assertions in > conference papers do count. That's not a lot better. I've had similar experiences with Wikipedia in the past. At one point I was trying to get the PDP-11 article corrected, as it said that the PDP-11 was an architecture that disappeared in the 80s (paraphrasing). I pointed out that the last *new* PDP-11 model from DEC itself was released in 1990, and that others are still making new PDP-11 CPUs. My corrections were reverted, and I was asked for citations. I went through a silly loop of requests for sources for my claims, while there seems to have been no demand for citation for the original claims, more than the "knowledge" of someone. It wasn't until I dug up the system manuals and documentation from DEC about the PDP-11/93 and PDP-11/94 (which have actual time of original publishing date printed) that my claims were (somewhat) accepted. I've also had numerous fights about the Wikipedia articles about virtual memory, where the original authors on the article clearly had not understood the difference between virtual memory and demand paged memory. The articles are better today, but when I last looked, they still had some details wrong in there. And getting anything corrected is hell, as any silly statement that is already in is almost regarded as gospel, and anything you try to correct is questioned to hell and back before anyone will accept it. (Hey, according to Wikipedia, a PDP-11 do not have virtual memory... I wonder what it has then. Fake memory? Although, the article might now actually accept that a PDP-11 do have virtual memory, although no OS I know of implements demand paging, but that could be done as well, if anyone wanted to.) Nowadays, I use Wikipedia to find information, but just take everything in there with a large grain of salt when it comes to details. There are just too many ignorant people who are writing stuff, and who seem to get anything accepted, and too much hassle to get anything corrected when you actually knows the subject. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt(a)softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

8 years, 12 months

Re: [TUHS] etymology of cron

by norman＠oclsc.org

Perhaps Wikipedia would be satisfied if we could get Ken to write a letter to some current published journal, saying that he's the one who named cron, he's heard people are interested in how it got that name, here's how. We could then cite that as a reference. On the other hand, this may be an example of the degree to which one should trust Wikipedia. The `command run on notice' acronym claim is backed up by an article from the AUUG (Hi Warren!) Proceedings, 1994, in which the first reference to cron gives that explanation with no further reference. If that's the quality of reference they accept, there is simply no reason to take anything they publish as gospel. Sorry. Norman Wilson Toronto ON Proud that no one has yet made a spurious Wikipedia page asserting the etymology of my personal domain name.

8 years, 12 months

Re: [TUHS] etymology of cron

by norman＠oclsc.org

Larry McVoy: As a guy who has donated money to Wikipedia this whole thread makes me not want to donate again. Just me being grumpy. ==== Me too. Perhaps we should start our own online encyclopedia. In the Ken tradition we could call it pedi. (pdia sounds better, but pdia.org is already taken.) Norman Wilson Toronto ON

8 years, 12 months

etymology of cron

by Doug McIlroy

I had never doubted that "cron" was a contraction of "chrono-". Wikipedia, however, offered several folk acronyms on a par with it. Brian asked Ken, who confirmed, "cron comes from the prefix (greek?) for time. it should have been chron, but i never could spell." I edited Wikipedia to expunge the nonsense. Amusingly that makes the article less "verifiable" because there had been literature citations for the nonsense, but there is none for the fact. Doug

8 years, 12 months

Does anybody recall how the TU10 bootstrap code actually operates?

by Will Senn

All, I am in the process of gaining a deeper understanding of PDP-11 machine instructions and how the bootstrap loader and its cousins function. As part of that process, I am analyzing the code. I am concurrently working through the DEC bootstrap loader and the bootstrap loader that is described in the v6 documentation. The DEC bootstrap loader, while fascinating and elegant, is relatively straightforward, given its enormous range and the fact that it is self-modifying. I wrote up my preliminary notes here: http://decuser.blogspot.com/2015/12/analysis-of-pdp-11-bootloader-code.html The code that is in the v6 documentation on the other hand is not yielding easily to reasonable interpretation and I was hoping y'all might be able to shed some light on how it works. The following is the TU10 (TM11) bootstrap code from "Setting Up Unix - Sixth Edition": TU10 012700 172526 010040 012740 060003 000777 The author's notes around the code are: The tape should move and the CPU loop. (The TU10 code is not the DEC bulk ROM for tape; it reads block 0, not block 1.) Halt and restart the CPU at 0. The tape should rewind. The console should type ‘=’. Of course, following the instructions results in a successful outcome, but understanding what is happening is difficult given that this is a virtual environment and no discernible tape movement can be detected. My attempt at interpretation is along the following lines, I manufactured the dissasembly based on my reading of the PDP-11/40 handbook and the machine codes: 012700 MOV #172526, R0 ; moves the TM11 Current Memory Address Register (MTCMA) address into R0 172526 ; the immediate operand 010040 MOV R0,-(R0) ; moves the contents of R0, 172526, into memory location 172524, the TM11 Byte Record Counter (MTBRC) 012740 MOV #60003,-(R0); moves 60003 into memory location 172522, the TM11 Command Register (MTC) 060003 ; immediate data 000777 HALT This seems like gobbledegook to me. It moves the MTCMA (Magtape Current Memory Address) into R0, then it moves the MTCMA into the MTBRC (Magtape Byte Record Count), then it moves 60003 into the MTC (Magtape control register), which causes a read operation with 800BPI 9 Channel density. 172526 is -5252 in 2's complement. Am I misinterpreting the byte codes or is this some idiosyncratic way to get the Magnetic tape to rewind or something (the TM11 has a control function to rewind, so it seems unlikely that this is the case, but I'm mystified)? I single stepped through the code in the simulator, and the TM11 registers appear to be pretty unobservable (examining these three registers always displays 0's, but if I change from referencing the TM11 registers to another area of memory, say 100500 I see the values I would expect to see as they are being moved from the registers into memory). Thanks, Will

8 years, 12 months

2.11BSD mirror

by Warren Toomey

Hi all, I've been in contact with Steven Schultz and I've set up a mirror of his 2.11BSD patches at: http://www.tuhs.org/Archive/PDP-11/Distributions/ucb/2.11BSD/Patches/ I have no "git fu", but it would be nice to have a Git repository with all the sources fully patched. Oh, and new boot tapes :-) I should ask Santa for it. Cheers, Warren

8 years, 12 months

ed.c on Unix v5

by Mark Longridge

Ok, not sure if anyone will want to do this but I've just compiled ed.c from Unix v6 on Unix v5. It's not much bigger than the assembled ed, with 1314 lines of C code the compiled executable is only 6518 bytes vs 4292 for the original. I was looking at the source code and didn't see anything that the v5 cc couldn't handle. I trimmed the source a bit, there's a function at the end called getpid() which is commented out. The comment says: /* Get process ID routine if system call is unavailable. */ but my version of v5 does have that system call so it's all good. It's been run a few times and it seems to work just fine. It may even have a few more features than the v5 ed, I'm not sure yet :) Mark

9 years

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TUHS December 2015