I just saw in another thread the statement their are no odd requests here.
So I thought I would test that.
The day NeXT took over Apple I read a page somewhere on the internet that started with line.
Bow down to UNIX children of Macintosh... It then when on its Old Testament conquering tone about the new way of computing that was coming.
Does anybody have any idea who wrote this or where to find it?
I am Rocky and this is my first message. Before starting, I would like to thank you for all the valuable informations and stories you post here.
About the History of Unix, I was wondering with another guy why the rc script has that name. As many of you already know, and according to NetBSD, FreeBSD, OpenBSD (current) manual,
"The rc utility is the command script which controls" the startup of various services, "and is invoked by init(8)" (from DESCRIPTION).
"The rc command appeared in 4.0BSD" (from HISTORY).
Words may slightly change between the three distributions, but the meaning and the informations provided are the same. So, the etymology of rc does not appear in the man pages. Do you know how to recover it? Do (or did) the letters rc have some meaning in this context?
On 2016-03-25 00:27, Milo Velimirovic wrote:
>> On Mar 24, 2016, at 6:06 PM, Johnny Billquist <bqt(a)update.uu.se> wrote:
>> On 2016-03-24 23:50, Peter Jeremy wrote:
>>> On 2016-Mar-24 11:17:18 +0100, Johnny Billquist <bqt(a)update.uu.se> wrote:
>>>> It is the normal behavior of any instruction that interrupts are not
>>>> recognized until the next instruction fetch. This is how the microcode
>>>> works, and it is also pretty much the same in any processor today.
>>>> individual instructions. You still get a fetch between each instruction,
>>>> at which point, interrupts will be recognized.
>>> Some instructions inhibit the "check for interrupts at the end of this
>>> instruction" check. I'm most familiar with the 8080 EI instruction,
>>> which enabled interrupts after the following instruction (so things like
>>> EI;HLT didn't have a window). It seems the PDP-11 SPL behaves the same.
>> I don't think it should on the PDP-11, and the documentation do not mention any such thing.
>> There is a good reason the 8080 (and Z80, and others) have this property. The RETI instruction on these machines do not enable itnerrupts themselves, so just as you note, you need to both enable interrupts and return from interrupt atomically, or else you get into a mess.
>> The PDP-11 RETI instruction changes the processor priority as a part of the instruction. You do not use SPL (whatever) before a RETI.
>> Thus, it do not make sense that SPL on a PDP-11 would have this property. If if indeed do disable recognizing interrupts after an SPL, it sounds more like a bug. I guess I'll go and read the microcode so see if that mentions any of this, since I'm sortof into reading it anyway as I was trying to debug a problem on an 11/70 only a couple of months ago…
> The PDP-11 has no RETI instruction; it has a RTT (ReTurn from Trap) and a RTI (ReTurn from Interrupt) instructions, but you already knew that, right? In some cases it’s problem that it’s not possible to determine which is appropriate or correct to use. According to the PDP11 Architecture Handbook the difference between them is in what happens when the RTx instruction loads a PSW that has the T bit set and when it forces a Trace trap. RTI - immediate trap, RTT traps after the instruction following the RTT.
Oops. Yes, it's RTI and RTT. But the names are beside the point, and so
is the difference between these two. The point is that the
instruction(s) do set the processor priority level, and you do not use
SPL in combination with them, so it makes no sense to have SPL inhibit
interrupts for any length at all. (And yes, I did know that.)
Oh, and as far as RTT vs. RTI goes, not it's not hard to know which one
you want. You want RTT for your debugger and RTI for everything else.
The difference is about what happens after the return. With RTT, the
T-bit trap will not trap until another instruction has executed. With
RTI, you would never manage to step to the next instruction with the
T-bit, since every time you returned, you'd get another trap.
But I bet you knew that as well... ;-)
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
Seems like we are all contributing old card stories.. here is one of my
favorites from my past.
At CMU, all systems programmers working for the computer center had to put
shifts in as the operator behind the "glass door" doing the grunt stuff
(but we got all the computer time we wanted, an office and terminal - so it
was a good deal in those days). The student courses, in particular the
engineering intro to FORTRAN (WATFIV), used the TSS based 360/67 which we
programmed and ran; but they used the batch system on cards not timesharing
with the ASR 33's which was quite expensive. There was a traditional glass
room with the computer, its tapes and other gear, and a counter with a
"call human for help" button where "paying users'" could come ask questions
of the operator on duty. On the older side of the counter was the flock
of keypunch machines and a high speed card read. The printers were in
secure areas, so we would bring out student prints from their batch jobs as
needed and put them on the binds near the counter ( as was the pretty much
the standard of those days).
By rule, the system's programmers were also not supposed to help the
students with their assignments. They were supposed to get help from their
TA's and Profs, *etc*. who had regular hours. But often folks were up
very late working on assignments and no one from the course was around to
ask questions. And as the operator, if you had a minute, it was not
uncommon to have a little empathy for your brothers and sisters in arms on
the other side of the counter. As long as this was not abused, the TA's,
Profs as well as our bosses in the computer center tolerated the process.
But if we were obviously busy, we really did not have the time to do much
to help them.
One night I was working the over night operator shift with another coworker
who will be left nameless (but I will say that he's now a SVP at a large
computer firm these days). It was a very busy night for us for some
reason, probably something like printing bills, or checks for the school or
some such; along with a full backup, so we had our hands full between
mounting tapes, changing types of paper and print heads *etc.*, security
procedures with the results and the like. That night, there was also a big
assignment due shortly for one of the classes.
Sure enough the buzzer started ringing and it was a frustrated (and as I
remember somewhat clueless) student that needed help with his assignment.
He was claiming that the his deck was being rejected/was not working.
Note "turn around" from deposit card deck to receipt of print out was
probably in the order of 10-15 minutes, and sometimes longer. One of us
came out, showed him something like a missing "BATCH WATFIV" command card
or some such and reminded them of the official policy and probably pointed
to the sign, as we were very busy with our job. We would politely tell
them to try to find a TA or someone in the class that could help him.
The student went away, and we went back to work. A few minutes later the
buzzer went off again, same student, and the cycle repeated with some other
trivial issue. After the 4th or 5th time it was becoming a real issue
because we were really quite busy. At that point, my coworker came out and
said, here bring me your deck. He looked at them and quickly said -- "The
problem is you used the wrong color cards."😈
The student was completely dejected and walked away. I looked up and
said, man that was cruel. But it did buy us time to finish our work.
Never found out if he re-keypunched his cards.
This reminds me that someone at BTL threw together a "TSO Shell". It was
a wrapper around /bin/sh that slept for 10 seconds before executing each
And after each command exited. Discarding anything typed ahead
during the sleep, of course.
And printed all-upper-case IEFCRAPNONSENSE messages even when a
command exited successfully.
I think I still have a copy somewhere. It dates from the 6/e era,
so it would need a lot of work to compile and run on a modern system.
Occasionally I think of converting it to ISO and POSIX even though
that seems contradictory somehow.
Not quite a self reproducing program and I did take down one of the UCSD servers one day.
I was writing a shell script to do some complex and long running task. This was in the early days of the shell supporting functions. The script had a large number of functions and I named one of them to be the same name as the shell script.
I set it in motion and logged out, as I knew it would take several hours to finish the work.
The next day I logged in to find that the machine had the load spike as the shell script recursively started itself when it got to the function call that had the same name as the shell script. The admin kindly sent me a ‘top' output showing the load at several hundred and all the jobs having my name and being my shell script.
Under this he wrote: “Never do this again.”
> Btw. It does not emulate the smell of small machine oil
or the mess of ppt punch chaff on the floor
Yes. I saw Clem's mail just as I was about to recommend
placing a small dish of machine oil beside the simulator.
Alas, it seems I missed out on the chad experience. Data was
regularly imported to the PDP-7 by ppt, but rarely exported.
Night-owl Ken must have taken some ppt backups, evidence of
which the midnight janitors whisked away.
It's a bit off-topic, but what were non-Unix filesystems like around 1969-1970?
The PDP-7 filesystem has i-nodes (file metadata) and filenames separate
from the i-nodes. This allows hard links and thus a non-tree structured
This has always struck me to be one of the most important features of
the Unix filesystem: names separated from the rest of the file metadata,
and arbitrary hard links so that there is no preferred filename.
Were these features in other contemporaneous filesystems?
As a side note, the PDP-7 kernel knows about the top-level directory ("dd")
but it is agnostic to the concept of "." and "..". What that means is
that you can build a filesystem with "." and ".." links and the kernel
will deal with them as per all other links. But you can also build a
filesystem without "." or ".." and the kernel doesn't care.
There's not enough evidence (source code, papers, anecdotes) to confirm
or deny the presence of "." in the PDP-7 code that Norman scanned for us.
".." does seem to exist as it is mentioned in one source file, ds.s.
It's an intruiging mystery.