[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Noel Chiappa]

    > From: Will Senn <will.senn at gmail.com>

    > I am studying Unix v6 using SimH and I am documenting the process

I did a very similar exercise using the Ersatz11 simulator; I have a lot
of stuff about the process here:

  http://www.chiappa.net/~jnc/tech/V6Unix.html
  
It contains a number of items that you might find useful, e.g.: "V6 as
distributed is strictly a 20th Century operating system. Literally. You can't
set the date to anytime in the 21st century, for two reasons. First, the
'date' command only take a 2-digit year number. Second, even if you fix that,
the ctime() library routine has a bug in it that makes it stop working in the
closing months of 1999."

    > the PDP architecture

Technically, a PDP-11 - there were a number of different PDP architectures:

  https://en.wikipedia.org/wiki/Programmed_Data_Processor

is a decent listing of them; several (PDP-8, PDP-10, etc) were very popular
and successful.


A few things I noted in your first post:

    > I am using the Ken Wellsch tape because it boots and is stated to be
    > identical to Dennis Ritchie's tape other than being bootable and having
    > a different timestamp on root. 

The only differences I could discover between the two are that in the Wellsch
versions i) a Western Electric rights notice (which prints on booting) has
been added to ken/main.c, and the Unix bootable images; and ii) the RK pack
images do have, as you noted, the bootstrap in block 0.

    > Note: sh is critically important, don't muck it up :). The issue is
    > that if you do, there really isn't an easy way to recover. 

One should _never_ install a new shell version as '/bin/sh' until it has been
run and tested for a while (for the exact reason you mention). Happily, in
Unix, as far as the OS is concerned, the command interpreter is just another
program, so it's trivial to name a new binary of the shell 'nsh' or
something, and run that for a while to make sure it's working OK, before
installing it as '/bin/sh'.

    > a special file (whatever that is)

Special files are UNIXisms for 'devices'. _All_ devices in Unix appear as
'special files' in the file system, usually (but not necessarily) in /dev -
that location is a convention, not a requirment of the OS.

	Noel

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Random832]

On 2015-12-03, Noel Chiappa wrote:
> I did a very similar exercise using the Ersatz11 simulator; I have a lot
> of stuff about the process here:
>
>   http://www.chiappa.net/~jnc/tech/V6Unix.html
>   
> It contains a number of items that you might find useful, e.g.: "V6 as
> distributed is strictly a 20th Century operating system. Literally. You can't
> set the date to anytime in the 21st century, for two reasons. First, the
> 'date' command only take a 2-digit year number. Second, even if you fix that,
> the ctime() library routine has a bug in it that makes it stop working in the
> closing months of 1999."

I don't think your fix to the date command is accurate. The description says:

>  The 'date' command has been extended to support 2- and 4-digit year
>  numbers (to be upwardly compatible, the 2-digit ones assume 19xx).

But the code says:
>	if ((y < 0) || (yh < 0)) {
>		time(nt);
>		y = localtime(nt)[5];
>		y =+ 1900;
>	}
>	  else
>		y = yh + y;

To match your description it should be
	if ((y < 0) && (yh < 0)) {
		time(nt);
		y = localtime(nt)[5];
	} else if(y < 0) {
		/* yh = two digit year */
		y = 1900 + yh;
	} else
		y = yh + y;

Though I'd be inclined to add "if (y < 1970) y =+ 100;" to bring it in line
with modern systems' 1970-2069 range for two-digit years.

Of course, _any_ ancient unix system (and a fair few modern ones) can't
represent dates past 2038. We've only got 23 years left before attempts to
bring up old systems will need some trickery (maybe set the year to 28 or 56
years before the present... that trick, with increasing windows, will work
until 2100 isn't a leap year)

On the other hand, treating it as an "unsigned" value will last about as long
and is a bit less of a hack. But as you note, doing this sort of thing in V6 C
isn't trivial.

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Will Senn]

Noel,

Thank you for writing and responding to my writeup. I have replied 
inline, below:

On 12/3/15 9:21 AM, Noel Chiappa wrote:
>      > From: Will Senn <will.senn at gmail.com>
>
>      > I am studying Unix v6 using SimH and I am documenting the process
>
> I did a very similar exercise using the Ersatz11 simulator; I have a lot
> of stuff about the process here:
>
>    http://www.chiappa.net/~jnc/tech/V6Unix.html
>    
Thanks for reminding me about your work. I had scanned it briefly when I 
was first starting down this road, but wrote it off because I wasn't 
using the Ersatz11 simulator. With the background I have now, it should 
be translate into my current frame and be useful. I haven't tried 
tackling the time problem yet, but I will keep your document in mind 
along with Wolfgang's fixes for ctime:

     http://www.tuhs.org/Archive/PDP-11/Bug_Fixes/V6enb/

>
>      > the PDP architecture
>
> Technically, a PDP-11 ...
Oops. I will be more careful in how I refer to the PDP-11 from now on.
> The only differences I could discover between the two are that in the Wellsch
> versions i) a Western Electric rights notice (which prints on booting) has
> been added to ken/main.c, and the Unix bootable images; and ii) the RK pack
> images do have, as you noted, the bootstrap in block 0.
Thanks for this. I will update my note appropriately.
>      > Note: sh is critically important, don't muck it up :). The issue is
>      > that if you do, there really isn't an easy way to recover.
>
> One should _never_ install a new shell version as '/bin/sh' until it has been
> run and tested for a while (for the exact reason you mention). Happily, in
> Unix, as far as the OS is concerned, the command interpreter is just another
> program, so it's trivial to name a new binary of the shell 'nsh' or
> something, and run that for a while to make sure it's working OK, before
> installing it as '/bin/sh'.
This is a duh moment for me. I will change the note to reflect testing 
first, then copy over.
>
>      > a special file (whatever that is)
>
> Special files are UNIXisms for 'devices'. _All_ devices in Unix appear as
> 'special files' in the file system, usually (but not necessarily) in /dev -
> that location is a convention, not a requirment of the OS.
>
I have since learned a lot more about this and will update the note.

Regards,

Will

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Noel Chiappa]

    > From: Will Senn <will.senn at gmail.com>

    > a deeper read will require the reader to have knowledge beyond what is
    > required of most modern software developers (PDP-11 architecture,
    > assembly language, and UNIX are prerequisite).

Well, for pretty much any _operating system_ (as opposed to applications),
one will need to know something about the details of the machine it is
intended to run on; depending on which part of the OS one is looking at, it
will be more or less. E.g. switching processes probably requires a fair
amount, since one needs to know about internal CPU registers, etc; whereas
working on the file system, one probably doesn't need to know very much about
the machine.

    > It will also require access to a lab where the ideas covered can be
    > experimented with. 

Actually, Lions/V6 was used in operating systems courses using simulated
machines; one at MIT, 6.828 "Operating Systems Engineering":

  https://pdos.csail.mit.edu/6.828/

used it for a while before the students started complaining about being
forced to learn an obsolete machine. They thereupon wrote a V6 clone for the
x86 architecture, 'XV6' (see the top of that page), which is apparently now
used for similar courses at quite a few other universities.

    > The v6 kernel ... packs in features that were either unavailable in
    > larger more established systems or may have been present in some form,
    > but were orders of magnitude more lines of code and attendant
    > complexity. It was and remains an amazing operating system and worthy
    > of contemporary study.

I don't think you will find too many people here who disagree! ;-)

    > So, I was thinking that next up, I would write up notes to help the
    > modern reader engage with v6 more easily in order to follow works like
    > Lyons.

Check around online to see what exists, first; there has been stuff written
since Lions! ;-)

	Noel

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Will Senn]

Noel,

Comments below:

On 12/3/15 9:42 AM, Noel Chiappa wrote:
> Actually, Lions/V6 was used in operating systems courses using simulated
> machines; one at MIT, 6.828 "Operating Systems Engineering":
>
>    https://pdos.csail.mit.edu/6.828/

I knew about xv6, but didn't realize they had used v6 previously. 
Interesting. I can imagine how students might complain about it in a 
college setting. Thankfully, I'm not trying to teach it in one of my 
courses, at least not yet! :). I am just blogging about it for those who 
might be interested.
> Check around online to see what exists, first; there has been stuff written
> since Lions! ;-)
>
In your view, what are some of the best recent works?

Thanks,

Will

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Greg 'groggy' Lehey]

On Thursday,  3 December 2015 at 10:42:00 -0500, Noel Chiappa wrote:

> E.g. switching processes probably requires a fair amount, since one
> needs to know about internal CPU registers, etc;

And there you missed your cue :-) From swtch() in sys/ken/slp.c:

	/*
	 * If the new process paused because it was
	 * swapped out, set the stack level to the last call
	 * to savu(u_ssav).  This means that the return
	 * which is executed immediately after the call to aretu
	 * actually returns from the last routine which did
	 * the savu.
	 *
	 * You are not expected to understand this.
	 */

Greg
--
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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Win Treese]

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> On Dec 3, 2015, at 7:52 PM, Greg 'groggy' Lehey <grog at lemis.com> wrote:
> 	/* […]
> 	 * You are not expected to understand this.
> 	 */

Some of you may have been around for this USENIX
happening (or may even have been involved)!

Dennis was there wearing a "You are not expected to
understand this" T-shirt. A USENIX novice went up to
him and said "Oh, I can tell you about that." He started
going on about what the code is supposed to be doing.

Dennis stood there politely, not saying anything.

Finally, a USENIX old hand decided to rescue him.
"Come on, Dennis, we're heading off to dinner."

The novice looked down at Dennis’s nametag and
turned red.

Dennis said, "That's what we thought at first, but we
were wrong.”

 - Win

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[John Cowan]

Win Treese scripsit:

> Dennis was there wearing a "You are not expected to
> understand this" T-shirt. A USENIX novice went up to
> him and said "Oh, I can tell you about that." He started
> going on about what the code is supposed to be doing.

Which shows that it's not only women who are the objects of mansplaining.

-- 
John Cowan          http://www.ccil.org/~cowan        cowan at ccil.org
The whole of Gaul is quartered into three halves.
        --Julius Caesar

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Will Senn]

All,

I am studying Unix v6 using SimH and I am documenting the process, as I 
go, as part of my own learning process. I have much to learn about Unix, 
Unix v6 in particular, the PDP architecture and its relationship with 
v6, and SimH's emulation of the PDP, so, I am taking notes... I thought 
that I would share the notes in raw form as occasional blog posts in the 
hope that the knowledge that I work to obtain, might be made available 
and useful to others. I also believe that these forms of communication, 
as insignificant as they may seem individually are part of helping to 
preserve the knowledge of our computing history, in the aggregate. Here 
is a link to the first post, a run at an installation walk-through:

http://decuser.blogspot.com/2015/11/installing-and-using-research-unix.html

I am open to feedback and criticism, but please keep in mind that I am a 
relative newbie to v6 and PDP land, some of my assumptions are 
probably/undoubtedly wrong, but definitely fixable :).

Regards,

Will

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Warren Toomey]

On Wed, Dec 02, 2015 at 03:37:42PM -0600, Will Senn wrote:
> I am studying Unix v6 using SimH and I am documenting the process,
> http://decuser.blogspot.com/2015/11/installing-and-using-research-unix.html

That's a great writeup Will. The only comment I have is a pedantic one:
can you write "pdp" as "PDP-11"?

Otherwise, it's highly readable, explain why you did things the whay you
did, and someone else should be able to read your notes and reproduce your
work.

What do you plan to do next?

Cheers, Warren

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Will Senn]

Warren,

Thanks for the comment. I appreciate your feedback and will make 
appropriate changes.

Next? I have been reading Lyons and it has taken me some time to develop 
enough background knowledge to make sense of his notes. A surface read 
of the notes will give a novice reader some idea of the major 
architectural components of the system, but a deeper read will require 
the reader to have knowledge beyond what is required of most modern 
software developers (PDP-11 architecture, assembly language, and UNIX 
are prerequisite). It will also require access to a lab where the ideas 
covered can be experimented with. A modern reader might be intrigued 
from a historical perspective, but may not be compelled to go to the 
trouble of learning enough about the past to recreate it or even see the 
its relevance to the present or future.

Access in 2015 to a working UNIX v6 environment on a PDP-11 ala 1975 is 
as unlikely as it sounds. However, using SimH to simulate a functional 
PDP-11, with peripherals, a UNIX v6 tape image from 1975, and the 
documentation from that period, which, thanks to TUHS is now accessible, 
it becomes possible to establish a laboratory from which to experiment. 
The resulting environment is not only historically interesting, but 
technically interesting, as well.

Many of the interesting bits about our current systems, even seemingly 
unexplainable things like magic numbers, have their genesis and rational 
in this early system. The v6 kernel weighs in at around 10k lines of 
code with a limited set of peripherals and yet it packs in features that 
were either unavailable in larger more established systems or may have 
been present in some form, but were orders of magnitude more lines of 
code and attendant complexity. It was and remains an amazing operating 
system and worthy of contemporary study.

So, I was thinking that next up, I would write up notes to help the 
modern reader engage with v6 more easily in order to follow works like 
Lyons. Right now, I am working on notes related to using the v6 assembly 
and c languages to produce working code. While this may seem trivial to 
folks who are expert, or who have worked in the actual environments, it 
is not really so trivial for me or for other folks brought up on more 
modern computing platforms and I would like to both understand the 
workflows and to document them for others.

Regards,

Will



> On Wed, Dec 02, 2015 at 03:37:42PM -0600, Will Senn wrote:
>> I am studying Unix v6 using SimH and I am documenting the process,
>> http://decuser.blogspot.com/2015/11/installing-and-using-research-unix.html
> That's a great writeup Will. The only comment I have is a pedantic one:
> can you write "pdp" as "PDP-11"?
>
> Otherwise, it's highly readable, explain why you did things the whay you
> did, and someone else should be able to read your notes and reproduce your
> work.
>
> What do you plan to do next?
>
> Cheers, Warren

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Dave Horsfall]

On Wed, 2 Dec 2015, Will Senn wrote:

> Next? I have been reading Lyons [...]

Lions.  The name is Lions.  He was one of my CompSci lecturers.

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Will Senn]

Dave,

Thanks for catching this. I have no idea where I got Lyons from. Sheesh, 
I have his book right here on the table... I will make appropriate edits.

Regards,

Will


On 12/2/15 10:11 PM, Dave Horsfall wrote:
> On Wed, 2 Dec 2015, Will Senn wrote:
>
>> Next? I have been reading Lyons [...]
> Lions.  The name is Lions.  He was one of my CompSci lecturers.
>

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Peter Jeremy]

On 2015-Dec-02 22:18:11 -0600, Will Senn <will.senn at gmail.com> wrote:
>Thanks for catching this. I have no idea where I got Lyons from.

Well, at least one "Lyons" has a proud place in computer history - have
a read of https://en.wikipedia.org/wiki/LEO_(computer)

-- 
Peter Jeremy
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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[John Cowan]

Peter Jeremy scripsit:

> Well, at least one "Lyons" has a proud place in computer history - have
> a read of https://en.wikipedia.org/wiki/LEO_(computer)

Joseph Nathaniel Lyons himself had nothing to do with the computer, of course.
But then again, Emack and Bolio had nothng to do with the ice-cream store,
either.

-- 
John Cowan          http://www.ccil.org/~cowan        cowan at ccil.org
Time alone is real
  the rest imaginary
like a quaternion       --phma

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Dave Horsfall]

On Thu, 3 Dec 2015, Peter Jeremy wrote:

> >Thanks for catching this. I have no idea where I got Lyons from.
> 
> Well, at least one "Lyons" has a proud place in computer history - have 
> a read of https://en.wikipedia.org/wiki/LEO_(computer)

Wow!  Mercury tanks...  I have a fascination for olde computers.

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Greg 'groggy' Lehey]

On Friday,  4 December 2015 at 17:22:09 +1100, Dave Horsfall wrote:
> On Thu, 3 Dec 2015, Peter Jeremy wrote:
>
>>> Thanks for catching this. I have no idea where I got Lyons from.
>>
>> Well, at least one "Lyons" has a proud place in computer history - have
>> a read of https://en.wikipedia.org/wiki/LEO_(computer)
>
> Wow!  Mercury tanks...  I have a fascination for olde computers.

Take a look at CSIRAC in the Melbourne museum, the oldest computer in
the world.  It's worth it, even if they don't have it running.

Greg
--
Sent from my desktop computer.
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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[John Cowan]

Greg 'groggy' Lehey scripsit:

> Take a look at CSIRAC in the Melbourne museum, the oldest computer in
> the world.  It's worth it, even if they don't have it running.

Well, there's the Antikythera mechanism.

-- 
John Cowan          http://www.ccil.org/~cowan        cowan at ccil.org
In the sciences, we are now uniquely privileged to sit side by side
with the giants on whose shoulders we stand.  --Gerald Holton

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Ronald Natalie]

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I guess you’re going to have to qualify that.   It’s the oldest “surviving” (though it’s unclear what that means to a computer not running) STORED PROGRAM machine.

The ENIAC, which by some standards is the first programmable digital computer still exists at the Smithsonian.  Some of my coworkers there were on the team that took it down from BRL to the Smithsonian and actually tested it as operational when it was handed over to the museum.   I don’t think it’s ever been powered on since.

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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Gregg Levine]

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Hello!
We are also forgetting the contraption that Turing built. Of course
sadly at the end it was destroyed. Why? I don't know. But it has since
been rebuilt.
-----
Gregg C Levine gregg.drwho8 at gmail.com
"This signature fought the Time Wars, time and again."


On Fri, Dec 4, 2015 at 1:17 PM, Ronald Natalie <ron at ronnatalie.com> wrote:
> I guess you’re going to have to qualify that.   It’s the oldest “surviving” (though it’s unclear what that means to a computer not running) STORED PROGRAM machine.
>
> The ENIAC, which by some standards is the first programmable digital computer still exists at the Smithsonian.  Some of my coworkers there were on the team that took it down from BRL to the Smithsonian and actually tested it as operational when it was handed over to the museum.   I don’t think it’s ever been powered on since.
>
>
> _______________________________________________
> TUHS mailing list
> TUHS at minnie.tuhs.org
> https://minnie.tuhs.org/mailman/listinfo/tuhs
>

[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Greg 'groggy' Lehey]

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On Friday,  4 December 2015 at 13:17:58 -0500, Ronald Natalie wrote:
>
> I guess you???re going to have to qualify that.  It???s the oldest
> ???surviving??? (though it???s unclear what that means to a computer
> not running) STORED PROGRAM machine.

Guilty as charged.

> The ENIAC, which by some standards is the first programmable digital
> computer still exists at the Smithsonian.  Some of my coworkers there
> were on the team that took it down from BRL to the Smithsonian and
> actually tested it as operational when it was handed over to the
> museum.  I don???t think it???s ever been powered on since.

My understanding, which is borne out by the Wikipedia article, is that
only parts of ENIAC are on display at the Smithsonian.  It lists a
number of other places with parts.

But then there's yet another computer, the Zuse Z4 at the Deutsches
Museum in München.  Again from Wikipedia, it was built between 1942
and 1945, and thus predates ENIAC.  It seems that it's complete, but
of course it's not electronic.  So until proof of the contrary, CSIRAC
is the oldest surviving complete electronic computer.

Do I need more adjectives?

Greg
--
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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[SZIGETI Szabolcs]

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Hi,

Don't forget the Zuse machines, which were later proven to be Turing
complete. It is certainly fascinating to see handling binary floating point
numbers in a purely mechanical device (check it out if you happen to be in
Berlin). Later machines were electromechanical and electronics.

Regards,
Szabolcs

>
> 2015.12.04. 15:52 ezt írta ("John Cowan" <cowan at mercury.ccil.org>):
>>
>> Greg 'groggy' Lehey scripsit:
>>
>> > Take a look at CSIRAC in the Melbourne museum, the oldest computer in
>> > the world.  It's worth it, even if they don't have it running.
>>
>> Well, there's the Antikythera mechanism.
>>
>> --
>> John Cowan          http://www.ccil.org/~cowan        cowan at ccil.org
>> In the sciences, we are now uniquely privileged to sit side by side
>> with the giants on whose shoulders we stand.  --Gerald Holton
>> _______________________________________________
>> TUHS mailing list
>> TUHS at minnie.tuhs.org
>> https://minnie.tuhs.org/mailman/listinfo/tuhs
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[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

[Peter Jeremy]

On 2015-Dec-04 17:22:09 +1100, Dave Horsfall <dave at horsfall.org> wrote:
>On Thu, 3 Dec 2015, Peter Jeremy wrote:
>
>> >Thanks for catching this. I have no idea where I got Lyons from.
>> 
>> Well, at least one "Lyons" has a proud place in computer history - have 
>> a read of https://en.wikipedia.org/wiki/LEO_(computer)
>
>Wow!  Mercury tanks...  I have a fascination for olde computers.

Well, whilst I've replaced the 'U' in this mailing list with a 'C'...
LEO-1 was basically a commercialised EDSAC.  And there's an EDSAC
Replica Project - http://www.tnmoc.org/special-projects/edsac  I
saw a fascinating talk by one of the Project members.

-- 
Peter Jeremy
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