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

Will Senn will.senn at gmail.com
Thu Dec 3 12:37:14 AEST 2015


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.



> 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

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