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

Noel Chiappa jnc at mercury.lcs.mit.edu
Fri Dec 4 01:21:50 AEST 2015

    > 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:

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:


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.


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