From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Wed,  9 Dec 2015 08:30:27 -0500 (EST)
Subject: [TUHS] v6tar from v7 on v6, too large?
Message-ID: <20151209133027.DCD0D18C0C7@mercury.lcs.mit.edu>

    > From: Ronald Natalie

    > I'm pretty sure the V6 kernel didn't run in split I/D.

Nope. From 'SETTING UP UNIX - Sixth Edition':

  "Another difference is that in 11/45 and 11/70 systems the instruction and
  data spaces are separated inside UNIX itself."

And if you don't believe that, check out:

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/conf/m45.s

the source! ;-)


    > It wasn't too involved of a change to make a split I/D kernel.
    > Mike Muuss and his crew at JHU did it.

Maybe you're remembering the process on a pre-V6 system?

    > We spent more time getting the bootstrap to work than anything else I
    > recall.

It's possible you're remembering that, as distributed, V6 didn't support load
images where the text+initialized-data was larger than 24KW-delta; it would
have been pretty eaay to up that to 28KW-delta (change a parameter in the
bootstrap source, and re-assemble), but after that, the V6 bootstrap would
have had to have been extensively re-worked.

And there were _also_ a variety of issues with handling maximal large images
in the startup code. Once operating, the kernel has segments KI1-KI7 available
the hold the system's code; however, it's not clear that all of KI1-7 are
really usable, since the system can't 'see' enough code while in the code
relocation phase in the startup to fill them all. E.g. during code relocation,
KI7 is ripped off to hold a pointer to I/O space (since KD7 is set to point to
low memory just after the memory that KD6 points to).

These might have been issues in systems which were ARPANET-connected (i.e.
ran NCP), as that added a very large amount of code to the kernel.

	Noel