From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Tue,  6 Jan 2015 21:18:42 -0500 (EST)
Subject: [TUHS] pdp11 UNIX memory allocation.
Message-ID: <20150107021842.2642418C09B@mercury.lcs.mit.edu>

    > From: Ronald Natalie <ron at ronnatalie.com>

    > Yep, the only time this was ever trully useful was so you could put an
    > a.out directly into the boot block I think.

Well, sort of. If you had non position-independent code, it would blow out
(it would be off by 020). Also, some bootstraps (e.g. the RL, IIRC) were so
close to 512. bytes long that the extra 020 was a problem. And it was so easy
to strip off:

   dd if=a.out of=fooboot bs=1 skip=16

I'm not sure that anything actually used the fact that 407 was 'br .+020', by
the V6 era; I think it was just left over from older Unixes (where it was not
in fact stripped on loading). Not just on executables running under Unix; the
boot-loader also stripped it, so it wasn't even necessary to strip the a.out
header off /unix.

	Noel