From mboxrd@z Thu Jan  1 00:00:00 1970
From: wkt@minnie.tuhs.org (Warren Toomey)
Date: Mon, 8 Jul 2002 13:43:51 +1000 (EST)
Subject: [TUHS] Other operating systems on the PDP-11
In-Reply-To: <20020708025934.GH90012@wantadilla.lemis.com> from "Greg 'groggy'
 Lehey" at "Jul 8, 2002 12:29:34 pm"
Message-ID: <200207080343.g683hqX97846@minnie.tuhs.org>

In article by Greg 'groggy' Lehey:
> Has anyone successfully gotten, say, NetBSD, or anything along the lines of the
> > 4.4 series to run on a PDP-11?
> 
> The big issue is address space.  It's difficult enough shoehorning
> 2.11BSD onto the PDP-11.  It's well-nigh impossible to retrofit 32 bit
> operating systems.  But Steven M. Schulz will doubtless give you a
> better explanation.
> Greg

More specifically, the issue is data space. Using overlays, you can
have a process with more than 64Kbytes of instruction space on a PDP-11,
but the maximum data space that a process can have is 64Kbytes.

The kernel is in a similar situation, but with some PDP-11 models
there is kernel mode and supervisor mode, giving you two separate
64Kbytes instruction + 64Kbytes data address spaces (and overlays
to increase the I space).

I can't see Linux fitting into 128K of data space, and GCC is definitely
out of the question. Besides, 2.11BSD already looks pretty close to 4BSD :-)

	Warren