On Tue, 13 Jun 2006, Johnny Billquist wrote:

> Otto Moerbeek wrote:
> > On Mon, 12 Jun 2006, Ted Mittelstaedt wrote:
> > 
> > 
> > > > -----Original Message-----
> > > > From: John Nemeth [mailto:jnemeth@victoria.tc.ca]
> > > > Sent: Monday, June 12, 2006 1:15 PM
> > > > To: Ted Mittelstaedt; Nikolas Britton; Ted Unangst
> > > > Cc: Hamorszky Balazs; misc@openbsd.org; freebsd-questions@freebsd.org;
> > > > netbsd-users@NetBSD.org
> > > > Subject: RE: wikipedia article
> > > > 
> > > > 
> > > > On Nov 1,  6:11pm, "Ted Mittelstaedt" wrote:
> > > > }
> > > > } Prior to the release of the 80386 the Intel processors didn't have
> > > > } memory protection which was a requirement of any processor running
> > > > } the BSD kernel.
> > > > 
> > > >    This is not entirely true.  The 80286 had memory protection.
> > > > However, its memory protection was completely based on segments (i.e.
> > > > it could not do paging).
> > > 
> > > Oh, yeah, your right about that.  Me bad.
> > > 
> > > 
> > > > Also, it was only a 16 bit processor.
> > > 
> > > What was the bit size of the CPU's originally used to write UNIX in Bell
> > > Labs?
> 
> The PDP-7 was/is an 18-bit machine.
> 
> > What's more, iirc the MMU of the pdp11 isn't what we call a MMU today,
> > it could not even do paging.
> 
> You're wrong. You could easily do paging on a PDP-11, if you wanted to. The
> main reasons this wasn't done are two.
> 1) Each page is 8K. At the time, that was considered way too large pages for a
> demand page system.
> 2) The address space is only 64 per process, which means you only have 8
> pages. Not only is that perhaps a little little for meaningful paging (most
> programs tend to refer to all 8 pages most of the time). The main memory on a
> PDP-11 is furthermore 4 meg, so having a lot of processes full memory space in
> physical memory at the same time is not a problem.
> 
> The PDP-11 MMU is a beatiful MMU. Nothing like the crap Intel spits out. ;-)

I stand corrected. I always thought it coulnd't do paging, but I
suppose it should be "due to various restrictions, it couldn't do
meaningful paging".

	-Otto