Otto Moerbeek wrote:
On Mon, 12 Jun 2006, Ted Mittelstaedt wrote:
-----Original Message-----
From: John Nemeth [mailto:[EMAIL PROTECTED]
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;
[EMAIL PROTECTED]
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. ;-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [EMAIL PROTECTED] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
