Date: Tue, 13 Jun 2006 12:02:11 +0200 From: Johnny Billquist <bqt@update.uu.se> To: Otto Moerbeek <otto@drijf.net> Cc: John Nemeth <jnemeth@victoria.tc.ca>, misc@openbsd.org, Ted Unangst <ted.unangst@gmail.com>, Ted Mittelstaedt <tedm@toybox.placo.com>, freebsd-questions@freebsd.org, =?ISO-8859-1?Q?H=E1morszky_Bal=E1zs?= <balihb@ogyi.hu>, netbsd-users@NetBSD.org, Nikolas Britton <nikolas.britton@gmail.com> Subject: Re: wikipedia article Message-ID: <448E8D23.5030008@update.uu.se> In-Reply-To: <Pine.BSO.4.64.0606130802280.16242@lou.intra.drijf.net> References: <LOBBIFDAGNMAMLGJJCKNMEBMFEAA.tedm@toybox.placo.com> <Pine.BSO.4.64.0606130802280.16242@lou.intra.drijf.net>
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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. ;-)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt@update.uu.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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