From: bqt@update.uu.se (Johnny Billquist)
Subject: [TUHS] /dev/drum
Date: Sat, 28 Apr 2018 12:41:37 +0200 [thread overview]
Message-ID: <cf10aedf-07a0-4475-e7f5-32f40b4faf9f@update.uu.se> (raw)
In-Reply-To: <20180428001920.30BA018C08D@mercury.lcs.mit.edu>
On 2018-04-28 02:19, Noel Chiappa wrote:
> > From: Johnny Billquist
>
> > For 1972 I only found the 11/40 handbook.
>
> I have a spare copy of the '72 /45 handbook; send me your address, and I'll
> send it along. (Every PDP-11 fan should have a copy of every edition of every
> model's handbooks... :-)
Gah. If I were to try and collect every copy made, it would be quite a
collection. Thanks for the offer. If you really want to get rid of one,
and is willing to send to Switzerland, then I'll take it in a private
mail. But you don't really have to.
> In the meantime, I'm too lazy to scan the whole thing, but here's the first
> page of Chapter 6 from the '72:
>
> http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/tmp/PDP11145ProcHbook72pg6-1.jpg
Cool. Thanks. That is a very different terminology. The MMU is not even
called the MMU, but the "Memory Segmentation Unit".
Very interesting.
> > went though the 1972 Maintenance Reference Manual for the 11/45. That
> > one also says "page". :-)
>
> There are a few remnant relics of the 'segment' phase, e.g. here:
>
> http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/conf/m45.s
>
> which has this comment:
>
> / turn on segmentation
>
> Also, if you look at the end, you'll see SSR0, SSR1 etc (as per the '72
> handbook), instead of the later SR0, SR1, etc.
So there was a total change in terminology early in the 11/45 life, it
would appear. I wonder why.
I can only speculate, but I probably would not blame some market droids.
Trying to think about this, I feel that one of the most important
differences between segmentation and pages are that with segmentation
you only have one contiguous range of memory, described by a base and a
length register. This will be a contiguous range of memory both in
virtual memory, and in physical memory. With segmentation you cannot
have your virtual memory split up and spread out over physical memory.
You can also, pretty much, arbitrarily point where in physical memory
your virtual memory starts and ends.
With pages, this is obviously not the case anymore. The PDP-11 do have
the ability to have pages start at close to arbitrary addresses in
physical memory, but you can certainly have your virtual memory spread
out over different places in physical memory. Your virtual memory is
also not just described by a base and length, as you have 8 pages,
starting at fixed virtual memory addresses. You can also have "holes" in
your memory, with pages that are invalid, yet have pages higher up in
your virtual memory which are valid. Something that is impossible with
segmentation, since you only have one set of registers for each memory
type (at most) in a segmented memory implementation.
I mean, when people talk about segmented memory, what most everyone
today thinks of is the x86 model, where all of this certainly is true.
So, by this definition, it would be very wrong to call what the PDP-11
have segmentation. And I would suspect that to be the reason why DEC
changed their terminology. Segmentation simply started to become an
established term, and it did not match what the PDP-11 did, so the
documentation had to change to better describe what it was.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
next prev parent reply other threads:[~2018-04-28 10:41 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-28 0:19 Noel Chiappa
2018-04-28 10:41 ` Johnny Billquist [this message]
2018-04-28 12:19 ` Rico Pajarola
[not found] <mailman.1.1525744802.16322.tuhs@minnie.tuhs.org>
2018-05-08 22:39 ` Johnny Billquist
-- strict thread matches above, loose matches on Subject: below --
2018-05-07 15:36 Noel Chiappa
2018-05-06 13:07 Noel Chiappa
2018-05-06 15:57 ` Johnny Billquist
2018-05-05 13:06 Noel Chiappa
2018-05-05 20:53 ` Johnny Billquist
2018-05-03 11:39 Noel Chiappa
2018-05-03 21:22 ` Johnny Billquist
2018-04-30 15:05 Noel Chiappa
2018-04-30 16:43 ` Paul Winalski
2018-04-30 21:41 ` Johnny Billquist
2018-05-03 2:54 ` Charles Anthony
2018-04-28 20:40 Noel Chiappa
2018-04-29 15:37 ` Johnny Billquist
2018-04-29 16:34 ` Steve Nickolas
2018-04-29 16:48 ` Warner Losh
2018-04-27 23:01 Noel Chiappa
2018-04-27 23:10 ` Johnny Billquist
2018-04-27 23:39 ` Warner Losh
[not found] <mailman.1.1524708001.6296.tuhs@minnie.tuhs.org>
2018-04-27 22:41 ` Johnny Billquist
2018-04-26 1:53 Noel Chiappa
[not found] <mailman.143.1524696952.3788.tuhs@minnie.tuhs.org>
2018-04-25 23:08 ` Johnny Billquist
2018-04-25 22:55 Noel Chiappa
[not found] <mailman.139.1524690859.3788.tuhs@minnie.tuhs.org>
2018-04-25 22:54 ` Johnny Billquist
2018-04-25 22:46 Noel Chiappa
[not found] <mailman.137.1524667148.3788.tuhs@minnie.tuhs.org>
2018-04-25 21:43 ` Johnny Billquist
2018-04-25 22:24 ` Johnny Billquist
2018-04-26 5:51 ` Tom Ivar Helbekkmo
2018-04-25 22:37 ` Johnny Billquist
2018-04-24 7:10 Rudi Blom
[not found] <mailman.125.1524526228.3788.tuhs@minnie.tuhs.org>
2018-04-23 23:44 ` Johnny Billquist
2018-04-23 23:57 ` Steve Nickolas
2018-04-24 0:24 ` Ronald Natalie
2018-04-24 0:25 ` Warren Toomey
2018-04-24 0:31 ` Dave Horsfall
2018-04-24 1:02 ` Lyndon Nerenberg
2018-04-24 4:32 ` Grant Taylor
2018-04-24 4:49 ` Bakul Shah
2018-04-24 4:59 ` Warner Losh
2018-04-24 6:22 ` Bakul Shah
2018-04-24 14:57 ` Warner Losh
2018-04-24 6:46 ` Lars Brinkhoff
2018-04-23 22:01 Noel Chiappa
2018-04-23 22:09 ` Warner Losh
2018-04-23 18:41 Noel Chiappa
2018-04-23 19:09 ` Clem Cole
2018-04-23 23:01 ` Dave Horsfall
2018-04-23 23:49 ` Dave Horsfall
2018-04-24 0:26 ` Ronald Natalie
2018-04-22 18:06 Norman Wilson
2018-04-20 16:45 Noel Chiappa
2018-04-20 16:53 ` Charles Anthony
2018-04-20 17:16 ` William Pechter
2018-04-20 23:35 ` Dave Horsfall
2018-04-22 11:48 ` Steve Simon
2018-04-20 15:02 Tim Bradshaw
2018-04-20 15:58 ` Clem Cole
2018-04-20 16:00 ` David Collantes
2018-04-20 16:12 ` Dan Cross
2018-04-20 16:21 ` Clem Cole
2018-04-20 16:33 ` Warner Losh
2018-04-20 19:17 ` Ron Natalie
2018-04-20 20:23 ` Clem Cole
2018-04-20 22:10 ` Dave Horsfall
2018-04-22 17:01 ` Lars Brinkhoff
2018-04-22 17:37 ` Clem Cole
2018-04-22 19:14 ` Bakul Shah
2018-04-22 20:58 ` Mutiny
2018-04-22 22:37 ` Clem cole
2018-04-22 21:51 ` Dave Horsfall
2018-04-25 1:27 ` Dan Stromberg
2018-04-25 12:18 ` Ronald Natalie
2018-04-25 13:39 ` Tim Bradshaw
2018-04-25 14:02 ` arnold
2018-04-25 14:59 ` tfb
2018-04-25 14:33 ` Ian Zimmerman
2018-04-25 14:46 ` Larry McVoy
2018-04-25 15:03 ` ron minnich
2018-04-25 20:29 ` Paul Winalski
2018-04-25 20:45 ` Larry McVoy
2018-04-25 21:14 ` Lawrence Stewart
2018-04-25 21:30 ` ron minnich
2018-04-25 23:01 ` Bakul Shah
2018-04-23 16:42 ` Tim Bradshaw
2018-04-23 17:30 ` Ron Natalie
2018-04-23 17:51 ` Clem Cole
2018-04-23 18:30 ` Ron Natalie
2018-04-25 14:02 ` Tom Ivar Helbekkmo
2018-04-25 14:38 ` Clem Cole
2018-04-23 20:47 ` Grant Taylor
2018-04-23 21:06 ` Clem Cole
2018-04-23 21:14 ` Dan Mick
2018-04-23 21:27 ` Clem Cole
2018-04-23 22:07 ` Tim Bradshaw
2018-04-23 22:15 ` Warner Losh
2018-04-23 23:30 ` Grant Taylor
2018-04-24 9:37 ` Michael Kjörling
2018-04-24 9:57 ` Dave Horsfall
2018-04-24 13:01 ` Nemo
2018-04-24 13:03 ` Arthur Krewat
2018-04-23 23:45 ` Arthur Krewat
2018-04-24 8:05 ` tfb
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