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Acorn Archimedes at 25 feature on the Register

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Liam Proven

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Jun 1, 2012, 10:34:34 AM6/1/12
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This is not one of mine, BTW - not engaging in blatant self-promotion, for once!

http://www.reghardware.com/2012/06/01/acorn_archimedes_is_25_years_old/

Grahame Parish

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Jun 1, 2012, 11:47:09 AM6/1/12
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On 01/06/2012 15:34, Liam Proven wrote:
> This is not one of mine, BTW - not engaging in blatant self-promotion, for once!
>
> http://www.reghardware.com/2012/06/01/acorn_archimedes_is_25_years_old/
>
Great article. Not sure about MEMC being able to address 32MB and
implementing virtual memory via disc though...

Grahame.

Theo Markettos

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Jun 1, 2012, 12:22:33 PM6/1/12
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Grahame Parish <maillis...@millers-way.net> wrote:
> Great article. Not sure about MEMC being able to address 32MB and
> implementing virtual memory via disc though...

RISC iX had VM, didn't it? There was also 'Virtualise' on RO3.1 which was
VM of sorts.

Theo

Grahame Parish

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Jun 1, 2012, 12:43:43 PM6/1/12
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It was more about the following paragraph at the bottom of page 2: -

"Novelly, the MEMC memory controller – 'Anna' – was able to support 32MB
of memory – far more than it was economically feasible to add, so it was
able to page the 4MB of physical Ram on and off a hard drive to provide
rudimentary virtual memory, something we take for granted today. Ditto
the application memory protection, a feature modern multitasking
operating systems manage for their users."

I'm seem to remember MEMC addressing only 4MB as you needed two MEMCs
for an 8MB upgrade.

Grahame.

jgharston

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Jun 1, 2012, 1:23:40 PM6/1/12
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Grahame Parish wrote:
> "MEMC ... was able to support 32MB of memory"
>
> I'm seem to remember MEMC addressing only 4MB as you needed two MEMCs
> for an 8MB upgrade.

I think.... you could have a maximum of 8 MEMCs. 8x4M = 32M. Whether
you could physically have 8 MEMCs would depend on the PCB and the
wiring.

or... and this feels more likely, the MEMC maps the physical memory
into a 32M logical memory map. That could be what the Register
article is actually talking about.

The technical reference manual isn't initially illuminating.

JGH

Theo Markettos

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Jun 1, 2012, 2:42:59 PM6/1/12
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jgharston <j...@arcade.demon.co.uk> wrote:
> I think.... you could have a maximum of 8 MEMCs. 8x4M = 32M. Whether
> you could physically have 8 MEMCs would depend on the PCB and the
> wiring.
>
> or... and this feels more likely, the MEMC maps the physical memory
> into a 32M logical memory map. That could be what the Register
> article is actually talking about.

The memory map goes like this:
00000000-01FFFFFF: 32MB logical RAM
02000000-02FFFFFF: 16MB physical RAM
03000000-033FFFFF: I/O
03400000-03FFFFFF: ROMs (read mode)
03400000-035FFFFF: VIDC (write mode)
03600000-037FFFFF: MEMC (write mode)
03800000-03FFFFFF: logical to physical addressing tables (write mode)

So you could have 16MB physical RAM (4 MEMCs, via some cunning multiplexing
logic) and that could appear in 32MB of logical address space. The
limitation of 4MB per MEMC was the logical to physical address tables -
that's why the page size on a 4MB machine grows to 32KB, because there's a
fixed number of pages but the page size can be changed.

Theo

druck

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Jun 2, 2012, 2:55:53 PM6/2/12
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A MEMC1 could only access 4MB, but the A540 could have another 3 cards
each containing a MEMC and 4MB of RAM.

Risc iX was a unix variant, so could do VM via disc, but there was also
a very hacky system for RISC OS at one point. It was incredibly slow
with an ST506 disc, but it did enable things to be done that wouldn't
otherwise be possible.

---druck

Rick Murray

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Jun 2, 2012, 5:41:48 PM6/2/12
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On Fri, 01 Jun 2012 17:43:43 +0100, Grahame Parish
<maillis...@millers-way.net> wrote:

> I'm seem to remember MEMC addressing only 4MB as you needed two
MEMCs
> for an 8MB upgrade.

It is a little garbled due to not following the addressing scheme.

The nominal memory map was 64Mb, the most a 26 bit PC+PSR setup could
handle. Of that, 32Mb was physical memory, mapped into the other 32Mb
in a variety of ways (some is hardware/IO, etc). This might seem
wasteful/silly, but it is because these were crazy sizes back then.
Which explains why one individual MEMC is only capable of addressing
4Mb (so, yes, two in tandem for 8Mb).

I see this, and I see a little moving-eyeballs-on-the-desktop program
(under Windows) claim itself a mere 14Mb, and I cry...


Talking of crying, I read this article, I realised the ARM is
essentially a quarter century old, and my hair did a Leland Palmer
(there's another old reference for you, though that's only 22 years
old).


Best wishes,

Rick.

Rick Murray

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Jun 2, 2012, 5:44:44 PM6/2/12
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On Sat, 02 Jun 2012 23:41:48 +0200, Rick Murray
<heyrickma...@yahoo.co.uk> wrote:

> handle. Of that, 32Mb was physical memory, mapped into the other
32Mb
> in a variety of ways (some is hardware/IO, etc). This might seem

Correction - I think it is 32Mb mapped memory, which would imply 16Mb
actual memory, and 16Mb "other stuff" (ROMs, VIDC, I/O, blah blah).

Something like that. There's a datasheet around. I still feel old...


Best wishes,

Rick.

patric aristide

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Jun 2, 2012, 7:24:37 PM6/2/12
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On 2012-06-02, Rick Murray <heyrickma...@yahoo.co.uk> wrote:
>
>
> Talking of crying, I read this article, I realised the ARM is
> essentially a quarter century old, and my hair did a Leland Palmer
> (there's another old reference for you, though that's only 22 years
> old).
>

22yrs, blimey! Still call my now ARM based tape recorder "Diane"

Patric
--
GL

Dave Higton

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Jun 3, 2012, 8:57:13 AM6/3/12
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In message <slrn3vfsjsl...@odin.sdf-eu.org>
patric aristide <ti...@sdf-eu.org> wrote:

> my now ARM based tape recorder

What is that?

Dave

patric

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Jun 3, 2012, 11:08:16 AM6/3/12
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On Sun, 03 Jun 2012 14:57:13 +0200, Dave Higton <da...@davehigton.me.uk>
wrote:
My (dicta)phone

patric

Dave Symes

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Jun 3, 2012, 1:09:34 PM6/3/12
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In article <op.wfb1n...@medion-pc.fritz.box>,
And to finish an old joke...

Don't be so dirty, use your finger like everyone else. ;-)

D.

--

Dave Triffid

Philip Green

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Jun 10, 2012, 4:21:37 AM6/10/12
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My son and I used to take turns racking up an ever higher high score on
!Tetris but it ended up going too fast for me until I hit upon the idea of
starting a couple of concurrent animations of a spinning cube. That ate up
enough processing power to slow down the !Tetris sufficiently for me to add
about 50% to our previous high score which he then discovered when he got back
from school.
I still don't know whether he ever found out how I did it.

jgharston

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Jun 11, 2012, 1:55:15 PM6/11/12
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Rick Murray wrote:
> Talking of crying, I read this article, I realised the ARM is
> essentially a quarter century old, and my hair did a Leland Palmer

I was discussing some Z80 code I wrote "some time ago" with
sombody, pointing out my horrible coding style back then,
then mentally tripped over my own feet when I realised that
1984 (when I wrote it) is 28 years ago. Eek!

Must update my CV. "...nearly 30 years' experience..." ;)

JGH
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