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From: jeroen@plato.phil.ruu.nl (Jeroen Scheerder)
Newsgroups: comp.sys.atari.st
Subject: 3 MB - Yessir! (pt. 1)
Message-ID: <586@accucx.cc.ruu.nl>
Date: 24 Jul 90 11:51:14 GMT
Sender: news@accucx.cc.ruu.nl
Reply-To: jeroen@plato.phil.ruu.nl (Jeroen Scheerder)
Organization: Logic section, Department of Philosophy, Utrecht
Lines: 73


In article <1990Jul23.135351.4486@diku.dk>, jensting@rimfaxe.diku.dk (Jens Tingleerd
writes:
|>jeroen@plato.phil.ruu.nl (Jeroen Scheerder) writes:
|>
|>>In article <5223@castle.ed.ac.uk>, tj@castle.ed.ac.uk (T Jones) writes:
|>[..]
|>>I was the one posting about the 3.0 Mb modification; however, having read the
explaining it all (it's from a German magazine, I think it's
|>>called 'ST Magazin' or something) I decided I would let someone more experien
work for me.
|>>Looking in my computer I see 2 SIMMs, and a *LOT* of wire.
|>
|>I, for one, doubt that you are *at all* able to make the ST use 3.0 MB. There
|>are two banks of memory, each wth either 0.5 MB or 2.0MB. That makes
|>
|>	0.5 MB		1x0.5
|>	1.0 MB		2x0.5
|>	2.0 MB		1x2.0
|>	2.5 MB		1x0.5 + 1x2.0		Not available from Atari ...
|>	4.0 MB		2x2.0
|>
|>The above calculation is based on the fact that the MMU knows about 
|>two banks, NO MORE. the nice thing ( ;-) ) is that the MMU autodetects.. .
|>
|>So, no unused 0.5 MB in a 2.5MB installation, no 3.0 MB installation
|>possible.
|>
|>Disclaimer
|>	This may not be true for STEs, I don't know.. .
|>	Do correct me if I'm wrong.
|>
|>*IF* I'm wrong, please give a reference to the relevant article.. .
|>(I have seen ads for 5.0MB extensions, where the last 1 MB was 
|>used for RAM disk, so perhaps....)
|>
|>	Jens
|>Jens Tingleff MSc EE, Institute of Computer Science, Copenhagen University
|>Snail mail: DIKU Universitetsparken 1 DK2100 KBH O
|>"It never runs around here; it just comes crashing down"
|>	apologies to  Dire Straits 
                                      
Yes - you *ARE* wrong. First: 2.5 Mb is *NO* *PROBLEM* *AT* *ALL*. Like you say,
0.5-Mb bank go nicely together. The mere fact that Atari ships no 2.5 Mb-equippe

	"
this configuration impossible. 3.0 Mb is possible too; but it really is a hack
to get around the 2 bank limit. I will describe that in the following article.

The following stuff really should be put in the 'tech' newsgroup, but I started 
request to Dave Small ... anyway, here it is.

My ST *DEFINITIVELY* has 3.0 Mb. I agree, not long ago I thought this impossible
the magazine "ST Computer" 3/1990 (a German magazine), the author K. D.
Litteck describes how it is done (the article is called "Aus zwei und ein halb m
German, and my German is not too good, but I'll try to describe the article
accurately.

How does it work? Well after determining memory configuration (see below) TOS st
amount of memory it thinks is available. Say you've got 3.0 Mb available
(like I do); TOS at first thinks 2 banks of 2 Mb are available and sets out to c
then runs into nonexistent memory when it reaches the end of the three
available megabytes. En exception occurs of type buserror occurs, at which is de
adress the error occurred. This adress is then written in the TOS variable
phystop, thus setting the correct memory size. Now TOS boots on ...
This works like this in all TOS versions known to mankind.

For technical details see part 2 of this posting.


	"Talking about Math can almost be as satisfying as the real thing,
	 and not half so risky."
				cf. 'The Bluffer's Guide to Bluffing'