Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!snorkelwacker!bloom-beacon!eru!luth!sunic!mcsun!hp4nl!ruuinf!piet
From: piet@cs.ruu.nl (Piet van Oostrum)
Newsgroups: comp.sys.atari.st
Subject: Re: 3.0mb ST bin
Message-ID: <3651@ruuinf.cs.ruu.nl>
Date: 27 Jul 90 11:36:47 GMT
References: <5223@castle.ed.ac.uk> <581@accucx.cc.ruu.nl>
Sender: news@ruuinf.cs.ruu.nl
Reply-To: piet@cs.ruu.nl (Piet van Oostrum)
Organization: Dept of Computer Science, Utrecht University, The Netherlands
Lines: 52
In-reply-to: jeroen@plato.phil.ruu.nl (Jeroen Scheerder)

Please note that I am not the author of the following article. The author
had some problems posting, so I did it for him. Replies should be made to:

jeroen@phil.ruu.nl (Jeroen Scheerder)


Due to manifold requests (since my original posting was badly formatted - I
usually post things from xrn, which apparently has a weird editor) this article
is reposted in an edited version. This article is a general introduction,
technical details of the matter are now posted to the ..tech newsgroup, along
with the schematics.

In article <1990Jul23.135351.4486@diku.dk>, jensting@rimfaxe.diku.dk
(Jens Tingleff) writes:
|>
|>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.
|>
|>*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
                                      
Yes - you *ARE* wrong. First: all those people who used to have 2 banks of
0.5 Mb, and who upgraded to 2.5 Mb have 'switched off' one of the 0.5 banks
in order to be able to use this bank for 1 Mbit chips, thus creating a 2.0
Mb bank. Totally expanding a 1 Mb ST with 2 Mb gives you a 2.5 Mb ST, and
one unused 0.5 Mb bank. Article: "Aus zweieinhalb mach drei", by K.-D.
Litteck, in ST Computer 3/1990 (published by Heim Fachverlag in Germany).
(plus: a correction to the schematic in this article in the same magazine,
issue 4/1990).

Now using the inactive 0.5 Mb thus resulting in a total of 3.0 Mb is possible
too; it really is a hack to get around the 2 bank limit. I will describe
how this is done in the article series in the ...tech newsgroup.

Enjoy!

		Jeroen.