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Memory upgrade for STs which breaks the 4Mb barrier, Derryck
Croker tools up for the job...
We've always been told ST TOS versions and the ST's Memory Management
Unit (MMU) cannot handle more than 4Mb but it seems the increasing
system requirements of newer applications has driven developers to come
up with a solution.
Mission impossible
So how does the Magnum card work? The cunning solution has overcome both
obstacles as follows:
- The existing TOS ROMs can be replaced with TOS 2.06 which supports
memory above 4Mb - by simply plugging ROMs into slots provided on the
Magnum card.
- Alternatively you can use MagiC v5.11 or later because it supports
memory above 4Mb - in which case you do not need to upgrade TOS as well.
- The Magnum card includes a supplementary MMU which manages memory
above 4Mb - the original MMU carries on managing your existing memory.
Installation
If your processor is already socketed it couldn't be easier. Plug the
processor into the Magnum card then plug the Magnum into the empty
processor socket - ideal for anyone who has already installed an
accelerator! Aixit claim Magnum is compatible with the HBS 240/640 and
the PAK accelerators, my AdSpeed accelerator didn't work.
If your processor is soldered to the motherboard you have two options:
- Solder a socket directly on top of the processor and plug the
Magnum into that.
- Remove the processor and fit a socket to the motherboard then
plug in the Magnum card and processor. If you ever plan to add an
accelerator this is the best option.
Unless you intend to use MagiC exclusively there's a cable to be
soldered. The installation guide includes diagrams for the various
models but these could be a lot clearer. The connection has to be
made to a PCB track connecting to the GLUE chip pin 19, apparently
the ROM 2 signal from this pin is also present on the TOS ROM
chips U4 and U7 pin 20 which might be easier to locate - check
this carefully before soldering!
![[Screenshot not available - sorry!]](grabs/** Photo 3 here **)
Check your board carefully for the ROM 2 signal
PS/2 memory Single Inline Memory Modules (SIMMs) are used offering a
maximum of 14Mb plus two non-contiguous 512Kb blocks (see boxout).
Currently STe machines are not supported - but Aixit are working on it.
Existing upgrades
![[Screenshot not available - sorry!]](grabs/** Photo 2 here **)
I've used IC sockets to space the MagnumST board above the MMU.
I've used another socket to space the 68000 processor above the
TOS 2.06 chips, one of which can be seen poking out. This
"skyscraper" fits in my Tower case
I'd recommend retaining any memory upgrade already fitted because ST
memory is sometimes required. For example, the DMA system driving the
Atari SLM laser printers requires at least 1Mb. Also, apart from the HBS
640 accelerator, which can cache up to 8Mb of TT RAM, most accelerators
only cache ST RAM.
However, if your existing memory upgrade includes a connector/PCB which
pushes onto the MMU socket you may find the Magnum SIMM hits the
connector/PCB and you have a choice to make:
- Retain the ST memory and use CPU sockets as spacers to clear the MMU
and recase the computer/keyboard if necessary.
- Remove your existing memory upgrade, accept the limitations of less ST
memory, and avoid having to recase your computer/keyboard.
![[Screenshot not available - sorry!]](grabs/** Photo 1 here **)
The ribbon cables at the left edge of the MagnumST board indicate
the position of the MMU connector/PCB below the SIMM
POKEing about
A disk is supplied which includes various utilities and documentation.
The most important one is a small AUTO folder program which tells
TOS/MagiC to see the Magnum memory as TT RAM. A utility is provided to
modify program headers so they are set to "Run in TT RAM" and "Malloc
from TT RAM". Another utility is used to select between a thorough,
quick, or no memory check at all - and the memory check can be skipped
by pressing the [Space] bar. TT RAM is sometimes referred to as
"Fast-RAM" but the Magnum card accesses all memory at the same speed as
ST RAM, i.e. 8MHz. Apart from some other useful looking utilities on the
disk there's also a text file which hints at the possibility of burning
both MagiC and TOS 2.06 into a single pair of EPROMs - interested?
I was experiencing problems loading files from floppy disks under MagiC
but this was a bug in MagiC which is now fixed (MagiC 5.11 or later).
The CDROM driver ExtenDOS Pro also required a small tweak to its
configuration file but apart from that the extra memory seems to be
highly compatible and completely transparent in use.
Finally, I'd like to thank Peter West of the TransAction crew for
translating the installation disk and my questions to Aixit.
EXPANSION OPTIONS
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ST RAM TT RAM Total
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1 4 5
1 8 9
1 16 11/14# + 1##
2 4 6
2 8 10
2 16 12 + 1##
4 4 8
4 8 12
4 16 14 + 1##
# 14Mb only possible after making an additional modification
## 1Mb available as 2x512Kb upper memory blocks.
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