8mb on 68000

[barana]

does anyone know of a way to hack a 68000 mac - esp a compact to use 8mb ram? has it been done?

thx I3arana.

 

[Trash80toHP_Mini]

The only 68000 Macs to do that natively were the PB100 (8MB) and the Luggable (9MB), AFAIK.

Several accelerators had expansion memory slots and addressed the additional RAM using Compact Virtual, IIRC.

 

[bbraun]

More than 4MB of RAM bumps up against the ROM address space in these machines, which is ultimately the limiting factor.

Additionally, SCSI sits in the middle of a relatively large hole in the address space above ROM. For 128k through 512ke machines it would be reasonable to have a 5MB ROM though.

The portable and pb100 are the exceptions because their ROM was located elsewhere.

 

[Macdrone]

Accelerators on SE and better that accept ram and with virtual software allow more useable ram. I have an SE with 12 mb I think it is. Ill boot it up Monday when I get home and takeaway screen shot.

 

[MinerAl]

Would this software for more RAM work with a 512ke with an upgrade card and 6M? Supposedly the 2M extra can be used as a RAM disk, but I don't have the software for that either. What is the name of the software you speak of?

 

[Trash80toHP_Mini]

"compact virtual" macintosh "virtual memory"

First Hit: http://www.micromac.com/products/compact_virtual.html

 

[barana]

gamba has it.

I'm a bit of a 68000 purist. I dont want to upgrade my 68000 machines above a 68000. 040's are just as easy to buy. and with a 68000,I think you're stuck with 4mb, yeah?

 

[Macdrone]

My SE accelerator is a 68000 but just faster at 20 MHz or 12 I forget. I have the box, when I get home ill look.

 

[barana]

Very interested, Macdrone.

 

[MinerAl]

Trash - I thought we were talking about software for accessing more than 4M of physical RAM attached via accelerator/expansion cards.

 

[barana]

@Mineral

Not exclusively, I asked for any way it has been done, preferably with a 68000 is _my_ goal I was thinking along the lines of extra chips or memory expansion Board hack, with altered software to suit.

But thats why I asked questions. Im not only asking what has traditionally Been done, but what other ways it has been done. A case in point of what I deikne as a hack is the scsi ramdisk somone has soldered up recently or say piggybacking chips with some software to match

 

[Macdrone]

I don't know the hack styles but third party accelerators and the Connectix virtual software 3.0.2 allow more than 4 Mbs of ram with also maintaining the same 68000 processor.

 

[barana]

Conntix virtual requires an 020 +

 

[Trash80toHP_Mini]

@ MinerAl: Yep, I was as well. "Compact Virtual" would be the key to unlock the SIMMs on all such accelerators.

I imagine CV requires a 68020 with the PMMU upgrade at a minimum, VM doesn't work w/o paged memory capability, IIRC.

I3arana, check to see if you can turn off acceleration while leaving the RAM/VM active on any of the SE/Killy Klip Accelerators.

Then you could consider the upgrade a RAM Disk/VM Co-Processor Card and remain 68000 correct for your Cube! }

 

[Dog Cow]

does anyone know of a way to hack a 68000 mac - esp a compact to use 8mb ram? has it been done?

The 16 MB address space of the MC68000 is divided into four equal regions of 4 MB:

- system RAM

- system ROM

- SCC I/O addresses

- IWM and VIA I/O addresses

Read Inside Macintosh and the Macintosh Family Hardware Reference for more information.

 

[barana]

thanks dogcow!, ive found a really good resource on linux m68 for mac site

im also delving into the details on the 52c80 scsi chip and its implementation on the plus&pb100. very interesting.

im erring towards the powerbook 100 sofar, as it seems to have 8mb of system ram available.... which is kinda cool.

for a ramdisk im thinking I will build the avr scsi ramdisk that is floating around the net, but bumping the ram upto 700mb with 72pin simms.