At 11:49 -0700 05/06/2003, Henry B. Hotz wrote:
>At 2:32 PM -0400 5/6/03, kevdig@rcn.com wrote:
>>A while back someone posted a message about upgrading nvram?
>>Is this possible? If I remember correctly, the machine in
>>question was the same one I use, an 8600? Comments from
>>someone at Apple VERY welcome. Thanks!
>
>It wasn't anyone at Apple.  If I had to guess I'd say it was John 
>Klos <john@ziaspace.com>, but I could be wrong.

I think it was me.   However, the machine in question was not an 
8600, it was basically any machine in the PowerSurge family (7500 - 
9600, 7300, plus relevant clones and ANS).

What I found was that replacing the NVRAM chip with a larger capacity 
pin compatible chip does not appear to increase the NVRAM capacity. 
The NVRAM chip is a small 8K X 8 SRAM chip.  I replaced it with a 32K 
X 8 SRAM chip.

After replacement, the NVRAM still functioned properly, but as far as 
I could tell, the NVRAM capacity remained the same.   There was some 
ambiguity in my tests, as I'm not certain the method I used reported 
measured NVRAM capacity or simply reported what the software expected 
the machine in question to have.    I don't remember how I performed 
the test any more, so I can't be more specific.   I do remember that 
I thought I was testing actual NVRAM capacity and that I went through 
minor gymnastics to get around the "expected result reported" issue.

There could be a few reasons for this.  Apple may not have 
implemented the extra address lines needed to support a larger chip. 
Or the 8K SRAM chip may be mapped to an 8K space in address space and 
so is not expandable without modifying the address map, which means 
modifying the ROMs.

Anyway, the end result is that I believe that simply replacing the 
SRAM chip with one of larger capacity does not increase the NVRAM 
capacity.   This result could be mistaken, if my method of 
determining NVRAM capacity was faulty.

Additionally, it may be possible to hack the Mac ROM in order to 
cause the larger capacity chip to be "seen".   If someone can come up 
with a modified PowerSurge ROM image, I can put it on compatible 
chips and either install the chips on a motherboard, or build a ROM 
module which plugs into the ROM slot on x500 and x600 machines and 
disables the on-board ROM and uses the ROM on the module.   I can 
also do the above if someone wants to produce OF hacks or other ROM 
modifications.

I still have a supply of 32K X 8 SRAM chips, so if anyone wants a 
motherboard modified and wants to foot the shipping costs (I'm in 
Austin, TX) I would be happy to replace their SRAM chip so that they 
can experiment on it.    Or if you're capable of doing the 
replacement yourself, let me know and I can mail you a 32K X 8 SRAM 
chip.   That's much cheaper than two way shipping for an entire 
motherboard.

Jeff Walther

P.S.   (mainly to John K.) Have you made any progress on adapting a 
Mach V card to a pre-Kansas machine?