I wrote:

>>The Gestalt ID for the Quadra 605 is 94 and the Gestalt ID for the 
>>Performa 475 is 89. So at this level the two are not _exactly_ identical 
>>even if you change the faceplate.  If you dig a bit deeper into the ROMs 
>>you'll find that although the two share many common routines, they use 
>>some different sequences for ADB interrupt handling.  From a NetBSD point 
>>of view, if your Kernel is built on the MRG routines, the two systems are 
>>not _exactly_ the same, but very similar.
>
Steven responded:

>This is not true.  There's a jumper, on the Q605's logic board, that if 
>present, makes Gestalt report the machine is a Q605.  If it's missing, 
>the machine reports itself as an LC 475. These machine are _completely_ 
>identical, and use the same ROM rev, and hardware.  The only difference 
>are the nameplates, the cases and the presence of this jumper at J118. I 
>have installed this jumper on my own LC 475, to test it, and it is true.  
>Under System 7.1, my LC 475 will report itself as a Q605.
>
>This is from www.violet.berkeley.edu/q605.html:
>
>The Quadra 605, LC475, P475, and P476 use the same motherboard. A jumper 
>in the front right hand corner, J118, differentiates the Quadra 605 and 
>LC475. The Performa 475 and 476 are the same as the LC475. If the jumper 
>is installed, it is a Quadra 605. If the jumper is not, it is a LC475. 
>The system and other software know this from what is called a gestalt. 
>The gestalt is a number that is specific to each type of Mac Apple makes. 
>A Quadra 605 is gestalt 94 while a LC475 is gestalt 89. There are several 
>unassigned gestalts, and this modification will explain a few of them: 

Please re-read what I wrote. The Gestalt IDs are different. You seem to 
have agreed to that. I made no mention of the jumper because I didn't 
want to confuse the issue, but I'm well aware of the jumper.  Although 
the machines use the same ROMs, they use different parts of the ROMs 
making them non-identical as far as software is concerned - especially 
the MRG based NetBSD Kernel (which is what the original poster was having 
problem with).  If you'll investigate the structure of the ROMs (as I 
have done while working on the MRG code), you'll discover there are 
machine independent and machine dependent sections of the ROMs.  The 
Quadra 605 and LC 475 use the same machine dependent section of the ROM 
but use different parts of the machine independent section.  This makes 
them non-identical - they are not *EXACTLY* the same from a software 
point of view.  If you'd like a more detailed explaination look at the 
comments I put into the "machdep.c" module in NetBSD, check Apple's 
Machine Data Base and do some poking around in the ROMs.  A good starting 
point might be the sources for the NetBSD ROM Sniffer that I wrote in 
support of the NetBSD MRG effort. You might also try answering the 
question of why the Gestalt IDs are different on two machines you claim 
to be identical, but with some other machines the Gestalt IDs are 
identical and the underlying machine archictures are different.

-bob