At 10:36 -0400 04/16/2005, Michael wrote:
>Hello,
>
>>  The NVRAM is a separate SRAM chip which has an 8KB capacity.  Apple
>>  used several different pin compatible SRAM chips for this
>>  application, from such manufactures as Sony, Samsung and Winbond.
>>  The NVRAMRC file is stored in NVRAM and some other things.
>>
>>  So PRAM and NVRAM reside in physically separate chips, and they are
>>  used to store different items, although I don't know which items go
>>  where in any kind of detail.
>>
>>  I've tried replacing the 8K chip with a 32KB pin compatible chip, and
>>  the machine works as before, but it still only sees 8KB of NVRAM.  I
>>  guess the address space is built into the firmware or the wireing of
>>  the interface to the NVRAM chip.
>
>Hmm, I remember some UMAX docs saying that one of the differences
>  between the PM9500 and the S900 was that the latter had twice the amount
>  of NVRAM. Since they used vanilla OF 1.0.5 as it came from Apple ( as far as
>  I know they weren't allowed to mess with it which resulted in some annoying
>  weirdnesses  ) so either there's a way to use more than 8KB or they just got
>  16KB chips cheaper than 8KB ones.

The Umax motherboards I have here have 8K chips on board.  But there 
is a second set of pads for a different chip package in the same 
space as the pads that are used for the 8K chips.  It is possible 
that the Umax engineers installed or planned to install16K NVRAM 
chips at first until they realized or discovered that it would make 
no difference.

Jeff Walther