At 14:12 +0200 04/15/2005, Schwerzmann, Stephan wrote:
>>  Is resetting PRAM the same as resetting NVRAM, or are they two
>>  different things?
>
>PRAM (=Parameter RAM) is apple-speak for the small memory built
>using an NVRAM (=Non Volatile RAM) technology chip for the
>purpose of storing a couple of parameters e.g. the ones relevant
>for booting and a few more
>
>NVRAM is actually a CMOS/SRAM (Static RAM) technology flavor:
>it is particularily low-power and suits applications where a
>little bunch of data is to be kept over periods of no ac power
>

In the older machines, Beige G3 and earlier, the PRAM is stored in 
the CUDA controller chip which also handles the ADB functions and 
contains the real time clock.  Certain system settings are stored 
there.  This chip is typically labeled 341S0788, although there is 
also a 341S0760 (I think) version.

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.

I don't know how the later machines (Blue & White and later) handle 
this storage.   Since they lack an ADB bus, (except the B&W) the PRAM 
probably isn't in a CUDA chip any more.

Jeff Walther