OK... answering to myself, the 660AV is limited to 16 MB per bank.
Apple says that in order to reach 68 MB, you need to use 16 MB RAM chips.... like two 16 MB chip per SIMM. I don't get that. I think Apple documentation has a typo, they talk about 16 Mbits chips, not 16 Mbytes.
The 8 x OKI chips (MD51V65405) on the SIMM are 8 Mb each (4 Mb x 4) for the correct total of 64 MB, but PD2 is not grounded.... why ?
OK my head is exploding, to I'm tired. Anyone would have an idea ?
Apple's talk about megabits per chip is detailed talk about the exact way the machine addresses memory. Without understanding all about RAS and CAS and how memory is addressed, that's not going to mean much to you. I typed a very detailed explanation once. I have no idea where. Probably on MacGurus when went down...
Simpler:
72 pin SIMMs can have from one to four banks, although more than 2 is almost never seen in practice. Each bank is like a separate SIMM on the same SIMM.
The AV Quadras have a memory arrangement very much like the 7100 and 8100.
Anyway, all those machines, AVs, 7100, 8100 only have enough Address lines in the SIMM slots to support 16MB of memory per bank.
Your 64 MB SIMMs only had one bank, so the most the 660AV could see was 16 MB per SIMM.
32 MB SIMMs are typically made out of two 16 MB banks and the AV Quadras support 2 banks per SIMM.
So the max memory in the 660AV is 2 SIMMs X 2 banks X 16 MB = 64 MB + 4 MB on motherboard. In other words, 2 X 32 MB SIMMs + 4 MB motherboard = 68 MB total.
