IIfx SIMMs; Was: Re: Tristate Buffer Output if Input is High-Z?

You are unlikely to ever see a IIfx that actually implements parity. It was an option for the IIfx but was very rare in practice. In virtually all cases the IIfx uses an 8 bit 64 pin SIMM with no parity. The presence of parity on the SIMM will not affect operation, because on a non-parity IIfx, the SIMM pins for parity connections are NC. A IIfx SIMM built for parity will have 1/8 more capacity. The extra storage for parity is on each individual SIMM. The pinout for the SIMMs is in "The Guide to the Macintosh Family Hardware". It's one of those Addison Wesley books. I don't have that particular datasheet on hand. But if you get one, I'd like a copy as well. I imagine it's a pretty standard 1M X 1 DRAM chip. I think you misread that somehow. The tech note states that the IIfx does not support 256KB SIMMs. It gives examples of memory configurations up to 32 MB, using 4 MB SIMMs, although there's a consistent typo in the example where megabit is written instead of megabyte. But the maximum memory capacity is 128 MB, using eight 16 MB SIMMs. That was/is the maximum capacity for most of the Mac II family. The exceptions are the original Mac II (68020 based), the Mac IIsi (supports 16 MB SIMMs, but only has 4 slots) and the abomination with variations known as the IIvi and IIvx. As far as I know, there can't be 30 pin SIMMs with capacities larger than 16 MB, because there are only 12 address pins available and 12 X 2 = 24 and 24 address bits yields 16M addresses. There aren't any NC pins left to convert to additional address lines, unless one steals the parity pins. Jeff Walther