You're talking about a II board with a MC68851 PMMU chip in em, since these are hard to find. I used to have one but sold it. The chip replaced the HMMU Hochsprung MMU chip that simply bridged 24 to 32 bitness. the PMMU allowed Virtual memory to be used, and contained a root table pointer to a tree of logical to physical address translations that were requested by the CPU, and a cache of some of these. if youre interested I might be able to track one down.