I recently purchased several S-100 boards from eBay; the prices were good and I figured one of these days I’ll find some documentation for them, or I’ll have the time to chase signals enough to figure out what they do. One looks like an old Winchester MFM or RLL drive board, given the connectors and the number of pins. Another resembles some sort of IDE adapter board. All are by manufacturers with little or no information available. Makes things interesting, I guess. Also have an Alpha Micro AM-919 backplane with lots of slots. Not currently hooked up, still sitting in the shipping box, but should be handy one of these days. Hopefully I’ll come across a set of drawings for it, just to make sure everything is wired the way my smaller AM board is.