Our oldest key system here is built on a passive motherboard. We have always used high quality DIN 41612 connectors on every card, for reliabilty issues. The design is old ( it still uses the 8255 !) but it works and passes EMC with flying colours.

All the processor lines are buffered with LS244 gates, except RD WR and PSEN, which are buffered with LS125

The plugin cards can use any or all of the processor AD bus, as well as +/-15V analogue supplies.

The processor card can still use the 8052-AH BASIC, which shows the age of the design

The whole motherboard sits on an integrated card frame, and all the plugins are 1/2 eurocard size.

It gives us quick design flexibility, though I really ought to get rid of the 8255s before Erik finds out....
;-))
Steve