The S-100 bus was something of an industry standard in the 1970s, for 8080 and Z80 computers built on a backplane design. It was invented with the Altair 8800, which apparently provided 16 or 18 expansion slots, depending on the model. That sounds like a lot, but you tended to need all the slots you could get; memory, for example, had to be added in the form of cards containing only a few kilobytes each. Presumably S-100 computers from different manufacturers, provided different numbers of expansion slots.
What was the maximum number of cards you could put on an S-100 bus? I mean, presumably there must have been some limit, either in terms of the amount of power they would draw, or just in terms of how long the bus could be. Did some manufacturers, trying to offer very many expansion slots as a selling point, approach the limit, or was it so absurdly large that you would never get near it in practice?