@lynn @fae Even so... Most cards other than 8080 CPU cards had their main power draw on the +5V rail. Notable exceptions were dynamic RAM cards using 4K or 16K DRAMs, which drew a lot of current from the +16V (+13.5V IMSAI) rail. I could see having a 22-slot backplane full of fancy cards that each drew perhaps 3A of +8V. AFAIK, no stock S-100 chassis had a power supply that could handle that, nor could any stock backplane, and you'd need extra cooling fans blowing over the cards.