There was a time when the signal integrity of connections between digital ICs could be nearly ensured by following one simple rule: don’t connect more than some maximum number of input pins to any single output pin. Often the fanout limit would be around 7. No models, no simulations. Everything we needed was in the thick books of vendor datasheets that filled our shelves, the tree-killing viral precursor to AOL installation CDs. Ah, those were the days!