> Aren't "big" 3D circuits unfeasible due to temperature limitations, though? Less so than you'd think, since (as long as you can keep leakage current under co

> Aren't "big" 3D circuits unfeasible due to temperature limitations, though? Less so than you'd think, since (as long as you can keep leakage current under control) heat is only generated when the circuits are active (barring leakage current, when bits are being flipped). So you can have arbitrarily large amounts of increasingly-rarely-used circuitry for various purposes. The naive-but-easy-to-understand example would be having separate, optimal circuitry for each machine instruction - the total number of gates is O(N*M), but the number of gates activated on each clock cycle (and thus the amount of waste heat generated) is only O(N), so you can keep adding new, perfectly-hardware-accelerated instructions up to the limits of physical space. In practice it's more complicated and less of a nonissue, but it's not "big circuits are useful in proportion to their surface area, not their volume", it's more "big circuits are less useful than their volume alone would suggest". (You do hit physical limits like the Bekenstein bound[0] eventually, but that's far enough out that we mostly don't care yet.) 0: https://en.wikipedia.org/wiki/Bekenstein_bound https://en.wikipedia.org/wiki/Bekenstein_bound