ASIC hashboard

What it does

A hashboard is a long PCB carrying a chain of application specific integrated circuits wired in series. Each chip does exactly one thing: it computes double SHA-256 over a block header with a different nonce, checks whether the result falls below the target, and reports back only when it does. It cannot run anything else. It has no instruction set to speak of and no general purpose logic. That narrowness is the entire reason it is thousands of times faster per watt than a graphics card.

The chips are chained rather than parallel because the board feeds one work item across the whole string and lets each chip search a different slice of the nonce range. The controller hands down a block template, the board splits the search space, and the chips grind through it. A 78 TH/s board is testing 78 trillion candidate headers every second, and discarding effectively all of them.

Three boards is a full chain on this class of machine. Each one you add is another 78 TH/s of claim on the block, and another 1177 W of fuel you have to keep buying. The board does not care whether you can afford it.