An application-specific integrated circuit (abbreviated as ASIC) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. In Bitcoin mining hardware, ASICs were the next step of development after CPUs, GPUs and FPGAs. The main thrust of this document is that proof-of-work schemes ought to be as simple and dependent on raw computational power as possible. That is, a proof-of-work should tend toward the thermodynamic limit (see a later section for this term) as quickly and directly as possible.