Proof of Work is a key principle underlying blockchain technology. In most blockchain systems, PoW is a piece of information which is hard to get but easy for others on the network to verify and which also follows the network’s rules. PoW requirements force miners to conduct expensive computations in order to facilitate transactions on the blockchain. The computations are expensive in the sense that they are costly in terms of time, hardware and energy. The expense involved in PoW is compensated by paying miners in cryptocurrency coins. PoW is very similar to PoSpace (Proof of Space), except PoSpace.