What is the Proof of Capacity/ Proof of Space (PoC/ PoSpace) consensus protocol?

Proof of Capacity/ Proof of Space (PoC/ PoSpace) is a protocol that selects miners based on the amount of free space on a computer's hard drive. PoC miners do their planning by creating lists of all possible hashes. The created lists are stored on the hard drive. The number of possible solutions depends on the memory size. The more solutions the miner offers, the higher the probability of finding the right combination of hashes and getting a reward. This mechanism does not require expensive hardware, but the protocol is considered to be susceptible to hacker attacks, so it is less popular. The PoC protocol is currently used in Signum (Signa).