A proof-of-space is a piece of data that a prover sends to a verifier to demonstrate that the prover has reserved a certain amount of space. In order to be practical, the verification process must be efficient, that is, it must take up little space and time.

(PoS) or called Proofs of space are similar to proofs of work (PoW), except that storage is used to earn cryptocurrency rather than computational power. Proof-of-space functions differ from memory-hard functions in that the bottleneck is the amount of memory required, rather than the number of memory access events.

While Proof-of Space-time (PoSt), as it is commonly used in relation to Filecoin, is a method by which a storage miner proves that they are still storing a unique piece of data for the network. PoSt means that anyone can now guarantee that they are using a specific amount of space on their storage.

The creators of proof-of-spacetime, Tal Moran and Ilan Orlov, refer to this as the "Rational' Proofs of Space-Time because the true cost of storage is proportional to the product of storage capacity and time that it is used.

Cryptocurrencies that use PoS

Although Bitcoin has become the most successful cryptocurrency ever, and its most distinguishing feature is its decentralized nature. The basic protocol (Nakamoto's consensus) accomplishes this through the use of proof of work(PoW), with the disadvantage that massive amounts of energy are required to keep the ledger. Furthermore, the dynamics of Bitcoin mining have slowed over time. That’s why there are cryptocurrencies that have been built to solve this problem by using proof of space or PoST.

PoS is also similar to Proof of Capacity (PoC) which is a blockchain network consensus mechanism algorithm that allows mining devices in the network to use their available hard drive space to decide mining rights and validate transactions. This is in contrast to using the computational power of the mining device as in the proof of work algorithm or the miner's stake in the cryptocurrencies as in the proof of stake algorithm.

Chia Network

Chia’s new innovative Nakamoto consensus algorithm removes the energy demands of Proof of Work (PoW) from the system, making it as energy efficient as possible.

Proof of space can be demonstrated if you have some memory or disk space on your hard disk drive (HDDs) or solid-state drives (SSD) that are not being used

Read Chia Green Paper.

FileCoin

Filecoin is a protocol token whose blockchain employs a novel proof known as Proof-of-Spacetime, in which blocks are created by miners who store data.

The Filecoin protocol is a blockchain-based Decentralized Storage Network with a native token. DSNs aggregate storage ordered from multiple independent storage providers and self-coordinate to provide clients with data storage and retrieval.

Read FileCoin White Paper

SpaceMint

SpaceMint, formerly known as Spacecoin (SPACE), is a cryptocurrency that uses the Proofs of Space protocol. Proof-of-space (PoSpace) protocols allow SPACE miners to be rewarded for dedicating disk space rather than dedicating computational power as in proof-of-work protocols.

SpaceMint's proof-of-space (PoSpace) protocol rewards small miners disproportionately in order to encourage miner participation and decentralization of the SpaceMint network. When compared to proof-of-work networks, miners on the SpaceMint network spend a fraction of a second per mined block and use significantly less energy on ledger maintenance.

Read SpaceMint White Paper

BurstCoin(Now Signum)

Proof of capacity implementation in Burstcoin generates random solutions, also known as plots, in advance and stores them on hard drives using the Shabal cryptographic algorithm. This stage is known as plotting, and it can take days or even weeks depending on the drive's storage capacity. In the next stage, mining, miners match their solutions to the most recent puzzle, and the node with the quickest solution wins the right to mine the next block.

Read BurstCoin White Paper