Proof-of-space

Proof-of-space (PoSpace), also called Proof-of-capacity (PoC), is a means of showing that one has a legitimate interest in a service (such as sending an email) by allocating a non-trivial amount of memory or disk space to solve a challenge presented by the service provider.wikipedia
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Proof-of-work system

proof-of-workproof of workreusable proof of work
Proofs of space are very similar to proofs of work, except that instead of computation, storage is used.
Proof of space (PoSpace) proposals apply the same principle by proving a dedicated amount of memory or disk space instead of CPU time.

Cryptocurrency

cryptocurrenciescrypto-currencyaltcoin
After the release of Bitcoin, alternatives to its PoW mining mechanism were researched and PoSpace was studied in the context of cryptocurrencies.

Graph pebbling

hard-to-pebble graphs
One way of implementing PoSpace is by using hard-to-pebble graphs.

Client Puzzle Protocol

client puzzlecomputation-based puzzle protocols
Proofs of space could be used as an alternative to proofs of work in the traditional client puzzle applications such as anti-spam measures and denial of service attack prevention.

Trusted Computing

remote attestationattestationcurtained memory
Proof of space (PoS) have been proposed to be used for malware detection, by determining whether the L1 cache of a processor is empty (e.g., has enough space to evaluate the PoSpace routine without cache misses) or contains a routine that resisted being evicted.

POC

Proof-of-capacity, an algorithm used to mine the Burstcoin digital cryptocurrency

Proof of secure erasure

Proof of space is a protocol similar to proof of secure erasure in that both require the prover to dedicate a specific amount of memory to convince the verifier.