What Proof of Space and Time proves
Proof of Space proves that a participant allocated storage. Proof of Time proves that real time passed through a verifiable delay function. Together, they let a chain select block winners without making every participant run constant energy-intensive hashing.
Chia calls this farming rather than mining. Farmers store random-looking plot data on disk, and their chance of winning is proportional to the space they dedicate to the network.
How Chia uses it
Chia's consensus documentation describes storage capacity as the scarce resource and a VDF as the mechanism that proves time elapsed. This combination is designed to make the canonical chain transparent and verifiable.
Instead of buying ASIC miners, participants allocate hard-drive space and keep their plots available. That changes the economics of participation, but it still creates real hardware, maintenance, and opportunity costs.
Chains that use Proof of Space and Time
Chia is the best-known Proof of Space and Time blockchain. Related proof-of-space and proof-of-capacity systems have appeared in storage-oriented crypto designs, but Chia is the clearest mainstream reference for PoST as a consensus model.
Readers should distinguish Chia-style consensus from Filecoin-style storage proofs. Chia uses storage to help secure consensus; Filecoin uses proofs to verify that specific client data is stored over time.
Tradeoffs readers should know
Proof of Space and Time can reduce constant electricity use compared with PoW mining, but it can still affect storage markets, hardware wear, plotting costs, and centralization if large farmers dominate available space.
A good review checks netspace distribution, farming rewards, hardware assumptions, plotting requirements, pooling, and whether storage capacity is widely distributed enough to support the security story.