Proof of Work (PoW)

Proof of Work requires miners to solve a computationally expensive puzzle — finding a nonce such that the block hash is below a target value. The difficulty adjusts automatically to maintain a consistent block time. PoW's security comes from the enormous cost of computation: attacking the network requires controlling 51% of the total hash power. Bitcoin uses PoW with SHA-256. While extremely secure, PoW has drawbacks: high energy consumption, mining centralization in regions with cheap electricity, and relatively slow transaction throughput.