Proof of Work
Proof of Work (PoW) is Bitcoin's consensus mechanism: miners prove they spent energy by solving a cryptographic puzzle.
PoW solves the double-spend problem in decentralised systems without central authority. Miners try billions of nonces per second until they find a block hash below the target (difficulty). The winner adds the block and earns the reward. Real costs (energy + hardware) make cheating economically irrational: fraud costs more than the upside.
Example
Every block hash must be below a target (e.g. hash starts with 20 zeros). Miners vary the nonce in the header until such a hash is found. Average attempts: trillions. Statistical certainty: one success every ~10 minutes.
Frequently asked questions
Isn't Proof of Stake better?
PoS uses no energy but bases security on capital rather than physical energy. Pros and cons are philosophical and technical. Bitcoin's PoW community sees energy as feature (external cost = external trust), not bug.
Related terms
Further reading
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