Proof of Work (PoW)

Proof of work (PoW) is a consensus mechanism in which computers compete to solve a hard mathematical puzzle for the right to add the next block of transactions to a blockchain. Finding a solution takes an enormous number of guesses and therefore real electricity, while verifying a solution is instant for everyone else. The winner earns newly issued coins plus transaction fees, and rewriting past blocks would mean redoing all that work, which is what makes the chain expensive to attack. Bitcoin is the best-known proof-of-work network. The main criticisms are high energy consumption and the concentration of specialised mining hardware in a few large operations, which is one reason several projects use proof of stake instead.