How blockchains work

Blocks in a chain

A blockchain groups transactions into blocks. Each block includes a hash, a short fingerprint, of the block before it. Change one old transaction and its block's fingerprint changes, which breaks every link after it. That makes history very hard to rewrite quietly.

Bitcoin adds a block about every ten minutes, Ethereum every 12 seconds and Solana roughly every 400 milliseconds.

Who adds the next block?

Thousands of independent computers, called nodes, keep a copy of the chain. They need a fair way to agree on the next block. That rule is called consensus.

In proof of work, used by Bitcoin and Dogecoin, miners compete to solve a costly puzzle, and the winner adds the block and earns new coins. In proof of stake, used by Ethereum since the Merge in 2022 and by Solana, validators lock up coins as collateral and are picked to propose blocks. Misbehaving validators can lose part of their stake.

The XRP Ledger uses a third approach: validators vote over a few rounds until they agree, with no mining or staking reward.

Forks and upgrades

Rules change through software upgrades. A soft fork tightens the rules so old nodes still accept new blocks, like SegWit in 2017. A hard fork changes rules in a way old nodes reject. If part of the community refuses, the chain can split, as with Bitcoin Cash and Ethereum Classic. See our hard fork guide.