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Collection 3 of 5 · 6 cards

Agreement (consensus)

Thousands of independent computers must agree on which block comes next, without a referee. These six cards explain the two main methods for reaching that agreement, the people and machines who take part, and what happens when the network briefly disagrees.

Cards in this collection

  1. What is a nonce?

    A nonce is a "number used once": in proof-of-work mining it is the header field that miners change again and again to get a new block hash, and on Ethereum it is also the counter that numbers each account's transactions.

    2 min read

  2. What is proof of work?

    Proof of work is a consensus method in which the right to add the next block goes to whoever first finds a block hash below a target — something that takes enormous computation to find but a single calculation to check.

    2 min read

  3. What is proof of stake?

    Proof of stake is a consensus method in which participants lock up the network's own units as a deposit, take turns proposing and voting on blocks, and can lose part of that deposit if they break the rules.

    2 min read

  4. What is a validator?

    A validator is a participant in a proof-of-stake network who has locked a deposit and, in exchange, may propose blocks and must vote on which blocks are correct.

    2 min read

  5. What is finality?

    Finality is the point after which a transaction recorded on a blockchain can no longer be reversed or replaced under the network's rules.

    2 min read

  6. What is a fork in blockchain?

    A fork is a split in a blockchain: either a short-lived branch when two valid blocks appear at once, or a change to the rules that some or all nodes adopt.

    2 min read