21 BTCBlock
A block is a batch of Bitcoin transactions added to the chain about every ten minutes. The miner who finds it collects the new coins and the fees.
Short definition
A batch of transactions added to the chain about every 10 minutes.
What is inside
A block is a header plus a list of transactions. The first transaction is the coinbase: it has no inputs and pays the miner the block subsidy plus all fees. The others are ordinary payments picked from the Mempool, usually by highest fee rate.
Since SegWit (BIP 141) block size is measured in weight: at most 4,000,000 weight units, where non-witness bytes count four times and witness (signature) bytes once. In practice that allows blocks of up to about 4 MB, typically 1.5–2 MB.
Timing
Blocks arrive at random: ten minutes is only the average. The Difficulty adjustment every 2,016 blocks pulls the average back to ten minutes when miners join or leave.
See also
- BlockchainThe blockchain is Bitcoin's shared history of payments: a chain of blocks where each block points to the one before it. Changing an old block would break every link after it.
- MiningMining is the work that adds new blocks to Bitcoin. Miners run special computers (ASICs) that guess numbers; the winner of each round earns the block subsidy and the fees.
- MempoolThe mempool is the waiting room for Bitcoin payments: transactions sent but not yet in a block. Miners usually pick the ones paying the highest fee per byte first.
- HalvingEvery 210,000 blocks, roughly every four years, the number of new bitcoins paid to miners per block is cut in half. This is how Bitcoin's supply is capped at 21 million.
- SegWit (Segregated Witness)SegWit was a 2017 upgrade that moved signatures into a separate part of the transaction. It fixed a long-standing bug, made room for more transactions and opened the door to the Lightning Network.
- Genesis blockThe genesis block is block 0, the first block of Bitcoin, mined by Satoshi Nakamoto on 3 January 2009. It carries a newspaper headline about bank bailouts.
References
- BIP 141 (github.com/bitcoin/bips) github.com
- Bitcoin developer reference: block headers developer.bitcoin.org