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34 lines
2.6 KiB
Markdown
# Block
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A block is a collection of transactions that have been committed to the blockchain as a bundle.
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The transactions do not necessarily have to be related to one another and, generally, are only associated by virtue of when they were submitted to the Bitcoin Cash network.
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Every block contains one coinbase transaction, followed by zero or more additional transactions.
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The coinbase transaction is created by the miner of the block and provides an opportunity for them to receive the block reward for successfully mining a block, along with any fees collected from the transactions in the block.
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For more information, see [Mining](/protocol/mining).
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## Block Headers
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Block are identified by the SHA-256 hash of their header.
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Since the block header contains the root of a [Merkle Tree](/protocol/blockchain/merkle-tree) of the transactions in the block, this means the hash is ultimately dependent on both the meta-information about the block as well as the full contents of all of its component transactions.
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For more information see [Block Header](/protocol/blockchain/block/block-header).
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## Coinbase Transaction
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The coinbase transaction provides a mechanism for miners to:
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- Receive payment for mining.
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- Include a message, known as the "coinbase message," or simply "coinbase," within the block.
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To accomplish this, the coinbase transaction is required to have a single input.
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However, unlike other transactions, this input is not expected to provide the satoshis that appear in the outputs.
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Instead, the satoshis that appear in the outputs of the coinbase transaction are collected from two places: the block reward and transactions fees.
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The block reward is provided automatically to the block and represents a continually decreasing incentive for miners.
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The block reward started at 5,000,000,000 satoshis (50 BCH) and decreases by half every 210,000 blocks.
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Transaction fees are often required by the network for transactions to be relayed across the network.
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Satoshis provided as inputs to a transaction, but not consumed by its outputs, are collected by the coinbase transaction as implicit inputs.
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The coinbase message is provided in the inputs unlocking script. The unlocking script is required to begin with a push of the block height which can then be followed why whatever data is desired. The block height encoded as a variable-length, little-endian integer. The [OP_DATA_X](/protocol/blockchain/script/op-codes/op-data-x) operation is used to push the necessary number of bytes to encode the length. This requirement was added with version 2 blocks as a part of [BIP-34](/protocol/forks/bip-0034). |