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The Blockchain is a data structure. The block is composed of block header and block body. As each block has a crpytographic hash of the previous block, a timestamp, and transaction data (generally represented as a merkle tree root hash), and a chain structure is formed.

The data structure of block as following:

4VersionBlock VersionuintBlock version, current is 0
32PrevHashPrevious HashUInt256The previous block's hash
32MerkleRootMerkle Tree RootUint256The merkle tree root of the block's transactions
4TimestampBlock TimestampuintThe time when this block is generated
4IndexBlock IndexuintBlock height, and the Genesis Block's index is 0
8ConsensusDataNonceulongIt's a random value
20NextConsensusNext Consensus AddressUInt160The script hash of consensus nodes' multi-signature contract in the next round
1--uint8It's fixed 1 and added before Witness on serialization
?WitnessWitnessWitnessThe executable verification scripts
?*?TransactionsTransaction ListTransaction[]The payload of the block


Block Header

The block header contains the basic information of a block and provides verification of a block. The first 10 attributes of the block constitute the header.

Block hash and index can be used to identify a block. The hash value is obtained by concatenating the first seven attributes of the block header and performing SHA256 operation twice. Normally, NEO has only one chain, and each block is confirmed by more than two-thirds of the consensus nodes, before added to the blockchain. Therefore, the height of each block is unique. Block height must be equal to the previous block height plus 1, and the Genesis Block height is 0.

Timestamp is the bock's time stamp, must be bigger than the previous one.The invternal between two blocks is about 15 seconds, and is set by the variable SecondsPerBlock in the configuration file protocol.json .

NextConsensus is the hash of mulit-signature contract, which needs the signatures of more than two-thirds of the consensus nodes as parameters. The example script is shown as below. Each block, with the NextConsensus field, locks the nodes participating in the next round of consensus activity. In the previous round of consensus activity, the Speaker calcualted the consensus nodes of the next round based on the voting at that time, generated the multi-signature contract, and assigned the hash value of the contract to the block's NextConsensus field.

Witness is the verification script of the block, it contains InvocationScript and VerificationScript . The InvocationScript provides the parameters for the VerificationScript to execute.


Block Body

The block body is a transaction list. In one round of consensus activity, the Speaker selects all the transactions in the memeory pool, sort and filter by plugin, package them into a new proposal block. For more details about consensus, please read "Consensus Mechanism" section.

The first transaction of each block must be MinerTransaction , which is used for distribution of transaction's network fees in the block. At present, there can be up to 500 transactions per block and 20 free transactions among them.

When a block persistent, it stores a hash list of the block's transaction, and the transaction data is stored separately for facilitate query.