Bitcoin block(s) are data structures within the blockchain database, where transaction data in a cryptocurrency blockchain are permanently recorded. A block records some or all of the most recent transactions not yet validated by the network. Once the data are validated, the block is closed. Then, a new block is created for new transactions to be entered into and validated.
A block is thus a permanent store of records that, once written, cannot be altered or removed.
How a Bitcoin Block Works
A blockchain network witnesses a great deal of transaction activity. When used in cryptocurrency, maintaining a record of these transactions helps the system track how much was or wasn’t used and which parties were involved. The transactions made during a given period are recorded into a file called a block, which is the basis of the blockchain network.
A block stores information. Many pieces of information are included within a block, but it doesn’t occupy a large amount of storage space. Blocks generally have these elements, but they might vary between different types:
- Magic number: A number containing specific values that identify that block as part of a particular cryptocurrency’s network.
- Blocksize: Sets the size limit on the block so that only a specific amount of information can be written in it.
- Block header: Contains information about the block.
- Transaction counter: A number representing how many transactions are stored in the block.
- Transactions: A list of all of the transactions within a block.
The transaction element is the largest because it contains the most information. It is followed in storage size by the block header, which includes these sub-elements:
- Version: The cryptocurrency version being used.
- Previous block hash: Contains a hash (encrypted number) of the previous block’s header.
- Hash Merkle root: Hash of transactions in the Merkle tree of the current block.
- Time: A timestamp to place the block in the blockchain.
- Bits: The difficulty rating of the target hash, signifying the difficulty in solving the nonce.
- Nonce: The encrypted number that a miner must solve to verify the block and close it.
One 32-bit number in the header is called a nonce—the mining program uses random numbers to “guess” the nonce in the hash. When a nonce is verified, the hash is solved when the nonce, or a number less than it, is guessed. Then, the network closes that block, generates a new one with a header, and the process repeats.
Different mechanisms are used to reach a consensus; the most popular cryptocurrency is proof-of-work (PoW), with proof-of-stake (PoS) becoming more so because of the reduced energy consumption compared to PoW.