In a blockchain, data is stored in a series of blocks that are linked together in a chronological and immutable chain. Each block contains a set of transactions or data records, along with a header that includes metadata such as a timestamp, a reference to the previous block’s hash, and a unique identifier known as a block hash.

Here’s how data is exactly stored in a blockchain:

1. Transaction Creation: When a user initiates a transaction on a blockchain network, whether it’s sending cryptocurrency, executing a smart contract, or recording data, the transaction is created and broadcasted to the network.
2. Validation and Confirmation: The transaction is then validated and confirmed by network participants, also known as nodes, using a consensus mechanism such as proof-of-work (PoW) or proof-of-stake (PoS). Once validated, the transaction is added to a pool of unconfirmed transactions known as the mempool.
3. Block Formation: Miners or validators on the network compete to create a new block containing a set of confirmed transactions. Miners bundle transactions together into a block and compete to solve a complex cryptographic puzzle to find a valid block hash.
4. Block Validation: Once a miner finds a valid block hash, they broadcast the new block to the network for validation. Other nodes on the network verify the transactions within the block, ensuring they meet the network’s consensus rules and are valid.
5. Linking Blocks: Each new block contains a reference to the hash of the previous block in the chain, forming a continuous and linear sequence of blocks. This linking of blocks ensures the integrity and immutability of the blockchain, as altering the data in one block would require changing all subsequent blocks in the chain.
6. Consensus: Consensus mechanisms ensure that all nodes on the network agree on the state of the blockchain and the validity of transactions. This prevents double-spending, ensures data integrity, and maintains the security of the network.
7. Data Storage: The actual data stored in a blockchain can vary depending on the type of blockchain and its use case. In a cryptocurrency blockchain like Bitcoin, data primarily consists of transaction details such as sender, receiver, amount, and transaction ID. In other blockchains, data can include smart contract code, digital assets, identity information, or any other type of digital record.
8. Distribution and Replication: Once a block is added to the blockchain, it is distributed and replicated across all nodes in the network. This distributed ledger ensures that each node has a copy of the entire transaction history, providing redundancy and resilience against data loss or tampering.

By following these steps, blockchain technology securely stores data in a decentralized, transparent, and immutable manner, providing trust and reliability in digital transactions and record-keeping.