Blockchain: The Core of Distributed Ledgers
Bitcoin operates fundamentally differently from traditional banking systems. Instead of relying on a centralized server to record each user's account balance, it tracks all value transfers in a decentralized manner through a distributed public ledger called "Blockchain." All confirmed transactions are permanently recorded in this shared ledger.
A blockchain is essentially a linked list structure where a series of blocks are connected by cryptographic hash pointers. Each new block contains the hash value of the previous block, forming an immutable, chronologically ordered record of transaction history. This design ensures data integrity and security; any tampering with historical transactions would invalidate the hash values of subsequent blocks, causing them to be identified and rejected by the network.
UTXO Model: Managing Bitcoin Ownership
Bitcoin uses the Unspent Transaction Output (UTXO) model to manage ownership and transaction history, rather than a traditional "account balance" model. In the UTXO model, your Bitcoin "balance" is not a single number, but rather the sum of all your spendable UTXOs generated from previous transactions.
- Nature of UTXO: Each UTXO represents an independent unit of value recorded on the blockchain that can only be spent once. When a Bitcoin transaction occurs, it consumes one or more existing UTXOs as inputs and generates new UTXOs as outputs.
- Transaction Composition: A Bitcoin transaction typically includes the sender's and receiver's wallet addresses, the amount of Bitcoin transferred, and the time the transaction occurred.
- Digital Signature: To prove the legitimacy of a transaction, when a user initiates a transaction, their wallet key generates a digital signature. This signature serves as mathematical proof that the transaction indeed originated from the wallet owner and ensures that the transaction content cannot be maliciously altered after being broadcast.
Block Structure: Container for Data Encapsulation
Each Bitcoin block consists of two main parts: the Block Header and the Block Body.
- Block Header: Contains critical metadata for maintaining the blockchain's structure and security, such as the version number, hash of the previous block, Merkle root hash, timestamp, difficulty target, and a nonce. This information forms the basis for miners' proof-of-work calculations.
- Merkle Tree: All transaction data contained in the block body is processed using a hash structure called a Merkle Tree. The hash values of all transactions are combined layer by layer upwards, ultimately generating a unique Merkle root hash. This root hash is stored in the block header and efficiently verifies the integrity and immutability of all transactions within the block.
- Block Body: Actually stores all transaction records included in that block.
Transaction Storage and Verification Process
Bitcoin transactions undergo a series of complex steps from initiation and verification to final storage on the blockchain:
- Broadcast and Verification: When you initiate a transaction and digitally sign it, the transaction data is broadcast to the Bitcoin network, which consists of thousands of computers (nodes) worldwide. Nodes in the network independently verify the validity of this transaction, including whether the digital signature is correct, whether the sender has enough UTXOs to spend (rather than a simple "account balance"), and whether the transaction information complies with network rules.
- Mempool: Valid transactions that pass verification are not immediately added to the chain but enter an area called the "mempool," waiting for miners to select and package them into new blocks.
- Mining: Miners compete to create new blocks by solving a computational puzzle (Proof of Work, PoW). They select transactions from the mempool, package them into a new block, and try to find a nonce that meets the difficulty target. Once found, the miner has successfully "mined" the new block. This process mandatorily ensures that data in the blockchain is stored chronologically and maintains the network's decentralization and neutrality.
- Confirmation: After a new block is added to the blockchain, other nodes in the network verify its validity. Once a block is accepted, the transactions it contains are considered "one confirmation." To ensure the finality and irreversibility of a transaction, it is generally recommended to wait for 6 confirmations (approximately 1 hour), meaning 6 new blocks have been generated after your transaction, making the possibility of it being rolled back extremely low.
- Full Nodes: Computers running the complete Bitcoin client program are called full nodes. They store and verify a complete copy of the blockchain, including all historical transactions and blocks, serving as the cornerstone for maintaining the security and decentralized nature of the Bitcoin network.
Bitcoin Blockchain Data Size
Bitcoin's block size was initially limited to 1MB. However, the Segregated Witness (SegWit) upgrade in 2017 theoretically allowed block size to expand to 4MB, though the actual average block size is usually around 2MB. Over time, with increasing transaction volume, the total data size of the Bitcoin blockchain continues to grow. As of October 6, 2026, a complete copy of the Bitcoin blockchain has reached approximately 773.59 GB. Users can view real-time Bitcoin market data and related data progress on market information platforms like Svmuu.
