Definition ∞ The longest chain rule is a consensus mechanism primarily used in Proof-of-Work blockchains, such as Bitcoin, to determine the authoritative version of the transaction history. When two or more valid blocks are mined simultaneously, creating a temporary fork, the network adopts the chain that accumulates the most subsequent blocks, thereby becoming the longest. This rule helps maintain network consistency.
Context ∞ News often refers to the longest chain rule when explaining blockchain forks, network security against 51% attacks, and the fundamental principles of Proof-of-Work consensus. Its operation is critical for preventing double-spending and ensuring the immutability of the ledger. Understanding this rule is essential for comprehending how decentralized networks resolve conflicting transaction histories.
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