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Concept
Architecture
The UTXO Model
First appeared Jan 2009
Why it matters
The UTXO model makes transactions independently verifiable and parallelizable, and underlies how Bitcoin proves ownership without any global account state.
What it is
Bitcoin tracks money not as account balances but as a set of Unspent Transaction Outputs — discrete chunks of coin that are consumed and recreated by each transaction, like handing over exact bills and getting change.