In the UTXO model, a wallet's balance is not stored as a single number the way a bank account balance is. Instead, it is the sum of all the discrete unspent outputs from previous transactions that belong to that wallet's addresses. When a new transaction is sent, it consumes one or more existing UTXOs as inputs and creates new outputs, one going to the recipient and often another sent back to the sender as change, similar in principle to paying with a banknote and receiving change back rather than adjusting a single running total.
This differs from the account-based model used by networks such as Ethereum, where balances are tracked more like a running ledger tied to each address, updated directly with every transaction. The UTXO model has some advantages for privacy and for validating transactions in parallel, since unrelated UTXOs can be verified independently of one another, but it can make certain kinds of smart contract logic more complex to implement compared with a straightforward account balance that simply increases or decreases.
Wallet software generally handles the selection and combination of UTXOs automatically, so most users never need to think about the model directly, even though it underlies how their balance is actually represented and tracked on the network.
Puntos clave
- UTXO stands for Unspent Transaction Output, the unit that Bitcoin and similar blockchains use to track ownership.
- A wallet's balance is the sum of its unspent outputs rather than a single stored number, and transactions consume and create new outputs.
- The UTXO model differs from the account-based model used by networks like Ethereum, with different trade-offs for privacy and contract complexity.
UTXO — frequently asked questions
Why does Bitcoin use UTXOs instead of account balances?
The UTXO model was part of Bitcoin's original design and offers benefits such as easier parallel verification of unrelated transactions and a clear, auditable transaction history, though it involves different trade-offs than an account-based system.
Do I need to understand UTXOs to use a Bitcoin wallet?
Not for everyday use, since wallet software handles UTXO selection automatically in the background. It becomes more relevant for advanced users interested in transaction fees, privacy practices, or building applications directly on Bitcoin.
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