An account-based ledger tracks a changing balance by applying each valid transaction to shared current state, then committing the resulting account values to a new state root.

That is the crucial distinction from a UTXO ledger such as Bitcoin. A UTXO wallet spends particular outputs and creates new ones; an account model keeps an address and mutates its balance. Send 4 tokens from an address holding 10 to one holding 3, and the next state records 6 and 7. The chain still keeps the transaction and receipt, but those are evidence of the change, not the balance itself.

What Actually Changes

On an Ethereum-style network, a native-asset transfer updates the sender and recipient account balances and the sender’s nonce. A contract call can update much more. An ERC-20 token typically stores balances in the token contract’s mapping from address to integer; transfer logic subtracts from one entry, adds to another, and emits a Transfer event.

• Input: a signed transaction identifies the sender, nonce, gas limit, and call data.
• Execution: the EVM checks authorization and runs contract code, possibly calling other contracts.
• State write: contract storage and transfer effects change only if execution succeeds; a reverted call leaves no final execution change.
• Proof: the block commits to a state root, while receipts and logs let software reconstruct what happened.

The last two are often blurred. An event log is excellent for indexing transfers, but it is not an independent authority over the current balance: a reader can verify the token contract’s balanceOf value against chain state. That settles a recurring disagreement between “the ledger is the history” and “the ledger is the state.” For a current balance, state wins; history explains how it got there.

Why This Matters in DeFi

Because contracts can read and write shared state during one transaction, a router can move tokens, update a pool, and settle the user’s output atomically. That composability is the practical gain: no central operator has to reconcile separate databases before the next action. In Balancer Protocol, pool accounting and token custody are handled by contracts; with the Frax Dollar, the token contract’s balances are likewise distinct from the AMM’s pool balances.

The relevant point in a Frax Swap trade is not the interface’s number but the pool contract’s state. The pool contract’s balances are the values pricing code reads and changes; Frax Swap gives that account-and-contract pattern a concrete instance.

Before trusting a dashboard, identify the chain, token contract, and address it is querying. The model does not apply to an exchange’s private database, and a rebasing or share-based token may compute the displayed amount from stored shares and an index. In ordinary ERC-20 use, read contract state first and use logs as the audit trail.