State Machine

A blockchain behaves as a state machine: it holds one current state — every account balance, contract storage slot and nonce — and transactions are the inputs that move it from one valid state to the next. The rules for applying a transaction are deterministic, so any node replaying the same blocks from genesis must arrive at exactly the same state, which is what lets thousands of independent machines agree without a coordinator. This framing explains much of how the system feels in practice: transactions are ordered before they are executed, an invalid input is rejected outright rather than partially applied, and a rollup can prove it processed transactions correctly by proving that its state transition followed the rules.