Zero-knowledge rollups (ZK-rollups) bundle (or "roll-up") hundreds of transfers off-chain and generate a cryptographic proof. Like Ethereum, a rollup protocol has a “virtual machine” that executes smart contract code. The rollup’s virtual machine operates independently from Ethereum’s own virtual machine (the EVM) but it is managed by an Ethereum smart contract.
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This connection allows rollups and Ethereum to communicate. A rollup executes transactions and processes data, and Ethereum receives and stores the results.