What is a Rollup Rollup is a technology that scales Ethereum by "rolling" a large amount of computation and data from the main chain and putting it off-chain, and only submitting critical data to the chain, thereby increasing speed and reducing fees. ➣ Optimistic Rollup ▰ "optimistically" that off-chain transactions are correct ▰ Set a challenge period for each committed block (usually 7 days) ▰ During this period, anyone can submit a "fraud proof" to challenge the wrong transaction Advantages: Simple calculation and easy implementation Cons: Long waiting time for withdrawals (due to challenging periods) Representative projects: Arbitrum, Optimism ➣ ZK Rollup ▰ Generate a zero-knowledge proof when packaging a transaction to prove that the transaction is correct ▰ There is no need for a challenge period, the main chain verifies this proof to confirm that the transaction is valid Pros: Secure, fast withdrawals Disadvantages: ZK proof is computationally complex and expensive to develop Representative projects: zkSync, Starknet, and Scroll ➣ Hybrid Rollup ▰ Combine the advantages of both Optimistic and ZK ▰ The design may be fast executed by the optimistic mechanism first, and then asynchronous verification through ZK proof, or the two verification methods can be switched The goal: to balance performance, security, and development flexibility Representative projects: Fuel V2, Taiko (hybrid verification to be adopted)