What is the difference between optimistic and ZK rollups?

Blockchain rollups are protocols that are designed to increase throughput and reduce fees. There are two types of rollups: optimistic and ZK (zero knowledge) rollups. Optimistic rollups are protocols that increase blockchain performance by grouping multiple transactions into a group. The group is processed offline, and compressed data is sent to the network. Optimistic protocols can increase the scalability of the blockchain by 10-100 times. In zero-knowledge rollups, groups of transactions are controlled by operators who prove the correctness of the changes by checking for fraud. It takes much less time and money to verify evidence than to control transaction data.