// GLOSSARY -- WEB3 INFRASTRUCTURE

What is Rollup?

1 min read Updated

A rollup is a Layer 2 scaling solution that executes transactions off-chain, bundles them together, and posts compressed data or proofs to the Layer 1 blockchain — inheriting L1 security while dramatically increasing throughput.

WHY IT MATTERS

Rollups are Ethereum's scaling strategy. Instead of processing every transaction on L1 (expensive, slow), rollups batch hundreds of transactions off-chain and post only the essential data to Ethereum. This provides 10-100x cost reduction while inheriting Ethereum's security.

Two types: optimistic rollups (assume transactions are valid, allow a challenge period for fraud proofs) and ZK rollups (generate cryptographic proofs of validity upfront). Both post data to L1 for verification.

Major rollups include Arbitrum, Optimism, Base (optimistic) and zkSync, Starknet, Polygon zkEVM (ZK). The rollup ecosystem is where most Ethereum development is happening.

FREQUENTLY ASKED QUESTIONS

How do rollups inherit L1 security?
By posting transaction data/proofs to L1. Anyone can verify rollup state by replaying the posted data (optimistic) or checking the validity proof (ZK). L1 serves as the source of truth.
Optimistic vs ZK rollups?
Optimistic: simpler technology, EVM compatible, 7-day withdrawal delay. ZK: cryptographic security, faster withdrawals, but more complex technology and less EVM compatibility currently.
Are rollups decentralized?
Most rollups currently have centralized sequencers (single entity ordering transactions). Decentralizing sequencers is a major roadmap item for all rollup projects.

FURTHER READING

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