What is a rollup?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
A rollup is a Layer 2 design that executes many transactions off-chain and posts a compressed record of the results to the main chain. How it proves those results are correct splits rollups into optimistic and zero-knowledge types.
Key points
- Batches execution off-chain and posts results to L1
- Data stays on L1, so the state can be reconstructed
- Two families, split by how correctness is proven
- Cuts the cost per transaction substantially
Definition
A Layer 2 approach that executes transactions off the main chain and records the outcome, plus the data needed to reconstruct it, on-chain in compressed form.
The defining property is that execution happens off-chain while the data stays on-chain. Because the data remains, anyone can rebuild current balances from the main chain even if the rollup's operators vanish — which is what separates a rollup from merely running a server.
How they prove the results differ. Optimistic rollups assume correctness and let anyone challenge with a fraud proof; zero-knowledge rollups attach a validity proof to every batch. The two differ in withdrawal delay and in computational cost.
A 2024 Ethereum upgrade introduced a data space dedicated to rollups, lowering what they pay to post to the main chain. Rollup fees therefore also move with changes to the base chain's own specification.
Watch out for
- · Rollups differ in how decentralised they are and who can pause them
- · Withdrawal times vary widely between designs