How rollups let a blockchain do 100× more without getting bigger

A blockchain like Ethereum is slow on purpose: every one of thousands of nodes must re-execute every transaction to agree on the result. That's what makes it trustworthy — and what caps it at a handful of transactions per second. Rollups are the leading fix, and the trick is deceptively simple: do the work somewhere else, then post just the proof back.

A rollup runs its own chain that processes hundreds of transactions off to the side. Instead of asking Ethereum to re-run all of them, it batches them together, compresses the data, and posts a summary to the main chain (the Layer 1). Ethereum stores that data and settles the final balances, so the rollup inherits L1's security without inheriting its congestion. The heavy computation happens on Layer 2; only the compact result touches L1.

The catch is convincing everyone the off-chain work was honest. Two designs answer this differently. Optimistic rollups assume batches are valid and open a challenge window (often ~7 days) during which anyone can submit a fraud proof to reverse a lie. ZK rollups instead attach a cryptographic validity proof to every batch, mathematically guaranteeing correctness up front — more complex to build, but no waiting period.