To understand what a Rollup is, you need to first understand Layer 1 and why blockchains hit speed and cost limits at scale.
Layer 1
Layer 1 is the base blockchain network — the foundational protocol layer. It handles everything from processing transactions to managing network security and consensus. Well-known Layer 1 blockchains include Ethereum, Bitcoin, Solana, Avalanche, and Cardano.
Layer 1 is responsible for validating and confirming transactions, storing data on-chain, running smart contracts, and maintaining network consensus. But it's also where limitations appear — slow speeds and high fees when demand spikes.
Layer 2 / Rollup
A Rollup is a type of Layer 2 scaling solution for blockchains, especially Ethereum. It helps the blockchain process more transactions faster and cheaper, while still relying on the security of the main chain.
Think of it this way: if Layer 1 is a busy highway, a Rollup is like a high-speed bus that picks up lots of passengers (transactions), drives on a faster side road, and only merges back into the highway occasionally to drop off a summary of its trip.
Benefits
Instead of every transaction being verified on Layer 1, a bunch of them are processed off-chain, then compressed and posted to Layer 1 in a single efficient batch. This gives: lower gas fees, faster transactions, and the same security as Layer 1.
Two main types
- Optimistic Rollups: Assume transactions are valid by default with a challenge period. Examples: Optimism, Arbitrum.
- ZK (Zero-Knowledge) Rollups: Use cryptographic proofs to prove transactions are valid. No challenge period needed. Examples: zkSync, StarkNet, Scroll.