Modular blockchain

The four functions that get decoupled are execution (processing transactions and updating state), consensus (agreeing on transaction order), data availability or DA (guaranteeing that a block's data is published and retrievable) and settlement (the layer for finality and dispute resolution where rollups anchor their proofs). In the monolithic model, exemplified by Solana, a single chain does all four. In the modular model, a rollup typically handles execution and delegates consensus and DA to another layer.

The canonical case of a dedicated DA layer is Celestia, the first modular data availability network, with mainnet beta on 31 October 2023. It only handles consensus and data availability, leaving execution and settlement to other chains. Its key technique is Data Availability Sampling (DAS), which lets light nodes verify that a block's data is available without downloading the whole block, sampling random fragments backed by erasure coding. An alternative is EigenDA, which disperses data across its operators and publishes a proof on Ethereum.

The modular thesis tackles the scalability trilemma: instead of scaling a single chain, each function scales separately. The rollup bottleneck was the cost of publishing data on L1. Ethereum, though monolithic, partly modularized with EIP-4844 (proto-danksharding, blobs) in the Dencun hard fork of March 2024, and expanded that capacity with EIP-7691 in Pectra (mainnet on 7 May 2025), which raised the per-block blob target from 3 to 6 and the maximum from 6 to 9. For RWA issuers, a modular appchain or rollup enables dedicated, compliant environments (ERC-3643, KYC, MiCA) without building a full L1. The four layers are a conceptual framework, not a fixed and universal split.