Proof of History (PoH)
Solana's innovation of cryptographically timestamping events to order transactions before consensus — enabling high speed.
Proof of History, introduced by Solana, creates a verifiable, cryptographic record of time passing — a continuous hash chain that proves events occurred in a specific order. By establishing ordering before consensus, validators don’t have to communicate as much to agree on transaction sequence, enabling Solana’s very high throughput.
It’s not a standalone consensus mechanism but a complement to Proof of Stake, effectively a decentralized clock. The design choice reflects Solana’s bet on a single, ultra-fast chain rather than the rollup-based scaling Ethereum chose. Critics point to the higher hardware requirements this speed demands (fewer people can run nodes) as a decentralization trade-off — the recurring theme of the blockchain trilemma.