Glossary
Proof of History (PoH)
Solana's pre-consensus clock: a verifiable delay function that orders events in time before validators vote on them.
PoH is not a consensus mechanism on its own — it is a cryptographic clock that proves time has passed between events. The leader runs a SHA-256 sequence whose output at each step is the input to the next, producing an unforgeable ordering.
Solana uses PoH so transactions are already timestamped and ordered by the time they reach the PoS voting layer. That lets the network skip many of the back-and-forth communication rounds traditional BFT consensus requires, which (along with parallel execution) is what underpins Solana's throughput.