Proof
of History

Order of service

1. I

   The Life

   Proof of History was a clock you could check. The block producer ran SHA-256 over and over, each hash fed into the next, and counted. You can't skip ahead in a chain like that, so the count itself proved time had passed. Transactions were mixed into the chain as it ran, which stamped each one with a place in line.

2. II

   The Work

   Anyone could verify the chain later, and quickly, by checking pieces of it in parallel. So validators could agree on the order and timing of events without first talking to each other about it. It was Solana's founding idea, set out by Anatoly Yakovenko in a whitepaper in late 2017.

3. III

   The Passing

   Under Tower BFT, validators voted on blocks with on-chain transactions, and each vote locked them in for longer, timed by the clock. Finality took about 32 rounds of that, roughly 12.8 seconds.

   Alpenglow votes differently. Validators send votes straight to each other, off-chain, and a block is final after one round if 80% agree, or two rounds at 60%. Each validator runs a timer for how long a slot should take: if the block shows up in time, approve it; if not, skip it. With voting that fast, the network no longer needs a verifiable clock to keep everyone in step.

4. IV

   Survived By

   Votor, which handles voting and finality, combining thousands of votes into one small certificate, and Rotor, which carries blocks between validators. Finality now lands in about 100 to 150 milliseconds.

   Laid to rest beside it, the same afternoon: Tower BFT, and the on-chain vote transaction, which in its last block was 649 of 1,051 transactions.

   In lieu of flowers, please leave flowers.