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About hard forks

The term hard fork describes a radical change in the blockchain: a change from one protocol to another, for example. In most blockchains, a hard fork indicates block changes or a change to their interpretation.

Traditionally, when conducting a hard fork, the current protocol would stop operating, new rules and changes would be implemented, and the chain would restart. It is important to note that a hard-forked chain will be different from the previous version and that the history of the pre-forked blockchain will no longer be available.

The Cardano blockchain hard forked from a Byron federated model to a Shelley decentralized one in 2020. However, this hard fork was unique. Instead of implementing radical changes, Cardano ensured a smooth transition to a new protocol while saving the history of the previous blocks. This means that the chain did not change radically, instead, it contained Byron blocks, and after a transition period, added Shelley blocks. There was no fundamental restart point that erased the history of previous activities.

What is a hard fork combinator?

A combinator is a technical term used to indicate the combination of certain processes or things. In the case of Cardano, a hard fork combinator combines protocols, thereby enabling the era-to-era transition without system interruption or restart. It ensured that Byron and Shelley ledgers appeared as one ledger. Shifting from Ouroboros BFT to Ouroboros Praos did not require all nodes to update simultaneously. Instead, nodes could update gradually, in fact, some could run Byron blocks, while others could run Shelley blocks.

The hard fork combinator is designed to enable the combination of several protocols, without having to make significant adjustments.

Read more about Cardano's upgrades in the following section.