What Is a Hard Fork Combinator?

A hard fork combinator (first designed by IOHK) is a tool to combine protocols specifically on the Cardano blockchain after a hard fork has occurred.

How Does a Hard Fork Occur?

A hard fork normally occurs to implement upgrades to the blockchain. It requires multi-partner signatures and normally modifies certain parameters of the existing protocol. 

The hard fork is a split of a blockchain into two different protocols that run parallel to each other, where the new blockchain loses track and history of the previous one. 

Generally, hard forks cause some downtime on the blockchain, which disrupts the transactions and user experience. Another way is to implement a hard fork on the live blockchain, which may result in compromising blockchain integrity. For example, the Bitcoin hard fork in 2017 resulted in the splitting of the chain and the formation of Bitcoin Cash (BCH). This eventually affected the investor and trader interests. 

However, IOHK came up with the support of a hard fork combinator, which solves both of these problems efficiently.

What Is a Hard Fork Combinator (HFC)? 

A hard fork combinator is mainly used to merge pre and post-upgrade protocols after a hard fork so that the possibility of interruptions or restarts is removed.

When a hard fork takes place, it is virtually impossible for all the nodes to update to the new parameters and block headers at the same time without interruptions. Therefore, it becomes necessary to take the blockchain into downtime, which is disturbing for users. 

As a solution to this dilemma, IOHK Foundation came up with the hard fork combinator (HFC) for the Cardano (ADA) blockchain that allows multiple protocols to appear as one ledger so all the nodes don’t have to update to the new blockchain at the same time.

Cardano upgraded from Byron (wallet-only protocols) to Shelley (proof-of-stake supported protocols) in July 2020 where the hard fork modified the features and overall utility of the blockchain. Having a total of more than 1 million wallets at that time, a poorly executed hard fork would have meant the death of Cardano and its funds. 

However, the hard fork combinator was put to use for the first time, and on July 29, 2020, at 21:45 UTC, the transition from Byron to Shelley took place smoothly without any downtime or blunders. The users were informed but not restricted for usage and the hard fork took place in the background allowing the gradual transition of nodes with the passage of time. 

The Cardano blockchain, to this date, combines Byron and Shelley blocks. In further upgrades too, the transitions will be supported by the hard fork combinator.