# Hard Fork Combinator Hard forks tend to be 'traumatic' events where a blockchain splits ('forks'), rendering the 'old' blockchain invalid, along with its transaction history, protocol, etc. The hard fork combinator is an IOG engineered, open-source technology that, rather than discarding the old data, combines two protocols into a single protocol. We call this a sequential combination of the two protocols because it runs the first protocol for a while and at some point, it switches over to the second. The current Cardano chain combines blocks of the following development phases: Byron, Shelley, Allegra, Mary, and Alonzo. After future transitions, it will also combine Goguen, Basho, and Voltaire blocks - all as a single property. We have successfully used this technology for all the hard forks that Cardano has undergone (except for the first one, where Cardano switched from Ouroboros Classic to Ouroboros BFT.) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://cardano-wiki.gitbook.io/cardano/how-does-cardano-work/table-of-contents/hard-fork-combinator.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.