A type of protocol change that validates all previously invalid transactions, and invalidates all previously valid transactions.
The hard forking breaks the forward compatibility of crypto-assets. Therefore, even if the transaction history and parameters are the same before the hard fork, the history of both networks dissociates from one another after the event and any further activity beyond the fork will not reflect on the other. Hard forks can result accidentally from bugs/errors in the blockchain or be done intentionally (due to disagreements in the cryptocurrency community).
Hard forks are major events and are primarily broadcasted to a cryptocurrency’s community well in advance. They are the subject of major discussions and debates in the crypto community, as the community tries to find out the merit and drawbacks of modifying a particular characteristic of a project (mostly the block size, rewards and hard cap, etc.)
For instance, the proposal to hard fork Bitcoin in 2017 in order to increase its block size from 1 MB to 8 MB for faster and more transactions was met by strict opposition from the majority of the community.
As a result, a part of the community split and formed Bitcoin Cash (BCH). The cryptocurrency has had its own hard forks since, one that yielded Bitcoin Cash ABC (BTCA) and Bitcoin SV (BSV), and the latest 2020 fork that resulted in a new chain called Bitcoin Cash Node (BCHN) taking over the mantle from BTCA as the “official” BCH.
Ethereum, meanwhile, had a well-documented hardfork in 2016 following the DAO’s replay exploit which left the original chain to operate as Ethereum Classic. In 2020, Ethereum suffered an unexpected, but minor, hard fork after their developers didn’t properly relay unscheduled upgrades to their community and infrastructure providers, causing the likes of infrastructure provider Infura to run outdated and conflicting software.