What is Hard Fork?
Hard fork is a terminology used in blockchain technology. It means a certain change in the network protocol that ultimately divides the entire blockchain into two separate blockchains that have the same origin. This can allow the network to diverge that makes the valid blocks and invalid transactions or vice versa. When both the blocks get the same weightage. The new ones follow the previous protocol and the other one follows the new protocol.
Over the past, hard fork has been a danger to both the major blockchain networks i.e. Btc and Eth. People do. Ethereum recently went under the London Hard Fork upgrade (the name comes from the city in which the annual Devcon conference is held.
Bitcoin has also gone through hard fork updates and resulted in Bitcoin SV, Bitcoin Cash etc.
How does Hard Fork work
Blockchain ultimately works in the same way. Miners have to verify the transactions based on a set of specific rules that they know.
These miners know about the rules and when new rules are to be involved that decides the validation of the block, the Fork is used. Some miners continue to use the old set of rules and some use the new set of rules.
What causes a Hard Fork?
There can be different reasons why the developers may choose implement Hard Fork updates. Some developers choose to implement a hard fork because they find security issues in the previous protocol.
Some may choose to implement it to reverse transactions. For example, the implementation of London Hard Fork update was to reverse the transactions caused by the hack on a DAO (Decentralized Autonomous Organization). The Ethereum community voted and allowed to implement and roll back the transactions that caused millions of dollar damage to users when an unknown person attacked removed the money.