Forking

A fork is said to have happened when there is a conflict among the nodes regarding the validity of a blockchain, that is, more than one blockchain happens to be in the network, and every blockchain is validated for some miners. There are three kinds of forks: regular forks, soft fork, and hard fork.

A regular fork is a temporary conflict occurring due to two or more miners finding a block at nearly the same time. It's resolved when one of them has more difficulty than the other.

A change to the source code could cause conflicts. Depending on the type of conflict, it may require miners with more than 50% of hash power to upgrade or all miners to upgrade to resolve the conflict. When it requires miners with more than 50% of hash power to upgrade to resolve the conflict, its called a soft fork, whereas when it requires all the miners to upgrade to resolve the conflict, its called a hard fork. An example of a soft fork would be if update to the source code invalidates subset of old blocks/transactions, then it can be resolved when miners more than 50% of hash power have upgraded so that the new blockchain will have more difficulty and finally get accepted by the whole network. An example of a hard fork would be an if update in the source code was to change the rewards for miners, then all the miners needs to upgrade to resolve the conflict.

Ethereum has gone through various hard and soft forks since its release.