hard fork, soft fork

1 [concept]
The process of a blockchain being split into 2 blockchains
2 [concept]
A blockchain's validity is determined by the miners based on which chain is the longest. Sometimes, when groups of miners disagree on the cyptocurrencies protocol, the hashpower will split, and with that splitting the single blockchain into 2 separate blockchains. This is known as a fork. Usually one of the chains gains majority and the other chain dies off, but sometimes both chains maintain enough hash-power and support to co-exist and evolve independently
3 [hard fork]
A hard fork occurs when the consensus rules change in a way incompatible with previous versions. This splits the chain into two, and one of three things can happen. 1. Miners support the new chain, and the old version dies off. 2. Miners support the old version and the new version dies off. 3. Both versions gain enough support to live on independent from one another

3.1 Example | BCH <-> BTC

On August 1st, 2017, the original bitcoin chain split into 2 separate blockchains. Bitcoin (BTC), and Bitcoin Cash (BCH). Since this change introduced incompatibles, miners had to choose which fork to support. Each gained enough support to continue, and live on as independent project with their own communities, developers, and miners.

After the fork, for every bitcoin on the pre-fork blockchain, there now existed 1 Bitcoin Cash (BCH) and 1 Bitcoin (BTC)

3.2 Example | BTC <-> BTG

Bitcoin Gold (BTG) was another fork of the bitcoin chain, but it failed to gain enough community and miner support to make an impact, and soon became irrelevant

3.3 Example | BCH schedule

Bitcoin Cash (BCH) undergoes regularly planned hard-forks to update the network, currently scheduled every 6 months.

4 [soft fork]
A soft fork occurs when the consensus rules change in a way which maintains compatibility with the current consensus rules. Often times this requires new software to use the new features, but the network as a whole is able to continue without any disruption or updates.