Crypto glossary
Hard fork
A hard fork is a change to a blockchain's rules that is not backward compatible, so nodes that do not upgrade split off from the network.
A hard fork changes the protocol in a way that older software considers invalid. Every node must upgrade to keep following the main chain; those that do not end up on a separate chain with the old rules. A soft fork, by contrast, tightens the rules so that nodes that have not upgraded still accept the new blocks.
Most hard forks are planned upgrades with broad support, such as Ethereum's regular network upgrades, and leave a single chain. When a community disagrees, however, both sides can keep running, creating two coins. Ethereum Classic came out of the 2016 dispute over The DAO hack, and Bitcoin Cash split from Bitcoin in 2017 over block size.
After a contentious split, holders typically own coins on both chains, and exchanges decide which ones to list and under which ticker.
Example
When Bitcoin Cash forked in August 2017, anyone holding 1 BTC at the split block also received 1 BCH on the new chain.
Related terms
Latest articles on Hard fork
- What is a Bitcoin Hard Fork?
- Polygon Proposes Network Hard Fork To Recover $6.8M In Stolen POL Tokens
- BNB Chain Sets October 28 Testnet Launch for Major Jenner Hard Fork Upgrade
- Binance Halts Base Network Transfers as Major Upgrade and Hard Fork Nears
- Core DAO Contains Incident And Prepares Hard Fork To Block Malicious Validators
