Hard Fork

A hard fork is a change to a blockchain's rules that older software does not recognise, so participants must upgrade to stay on the new chain. Blocks that are valid under the new rules are rejected by non-upgraded nodes, and if a meaningful part of the community refuses to upgrade, the network can split permanently into two chains that share a common history — Bitcoin Cash separating from Bitcoin is a well-known example. Hard forks are used to add features, repair serious flaws or reverse contested events, and they need broad coordination among developers, miners or validators, exchanges and wallet providers. After a split, holders of the original coin normally hold balances on both chains, and each trades separately.