A hard fork is a radical change to the protocol of a blockchain network that makes previously invalid blocks/transactions valid (or vice-versa). This requires all nodes or users to upgrade to the new rules in order to remain compatible with the network.
Put simply, a hard fork is a permanent divergence from the previous version of the blockchain, and nodes running previous versions will no longer be accepted by the newest version. A hard fork essentially creates a new blockchain, meaning that there is now an old and a new version of the Ethereum blockchain.
The most recent hard fork for Ethereum was Constantinople, which occurred on block 7,080,000 and implemented five EIPs (Ethereum Improvement Proposals). The primary purpose of this hard fork was to reduce the cost of gas for certain operations on the Ethereum network, as well as to delay the so-called “difficulty bomb” that would have made mining Ethereum more difficult (and thus less profitable) over time.
Constantinople also included changes that would make it easier for private blockchains (built on Ethereum) to interoperate with public Ethereum.
The Constantinople hard fork was originally planned for November 2018 but was delayed due to security concerns around one of the EIPs. It eventually went live on February 28, 2019.
Ethereum has had several other hard forks in the past, including Metropolis (which introduced Byzantium and Constantinople), Homestead (which made several changes to improve performance and security), DAO (which refunded investors who lost money in The DAO hack), and Spurious Dragon (which reversed transactions from The DAO hack).
What Is Hard Fork Ethereum?
A hard fork is a change to the protocol of a blockchain network that makes previously invalid blocks/transactions valid (or vice-versa). A hard fork essentially creates a new blockchain, meaning that there is now an old and a new version of the cryptocurrency.