Smith & Atlas 2016. (†830)Smith, Peter & Kristov Atlas. "A Brief History of Bitcoin Forks. (blockchain blog, 26 February 2016).
- hard fork (s.v. "introduction" ): A hard consensus fork occurs when blocks that would have previously been considered invalid are now valid. Any Bitcoin user, miner, exchanger, etc. who wants to stay in consensus with the network must upgrade his software during a hard consensus fork; otherwise, some new block that the network accepts will appear as invalid to him. (†2165)
- soft fork (s.v. "introduction"): A soft consensus fork occurs when blocks that would have previously been considered valid are now invalid. Upgrading software during a consensus soft fork is forever optional to a Bitcoin user, miner or exchanger, with the following caveats: · If the soft fork introduces a new feature that you want to use as either the sender or recipient, you must upgrade in order to use it. · At least 51% of miners must upgrade to adopt the soft fork; otherwise, it will forever appear as the shortest chain and get orphaned by the network. · Refusal to accept the soft fork can reduce your security. As you would normally consider soft forked transactions invalid, Bitcoin developers use various tricks to make these transactions appear valid to you while reducing your client’s capacity to process exactly why they are valid. See “Risks of Intentional Soft Consensus Forks” below. (†2166)