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List of bitcoin forks

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Bitcoin forks are defined variantly as changes in the protocol of the bitcoin network or as the situations that occur "when two or more blocks have the same block height".[1] A fork influences the validity of the rules. Forks are typically conducted in order to add new features to a blockchain, to reverse the effects of hacking or catastrophic bugs. Forks require consensus to be resolved or else a permanent split emerges.

Forks of the client software

The following are forks of the software client for the bitcoin network:

Bitcoin XT
A fork initiated by Mike Hearn. The current reference implementation for bitcoin contains a computational bottleneck.[2] The actual fork was preceded by Mike Hearn publishing a Bitcoin Improvement Proposal (BIP 64) on June 10, 2014, calling for the addition of "a small P2P protocol extension that performs UTXO lookups given a set of outpoints."[src 1] On December 27, 2014 Hearn released version 0.10 of the forked client XT, with the BIP 64 changes.[src 2] It achieved significant attention within the bitcoin community in mid-2015 amid a contentious debate among core developers over increasing the block size cap.[3]
On June 22, 2015, Gavin Andresen published BIP 101 calling for an increase in the maximum block size. The changes would activate a fork allowing eight MB blocks (doubling in size every two years) once 75% of a stretch of 1,000 mined blocks is achieved after the beginning of 2016.[src 3] The new maximum transaction rate under XT would have been 24 transactions per second.[4]
On August 6, 2015 Andresen's BIP101 proposal was merged into the XT codebase.[src 4][src 5] Bip 101 was reverted[src 6] and the 2-MB block size bump of Bitcoin Classic was applied instead.[citation needed]
The August 2015 release of XT received widespread media coverage. The Guardian wrote that "bitcoin is facing civil war".[3]
Wired wrote that "Bitcoin XT exposes the extremely social — extremely democratic — underpinnings of the open source idea, an approach that makes open source so much more powerful than technology controlled by any one person or organization."[5] Developer Adam Back was critical of the 75% activation threshold being too low and that some of the changes were insecure.[6]
On August 25, 2017, Bitcoin XT published Release G, which was a Bitcoin Cash client by default.[src 7] Subsequently, Release H was published, which supported the November 2017 Bitcoin Cash protocol upgrade, followed by Release I, which supported the May 2018 Bitcoin Cash protocol upgrade.[citation needed]
Bitcoin Classic
In its first 8 months, Bitcoin Classic promoted a single increase of the maximum block size from one megabyte to two megabytes.[7] In November 2016 this changed and the project moved to a solution that moved the limit out of the software rules into the hands of the miners and nodes.[8]
Bitcoin Unlimited

All three software clients attempt to increase transaction capacity of the network. None achieved a majority of the hash power.[9]

Intended hard forks splitting the cryptocurrency

Hard forks splitting bitcoin (aka "split coins") are created via changes of the blockchain rules and sharing a transaction history with bitcoin up to a certain time and date. The first hard fork splitting bitcoin happened on 1 August 2017, resulting in the creation of Bitcoin Cash.

The following is a list of notable hard forks splitting bitcoin by date and/or block:

  • Bitcoin Cash: Forked at block 478558, 1 August 2017, for each bitcoin (BTC), an owner got 1 Bitcoin Cash (BCH)
    • Bitcoin SV: Forked at block 556766, 15 November 2018, for each Bitcoin Cash (BCH), an owner got 1 Bitcoin SV (BSV).
  • Bitcoin Gold: Forked at block 491407, 24 October 2017, for each bitcoin (BTC), an owner got 1 Bitcoin Gold (BTG)

Intended soft forks splitting from a not-most-work block

  • The fork fixing the value overflow incident was controversial because it was announced after the exploit was mined. It was assigned CVE-2010-5139.

Intended soft forks splitting from the most-work block

Unintended hard forks

Two hard forks were created by "protocol change" definition:

  • March 2013 Chain Fork (migration from BerkeleyDB to LevelDB caused a chain split)[10]
  • CVE-2018-17144 (Bitcoin 0.15 allowed double spending certain inputs in the same block. Not exploited)


Source code

Other references

  1. ^ Antonopoulos, Andreas (2017). Mastering Bitcoin: Programming the Open Blockchain (2 ed.). USA: O' Reilly media, inc. p. Glossary. ISBN 978-1491954386.
  2. ^ Maria Bustillos (25 August 2015). "Inside the Fight Over Bitcoin's Future". The New Yorker. Conde Naste. Retrieved 7 January 2017.
  3. ^ a b Alex Hern (17 August 2015). "Bitcoin's forked: chief scientist launches alternative proposal for the currency". the Guardian. Retrieved 20 August 2015.
  4. ^ Tim Hornyak (21 August 2015). "Bitcoin XT debate overshadowing growth opportunities". PC World. IDG. Retrieved 7 January 2017.
  5. ^ Cade Metz (19 August 2015). "The Bitcoin Schism Shows the Genius of Open Source". WIRED.
  6. ^ Everett Rosenfeld (20 August 2015). "Bitcoin splits: Will it break, or be better than ever?". CNBC. Retrieved 5 January 2017.
  7. ^ Paul Vigna (17 January 2016). "Is Bitcoin Breaking Up?". WSJ.
  8. ^ "Classic is Back". Archived from the original on 2017-02-02. Retrieved April 28, 2017.
  9. ^ Ammous, Saifedean (2018). The Bitcoin Standard: The Decentralized Alternative to Central Banking. John Wiley & Sons. pp. 227, 228. ISBN 9781119473893. Retrieved 23 April 2018.
  10. ^ March 2013 Chain Fork