This is the first of the two-part article on forks. Here we give a short overview of bitcoin forks in chronological order
A fork is a divergence in a blockchain which splits it in two chains. Major changes in protocols are introduced by way of hard forks, while minor improvements are implemented in soft forks.
Bitcoin XT is one of the earliest bitcoin forks initiated by Mike Hearn in December 2014. Originally, Bitcoin XT implemented new features suggested by Hearn in BIP64. Bitcoin XT gained notoriety in 2015 with the proposal of gradually raising the block size limit from 1MB to 8MB, outlined in Gavin Andresen’s BIP101. This change was not received warmly by the community. Today, Bitcoin XT is practically dead.
Bitcoin Classic was another attempt to address bitcoin scalability issues by raising block size limit. Bitcoin Classic was launched in 2016 proposing a 2MB blocks. While the project did gain some traction, it never really achieved a critical user base and got abandoned.
Bitcoin Unlimited is a bitcoin hard fork which lets miners customize the block size limit, which is 16MB by default. Initially, Bitcoin Unlimited showed ambitions capturing a relatively wide audience. However, the fork lost most of its popularity due to certain bugs that disrupted the network operation.
Segregated Witness (SegWit) is a bitcoin soft fork which increases block capacity by reducing the size of the transaction. SegWit was proposed by Bitcoin Core developer Peter Wuille in 2015. SegWit stores transaction signatures in another structure called an extended block, which frees up space for transactions in the mainchain block. Other advantages to SegWit include a fix to transaction malleability, which in turn enables second-layer solutions such as Lightning Network and atomic swaps.
Bitcoin Cash is a bitcoin hard fork activated in August 2017. The block size limit is Bitcoin Cash is 8MB. Bitcoin Cash quickly gathered support from major influencers, such as Roger Ver and ViaBTC. Bitcoin Cash does not support SegWit. Though Bitcoin Cash is now losing popularity due to exceeding controversy surrounding it, it is still one of the most widely adopted forks.
Bitcoin Gold is a bitcoin hard fork activated in October 2017. Bitcoin Gold aims to restore the mining functionality with common graphics cards, in place of mining with specialized ASICs, used to mine Bitcoin. Due to multiple attacks successfully executed on the network, Bitcoin Gold is not seeing popularity among crypto-enthusiasts.
SegWit2x was outlined in the New York Agreement signed by prominent figures in the space. SegWit2x proposed the activation of SegWit and a 2MB block size limit. The community naturally did not approve of the shady reunion, and the project failed.