Hard forks
Hard forks are rare because they're considered risky: They
- take much coordination effort and
- are not backward compatible (it's a protocol upgrade)
After a hard fork, there will be two
blockchains: a majority and a minority chain. The implication is: some users will see a different set of
transactions than others.
Hard forks require all full
nodes to upgrade or everyone who uses that node may lose money.
Some forks
Allegedly, there are over 100 forks.
The most prominent forks include
| Bitcoin XT | BIP 64. Expands the block size to 8 MB |
| Bitcoin Classic | Increases the block size to 2 MB |
| Bitcoin Unlimited | |
| Segregated Witness (Segwit) | BIP 141, reduction of the Bitcoin transaction size by removing signatures from transactions which occupy up to 60 % of the blockchain. With Segwit, the signatures are stored on an extended block. Segwit also offers a solution to trasnaction malleability which was a bug in the blockchain. |
| Bitcoin Cash (Bcash) | Forked at block 478558 (2017-08-01). An owner of 1 BTC got one Bitcoin Cash (BCH). Bitcoin Satoshi Vision is a hard fork of Bitcoin Cash |
| Bitcoin Gold | Forked at block 491407 (2017-10-24). An owner of 1 BTC got one Bitcoin Gold (BTG) |