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Fork | Bitcoin Glossary | Mapping Bitcoin

Fork

Protocolo

Also known as: chain split

A divergence in the blockchain or protocol rules. Forks can be temporary (when two miners find blocks simultaneously) or permanent (when protocol rules change). Protocol forks are classified as either soft forks (backward-compatible) or hard forks (non-backward-compatible).

Overview

In Bitcoin, the term "fork" refers to any situation where the blockchain diverges into two or more potential paths. This can happen naturally during normal operation (temporary forks) or intentionally through protocol changes (soft forks and hard forks). Understanding the different types of forks is essential to grasping how Bitcoin evolves and maintains consensus.

Types of Forks

┌──────────────────────────────────────────────────────┐
│                    FORK TYPES                        │
├──────────────────┬───────────────────────────────────┤
│ Temporary Fork   │ Natural occurrence when two       │
│ (Stale Block)    │ miners find blocks at nearly the  │
│                  │ same time. Resolved automatically  │
│                  │ when the next block extends one    │
│                  │ chain, making it longer.           │
├──────────────────┼───────────────────────────────────┤
│ Soft Fork        │ Backward-compatible rule change.  │
│                  │ Old nodes still accept new blocks. │
│                  │ Tightens the consensus rules.      │
│                  │ Examples: SegWit, Taproot          │
├──────────────────┼───────────────────────────────────┤
│ Hard Fork        │ Non-backward-compatible change.   │
│                  │ Old nodes reject new blocks.       │
│                  │ Can cause permanent chain split.   │
│                  │ Example: Bitcoin Cash (2017)       │
└──────────────────┴───────────────────────────────────┘

Temporary Forks

     Block N        Block N+1a
... ─────────── ┬── ────────── ──► (Chain A, eventually wins)
                │
                └── ────────── ──► (Chain B, becomes stale)
                    Block N+1b

When Block N+2 is found extending Chain A,
Chain B's block becomes a stale block (orphan).

Temporary forks happen regularly and are resolved by Bitcoin's longest-chain rule: nodes always follow the chain with the most accumulated proof of work. Transactions in the losing block return to the mempool and are typically included in a subsequent block.

Notable Forks in Bitcoin History

  • 2010 value overflow: A bug allowed the creation of billions of bitcoin. Fixed with a soft fork that invalidated the offending block.
  • 2013 chain split: A database upgrade in Bitcoin 0.8 caused incompatibility with older versions, resulting in a temporary chain split that required coordinated action to resolve.
  • 2017 SegWit (soft fork): Activated via BIP141, adding witness data segregation and fixing transaction malleability.
  • 2017 Bitcoin Cash (hard fork): Increased the block size limit, creating a permanent chain split and new cryptocurrency.
  • 2021 Taproot (soft fork): Activated via Speedy Trial, adding Schnorr signatures and MAST scripting capabilities.

Fork Activation Mechanisms

Bitcoin has used several mechanisms to coordinate protocol upgrades:

  • Flag day: A predetermined block height at which new rules activate
  • Miner signaling (BIP9): Miners signal readiness by setting version bits; activation occurs when a threshold is reached
  • Speedy Trial: A faster variant of BIP9 with a shorter signaling period
  • User Activated Soft Fork (UASF): Nodes enforce new rules on a specific date regardless of miner signaling

Common Misconceptions

  • Not all forks create new cryptocurrencies. Only contentious hard forks where a significant portion of the community disagrees result in a permanent split.
  • Temporary forks are not a security concern. They are a normal part of distributed consensus and are resolved within minutes.
  • A soft fork does not require all users to upgrade, though upgrading provides access to new features and the strongest security guarantees.

Termos Relacionados

Soft ForkProtocolo

A backward-compatible change to Bitcoin's consensus rules that tightens existing rules (making some previously valid blocks/transactions invalid). Non-upgraded nodes still accept new blocks, though they may not fully validate the new rules. SegWit and Taproot were soft forks.

Hard ForkProtocolo

A backward-incompatible change to Bitcoin's consensus rules that makes previously invalid blocks or transactions valid. Hard forks require all nodes to upgrade and can cause a permanent chain split if not universally adopted.

ConsensusProtocolo

The set of rules and mechanisms by which all Bitcoin nodes independently agree on the valid state of the blockchain. Consensus rules define which blocks and transactions are valid, ensuring network-wide agreement without a central authority.

ReorgProtocolo

A blockchain reorganization that occurs when a node discovers a longer valid chain and switches to it, abandoning its previous chain tip. Reorgs can cause recently confirmed transactions to become unconfirmed, which is why multiple confirmations provide greater security.