BA-08 · LESSON 14

Soft forks, hard forks, and compatibility

Run one block through old and new rule sets to see subset restrictions, rule expansions, activation risk, and persistent chain splits.

45 min Difficulty 3/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · fork compatibilityOld and new nodes can disagree on the same blockSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
SAME BLOCKNew restriction case
Both node versions receive identical bytes and context.
02
OLD NODEAccept
The old node applies only its installed acceptance rules.
03
NEW NODEReject
The new node applies the changed rule set locally.
04
RELATIONSoft-fork violation
Old-valid can lie outside the stricter new set.
05
RISKIncompatible branches
Hash power and economic coordination affect persistence, but not each node's validity result.

Rule shown: A soft fork restricts new-valid blocks to a subset of old-valid blocks; a hard fork permits at least one new-valid block that old nodes reject.

STAGE 1 OF 5SAME BLOCK: New restriction case

Both node versions receive identical bytes and context.

Governing relationship: A soft fork restricts new-valid blocks to a subset of old-valid blocks; a hard fork permits at least one new-valid block that old nodes reject. Complete path: 1. SAME BLOCK, New restriction case. Both node versions receive identical bytes and context. 2. OLD NODE, Accept. The old node applies only its installed acceptance rules. 3. NEW NODE, Reject. The new node applies the changed rule set locally. 4. RELATION, Soft-fork violation. Old-valid can lie outside the stricter new set. 5. RISK, Incompatible branches. Hash power and economic coordination affect persistence, but not each node's validity result.

1. State transitionWhat exists, what changes, and what results

BEFORE

Change A rejects a Script form old nodes accept. Change B permits a larger object old nodes reject.

MECHANISM

State the old acceptance set and the new acceptance set precisely. Labels such as upgrade or fork do not reveal their compatibility relationship.

AFTER

Compatibility is a relationship between acceptance sets; deployment is the separate problem of coordinating people and software around it.

Text equivalent: Starting from Change A rejects a Script form old nodes accept. Change B permits a larger object old nodes reject. The mechanism begins when State the old acceptance set and the new acceptance set precisely. Labels such as upgrade or fork do not reveal their compatibility relationship. The resulting lesson is Compatibility is a relationship between acceptance sets; deployment is the separate problem of coordinating people and software around it.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Write both rule sets

State the old acceptance set and the new acceptance set precisely. Labels such as upgrade or fork do not reveal their compatibility relationship.

Complete path: 1. Write both rule sets: State the old acceptance set and the new acceptance set precisely. Labels such as upgrade or fork do not reveal their compatibility relationship. 2. Test one block twice: Run identical bytes and chain context through an old node and a new node. Record whether each independently accepts or rejects. 3. Recognize the soft-fork subset: New-valid is a subset of old-valid. The dangerous block is old-valid but new-invalid; non-upgraded miners can build a branch upgraded nodes refuse. 4. Recognize hard-fork expansion: At least one new-valid block is old-invalid. Once that block appears, old nodes cannot follow the new chain without changing their rules. 5. Separate deployment from safety: Hash power, node adoption, economic coordination and activation design affect which branches persist. They do not change the mathematical compatibility relation between rule sets.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

Every node follows its installed rules and selected valid most-work branch; no signaling label makes an incompatible block valid to that node.

CHANGED CONDITION

Calling any coordinated change backward compatible, or assuming majority hash power rewrites old node validity, hides the actual split condition.

Important distinction: A hard fork simply means a controversial software release. Hard describes rule compatibility: new rules accept at least one block old rules reject. A change can be popular and still be a hard fork, or contentious and still use soft-fork compatibility.

Text equivalent: The accepted path is enforced by Every node follows its installed rules and selected valid most-work branch; no signaling label makes an incompatible block valid to that node. If the required condition changes, Calling any coordinated change backward compatible, or assuming majority hash power rewrites old node validity, hides the actual split condition.

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Learn the idea

A consensus change matters because old and new nodes can make different decisions about the same block. A soft fork tightens the rules, so every block accepted by new nodes is also acceptable to old nodes. A hard fork expands or otherwise changes acceptance so at least one block accepted by new nodes is rejected by old nodes.

GUIDED EXPLANATION1/5 ideas inspected

Write both rule sets

State the old acceptance set and the new acceptance set precisely. Labels such as upgrade or fork do not reveal their compatibility relationship.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“A hard fork simply means a controversial software release.”

Hard describes rule compatibility: new rules accept at least one block old rules reject. A change can be popular and still be a hard fork, or contentious and still use soft-fork compatibility.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.