<p>Simply put, a so-called <strong>hard fork</strong> is a change of the Bitcoin protocol that is not backwards-compatible; i.e., older client versions would not accept blocks created by the updated client, considering them invalid. Obviously, this can create a blockchain fork when nodes running the new version create a separate blockchain incompatible with the older software. </p>

<p>For potential future changes that would require a hard fork, see the associated <a href="https://en.bitcoin.it/wiki/Hardfork_Wishlist">wiki page</a>.</p>

CC BY-SA 3.0
2016-11-28T16:09:54.637Z
Should 'hard fork' not be constrained to Bitcoin protocol, and strictly define a condition in a blockchain network where node consensus diverges permanently.
Goddard
CC BY-SA 3.0
2016-11-28T16:17:50.740Z
What do you mean? The answer of BinaryMage mentions "is a change of the Bitcoin protocol".
Murch
CC BY-SA 3.0
2016-11-28T16:33:19.373Z
He meant limiting the definition to Bitcoin is unnecessarily restrictive. Ethereum has had hard forks too, and @BinaryMage's description of what a hard fork is would work equally well there, except for the fact that Ethereum doesn't use the Bitcoin protocol.
Nik Bougalis
CC BY-SA 3.0
2017-10-26T09:46:05.297Z
I think you mean HF is not forward-compatible. It *is* BWC in the sense that "the new understands the old" which is the common definition in most dictionaries.
jiggunjer
CC BY-SA 3.0
2013-04-05T10:49:43.480Z
2013-04-05T10:49:43.480Z
BinaryMage
<p>When people talk about possible changes to how Bitcoin works they sometimes say a particular change would require a hard fork. What does that mean? Can a hard fork cause problems?</p>

CC BY-SA 3.0
2015-01-30T23:02:28.077Z
related: [What is a soft fork?](http://bitcoin.stackexchange.com/questions/30817/what-is-a-soft-fork)
morsecoder
CC BY-SA 3.0
2017-03-27T19:40:53.750Z
Will Hard fork affect Bitcoin value to decrease?
I mean due to Blockchain split
Salvator NKUNZIMANA
<blockchain><blockchain-fork>
What is a hard fork?
Dr.Haribo
# What is a hard fork?

(Asked by: username_0 on 2013-04-05)

When people talk about possible changes to how Bitcoin works they sometimes say a particular change would require a hard fork. What does that mean? Can a hard fork cause problems?

**Tags:** blockchain, blockchain-fork

> **Comments:**
> **username_1**: related: [What is a soft fork?](http://bitcoin.stackexchange.com/questions/30817/what-is-a-soft-fork)  
> **username_2**: Will Hard fork affect Bitcoin value to decrease? I mean due to Blockchain split  

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## 1 answers

### Answer by username_3 on 2013-04-05. Score: 21 | Accepted answer

Simply put, a so-called **hard fork** is a change of the Bitcoin protocol that is not backwards-compatible; i.e., older client versions would not accept blocks created by the updated client, considering them invalid. Obviously, this can create a blockchain fork when nodes running the new version create a separate blockchain incompatible with the older software.

For potential future changes that would require a hard fork, see the associated [wiki page](https://en.bitcoin.it/wiki/Hardfork_Wishlist).

> **Comments:**
> **username_4**: Should 'hard fork' not be constrained to Bitcoin protocol, and strictly define a condition in a blockchain network where node consensus diverges permanently.  
> **username_5**: What do you mean? The answer of username_3 mentions "is a change of the Bitcoin protocol".  
> **username_6**: He meant limiting the definition to Bitcoin is unnecessarily restrictive. Ethereum has had hard forks too, and @username_3's description of what a hard fork is would work equally well there, except for the fact that Ethereum doesn't use the Bitcoin protocol.  
> **username_7**: I think you mean HF is not forward-compatible. It *is* BWC in the sense that "the new understands the old" which is the common definition in most dictionaries.  

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