<p>Every time Bitcoin is forked, the blockchain is forked too, thus creating a different blockchain. This applies to all cryptocurrencies that were forked from bitcoin.</p>

<p>Even the main Bitcoin branch has at least two different blockchains: one has real value because it's expensive to mine bitcoin there, the other is the test blockchain (testnet), where bitcoins are easily created, thus they have no value.</p>

CC BY-SA 4.0
2019-10-30T08:00:11.857Z
The mainnet and testnet are completely separate chains, they do not share any blocks. Forks are only chains that have some common block history leading up to the genesis blocks.
Raghav Sood
CC BY-SA 4.0
2019-10-30T07:52:22.440Z
2019-10-30T07:52:22.440Z
Sasino
<p>The Bitcoin blockchain converges to a single-file chain because each block references exactly one predecessor, and thus there can only be one block at every height in the chain connecting the genesis block and the chain-tip.</p>

<p>However, at times more than one block will be found at the same height. This happens either due to the mere happenstance of two miners discovering a valid block in the same instant, which is benign and will rectify by itself when one of the two sires a successor block and thus creates a new longest valid chain, or it could happen if a faction in Bitcoin adopts an incompatible protocol rule change (hardfork). Since network participants that don't accept the rule change will not accept these blocks as valid, two chain-tips may persist henceforth. </p>

<p>Recently, the hardfork plans of Bitcoin Unlimited have been a major topic in Bitcoin, which frequently includes discussion of possible scenarios with two incompatible chain-tips. I assume that you seeing a discussion of that sort gave you the idea that there could be more than one chain.</p>

CC BY-SA 3.0
2017-03-20T08:02:06.867Z
2017-03-20T09:09:08.977Z
2017-03-20T09:09:08.977Z
Murch
<p>Is each block found just a link in the same long chain, or are there multiple chains?</p>

<blockchain><best-chain>
Is bitcoin just one long block chain or are there multiple chains?
Deekor
# Is bitcoin just one long block chain or are there multiple chains?

(Asked by: username_0 on 2017-03-20)

Is each block found just a link in the same long chain, or are there multiple chains?

**Tags:** blockchain, best-chain


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## 2 answers

### Answer by username_3 on 2017-03-20. Score: 5 | Accepted answer

The Bitcoin blockchain converges to a single-file chain because each block references exactly one predecessor, and thus there can only be one block at every height in the chain connecting the genesis block and the chain-tip.

However, at times more than one block will be found at the same height. This happens either due to the mere happenstance of two miners discovering a valid block in the same instant, which is benign and will rectify by itself when one of the two sires a successor block and thus creates a new longest valid chain, or it could happen if a faction in Bitcoin adopts an incompatible protocol rule change (hardfork). Since network participants that don't accept the rule change will not accept these blocks as valid, two chain-tips may persist henceforth.

Recently, the hardfork plans of Bitcoin Unlimited have been a major topic in Bitcoin, which frequently includes discussion of possible scenarios with two incompatible chain-tips. I assume that you seeing a discussion of that sort gave you the idea that there could be more than one chain.


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### Answer by username_1 on 2019-10-30. Score: 0

Every time Bitcoin is forked, the blockchain is forked too, thus creating a different blockchain. This applies to all cryptocurrencies that were forked from bitcoin.

Even the main Bitcoin branch has at least two different blockchains: one has real value because it's expensive to mine bitcoin there, the other is the test blockchain (testnet), where bitcoins are easily created, thus they have no value.

> **Comments:**
> **username_2**: The mainnet and testnet are completely separate chains, they do not share any blocks. Forks are only chains that have some common block history leading up to the genesis blocks.  

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