<p>Solo miners and pool operators need a copy of the entire blockchain in order to verify new transactions against the transaction history. </p>

CC BY-SA 3.0
2018-03-21T01:27:22.650Z
That's incorrect. You don't need a copy of the full blockchain in order to fully validate new transactions/blocks. Look up pruning mode.
Pieter Wuille
CC BY-SA 3.0
2018-03-21T01:07:08.307Z
2018-03-21T01:07:08.307Z
meeow
<p>Running a full node (downloading the blockchain) allows a user to interact with the network, without having to trust any other network participant. </p>

<p>For some users, this may not be important, but for many users it is very important. For example:</p>

<ul>
<li>You are a business, and you need to ensure that txs you send and receive are in fact being communicated across the entire network.</li>
<li>You run an exchange, and want to make sure large deposits are not going to be double spent or orphaned</li>
<li>You hold a large amount of cryptocurrency, and want to maintain security and privacy of your funds</li>
<li>You live somewhere with heavy financial/economic restrictions, so access to webwallets, etc is banned outright. So to interact with the network you have to run your own node. </li>
<li>You are a believer in the philosophies behind cryptocurrency, and want to run a node just to help the network grow and remain robust.</li>
</ul>

<p>This is not an exhaustive list, I'm sure there are more reasons than I have listed. In general it is important that users remain capable of running their own nodes, as otherwise they will have to trust someone else to do so for them.</p>

CC BY-SA 3.0
2018-03-21T01:28:21.607Z
You're answering why someone may want to run a fully validating node, but that doesn't imply storing a copy of the blockchain.
Pieter Wuille
CC BY-SA 3.0
2018-03-21T03:58:02.797Z
@PieterWuille fair point, but even a pruned node must download the blockchain and then prune, correct? I interpreted the question as being  "why full node? versus SPV / webwallet /etc."
chytrik
CC BY-SA 3.0
2018-03-21T16:58:42.913Z
Given that the question worries about "a copy of the blockchain" and illegal data in it, I'm not sure. A non-validating client may also download the whole chain (for privacy), and a validating one does not need to store it.
Pieter Wuille
CC BY-SA 3.0
2018-03-20T22:06:33.727Z
2018-03-20T22:31:46.397Z
2018-03-20T22:31:46.397Z
chytrik
<p>As discussed in <a href="https://bitcoin.stackexchange.com/q/72679/80217">this question</a> there is a <a href="https://www.theguardian.com/technology/2018/mar/20/child-abuse-imagery-bitcoin-blockchain-illegal-content" rel="nofollow noreferrer">news report</a> today saying that researchers have found illicit files and information stored in the blockchain.</p>

<p>In today's Bitcoin world, who needs the full block chain?  With mining pools and online wallets looking like the norm (is this true?), do many people at all download the entire chain, or at least large portions of it?  I'm sure that researchers will download it in full, but what are the other use cases?  Does it extend at all to any casual users?</p>

CC BY-SA 3.0
2018-03-20T20:59:24.010Z
I really have not much of a clue of how exactly the technology works behind the scenes, but at the point where you (the user) don't decide yourself which parts to download (which you would have individually checked as legal before, of course), there is always the possibility that you could get illegal content by chance, even if you don't download the entire chain. Of course, if some mechanism could be derived to prevent such kind of misuse in the future, it would be enough to once find all such illegal content and always specifically exclude it from downloads.But I'm unsure if this is solvable
SK19
<blockchain><user-data>
Who needs a copy of the entire blockchain these days?
JPhi1618
# Who needs a copy of the entire blockchain these days?

(Asked by: username_0 on 2018-03-20)

As discussed in [this question](https://bitcoin.stackexchange.com/q/72679/80217) there is a [news report](https://www.theguardian.com/technology/2018/mar/20/child-abuse-imagery-bitcoin-blockchain-illegal-content) today saying that researchers have found illicit files and information stored in the blockchain.

In today's Bitcoin world, who needs the full block chain? With mining pools and online wallets looking like the norm (is this true?), do many people at all download the entire chain, or at least large portions of it? I'm sure that researchers will download it in full, but what are the other use cases? Does it extend at all to any casual users?

**Tags:** blockchain, user-data

> **Comments:**
> **username_1**: I really have not much of a clue of how exactly the technology works behind the scenes, but at the point where you (the user) don't decide yourself which parts to download (which you would have individually checked as legal before, of course), there is always the possibility that you could get illegal content by chance, even if you don't download the entire chain. Of course, if some mechanism could be derived to prevent such kind of misuse in the future, it would be enough to once find all such illegal content and always specifically exclude it from downloads.But I'm unsure if this is solvable  

---

## 2 answers

### Answer by username_4 on 2018-03-20. Score: 4 | Accepted answer

Running a full node (downloading the blockchain) allows a user to interact with the network, without having to trust any other network participant.

For some users, this may not be important, but for many users it is very important. For example:

* You are a business, and you need to ensure that txs you send and receive are in fact being communicated across the entire network.
* You run an exchange, and want to make sure large deposits are not going to be double spent or orphaned
* You hold a large amount of cryptocurrency, and want to maintain security and privacy of your funds
* You live somewhere with heavy financial/economic restrictions, so access to webwallets, etc is banned outright. So to interact with the network you have to run your own node.
* You are a believer in the philosophies behind cryptocurrency, and want to run a node just to help the network grow and remain robust.

This is not an exhaustive list, I'm sure there are more reasons than I have listed. In general it is important that users remain capable of running their own nodes, as otherwise they will have to trust someone else to do so for them.

> **Comments:**
> **username_3**: You're answering why someone may want to run a fully validating node, but that doesn't imply storing a copy of the blockchain.  
> **username_4**: @PieterWuille fair point, but even a pruned node must download the blockchain and then prune, correct? I interpreted the question as being  "why full node? versus SPV / webwallet /etc."  
> **username_3**: Given that the question worries about "a copy of the blockchain" and illegal data in it, I'm not sure. A non-validating client may also download the whole chain (for privacy), and a validating one does not need to store it.  

---

### Answer by username_2 on 2018-03-21. Score: -2

Solo miners and pool operators need a copy of the entire blockchain in order to verify new transactions against the transaction history.

> **Comments:**
> **username_3**: That's incorrect. You don't need a copy of the full blockchain in order to fully validate new transactions/blocks. Look up pruning mode.  

---

