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Somebody asked me about Bitcoin and I explained to him many many computers are connected to the Blockchain to keep records of all the accounts (or to keep addresses of the bitcoin and owner?). But how many computers are connected to it, as of recently or 2020?

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  • Note: the Blockchain doesn't keep records of accounts and doesn't keep track of owners. The Bitcoin network doesn't care about owners in the normal sense - it only cares about proofs of knowledge of private-keys corresponding to addresses. Anyone who can prove they know a key is allowed to spend associated money. Ownership of money in the Bitcoin network is not the same as legal ownership. Jan 29 at 12:07
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Somebody asked me about Bitcoin and I explained to him many many computers are connected to the Blockchain to keep records of all the accounts (or to keep addresses of the bitcoin and owner?).

The blockchain is the data structure they collectively maintain. It is not an "entity" that can be connected to. The nodes are just connected to each other, and tell each other about updates they learn about.

It's hard to count how many nodes there actually are. There are sites like https://bitnodes.io that keep track of reachable nodes. However, there are many nodes on the network that only connect out to others but can't be connected to; probably in the 100000s.

A further complication is that not all of these nodes are equally relevant. It's easy to spin up a few hundred nodes on AWS, that nobody uses for anything, but do make it look like there are lots of independent users. Worse, there are also a lot of spy nodes on the network that don't do any work, except trying to monitor which nodes are the origin of particular transactions.

In the end, if you run a node yourself, it doesn't matter. It validates everything the network tells it, so if you do that, the part that matters is: 1 node, your own.

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  • I added up the "11476 Bitcoin Core nodes" on coin.dance/nodes with the other nodes and that number is less than 20,000... could that means less than 20,000 nodes? Jan 29 at 3:19
  • These sites only count reachable nodes. It is very hard to know the actual numbers of others. None of these sites are authoritative. It's just fundamentally hard to know about unreachable nodes. Jan 29 at 3:36
  • @deeper-understanding 83120 Bitcoin Core nodes and more nodes for other implementations according to luke.dashjr.org/programs/bitcoin/files/charts/software.html Also refer to this answer: bitcoin.stackexchange.com/a/98821 and I agree with Pieter every website uses its own strategy to crawl and get the numbers
    – Prayank
    Jan 29 at 5:01
  • If it is 83120 nodes... or say, 100,000 nodes, then does that mean one country can just buy 50,000 Raspberry Pi, which would be 50,000 x US$50 = US$2.5 million and be able to become the 51%? It they spend $2.5 million and can steal $20 million, that's immediately very profitable Jan 29 at 10:48
  • Full node ! = Miner bitcoin.stackexchange.com/questions/59220/… and 51% attack is more than just getting hashpower. Some of the game theory is already mentioned in your previous question: bitcoin.stackexchange.com/a/101922
    – Prayank
    Jan 29 at 13:49
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Computers are not 'connected to the blockchain', as that implies that the blockchain is some sort of central entity in the network.

In reality, the network is just made up of a huge number of peers, known as 'nodes'. A 'full node' is one which has fully verified the state of the network, by working to verify all transactions that have occurred since the genesis block.

So each node keeps its own copy of the blockchain, and is connected to other nodes, which each have their own copy as well. The rules of the network work to allow these nodes to all remain in consensus about what that blockchain looks like, despite the fact they each keep their own record of it.

How many nodes are there? It's tough to say. Many nodes are made to be intentionally hidden, for security or privacy reasons. Many exist on the tor network, and some receive their information via satellite feed. Some websites will query nodes on the network in an attempt to figure out numbers, but ultimately the answer to this question is not really knowable for certain.

See for example:

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