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A full node is a node with the whole blockchain and is able to verify any new incoming blocks.

A pruned node, is a node with only some of the blockchain, namely it has removed some of the older blocks due to space requirements. A pruned node cannot validate blocks, as it does not have the full history of the blockchain right? So how can we still say that it is a full node?

Am I also right in saying that they do not serve any value to the network, as any blocks they send out will not be fully validated?

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Pruned nodes will verify new blocks and they are classified as full nodes

  • They keep the complete database of all UTXOs. This is enough to verify new blocks. What is required for validation is that the tx in the new blocks are spending only the current unspent transaction outputs
  • They store mempool and check blocks to make sure they comply with all bitcoin protocol rules, just like other nodes
  • Since, they don't keep older block data, only thing that they can't do is to return older block data to other nodes. They still keep latest block data for reogranization, which they can share with other nodes
  • So is it possible to start up the bitcoin network, and download all UTXOs then be classed as a pruned node? Or do i need to first be a full node and then activate pruning mode? In the former, I would not have previously verified the whole blockchain myself – Kyle Graham Mar 20 '18 at 10:47
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    It is theoretically possible to download all UTXO an be a node. You need to also download all block headers to find out the longest chain. However, in current bitcoin protocol there is no provision to fetch UTXOs, so you need to download all blocks from starting to build the UTXO database or you can copy UTXO from another trusted node. – dark knight Mar 20 '18 at 11:24
  • I understand now. Thanks for the clear and concise answer – Kyle Graham Mar 20 '18 at 11:52

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