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Blockchain works in a decentralized way, which means that there is no central authority to control anything. This makes it censor-resistant and hack-proof because miners verify the data. Miners run some kind of software on their system to compute hashes and verify transactions.
These miners run a blockchain node on their System which contains all the blockchain info starting from the genesis block(first block). A node is a complete copy of all the transactions that occurred on the blockchain. These nodes are verified and they keep track of all the transactions on the blockchain.
Different Types of Nodes
Let’s Go deeper !!
Stores a complete copy of all blockchain transactions.
These nodes can validate new blocks in the transaction as they participate in voting with other nodes for approving a transaction.
Holds the complete state of the chain from the genesis block.
Lightening or Light Nodes
Light nodes don't hold the complete blockchain data. Instead, they only store the block headers which are similar to the index of a block.
Whenever a Dapp needs data, it fetches it from the full node using the block header.
These nodes store the complete data of the Full node + build an archive of historical data.
This is a lot of data(in many TBs) that’s not much use but block explorers need to maintain all this.
This data is also useful in chain analytics.
Blockchain nodes are expensive to run and this is why miners are being rewarded for their efforts. The fees that you pay towards are the network are distributed among miners.