Blockchain Data Structure

What is blockchain? #

In a blockchain system, data is stored in blocks of transactions. The most common definition is as follows:

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A timestamped log of transactions that is replicated on multiple peers.

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Distributed Consensus #

Now, some of these peers might be evil and intentionally report a tampered version of blockchain data. The entire network uses democracy to come to a consensus on the current state of data and any non-conformant or outlier peers are ignored/blocked.

This means that in order for a blockchain network to be fair and valid, most of the nodes have to be fair. If 51% of the nodes are compromised the network is hacked. Since the networks are globally distributed, this is not a possibility.

Data Storage in Blocks #

Let’s see how blockchain stores data in blocks. Each block stores a data blob(which is usually a list of transactions), its block number, and hash of the previous block:

Each block is represented by a json object here for better understanding: