Excluding the first block within a blockchain, also referred to as the genesis block, all subsequent blocks contain a hash, or digital signature, of the previous block.
Looking at our diagram, we can see that block number 2 contains a hash of block number 1, while block number 3 contains a hash of block number 2.
But what is the purpose of this? Well, by adding the hash of the previous block to the data, or records, of its subsequent block, the hash of the subsequent block is now partially based on the hash of it’s preceding block. And please note, we used the term partially, as each block contains its own records too.
And when this rule is followed for every block within a blockchain, you can see how all of the blocks are in fact not only linked to their preceding blocks, but also, to each and every other block that came before them, forming a truly linked chain of blocks, or, a blockchain.
Again this component of blockchain is at the heart of security, and we’ll learn why it is so, in our next module, Blockchain Security