In addition to the transaction ledger, each block typically contains some additional metadata. The metadata includes the following:
- A reference to the prior block
- Metadata about the network
- The Merkle root of the transactions, which acts as a check of the validity of the block
These basics tend to be common for all blockchains. Ethereum, Bitcoin, Litecoin, and others use this common pattern, and this pattern is what makes it a chain. Each chain also tends to include other metadata that is specific to that ecosystem, and those differences will be discussed in future chapters. Here is an example from the Bitcoin blockchain:
By Satoshi Nakamoto: http://Bitcoin.org/Bitcoin.pdf, MIT, https://commons.wikimedia.org/w/index.php?curid=24542868
If you are asking, What is a Merkle root?, that brings us to our next set of key concepts: hashing and signature.
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