Course Content
Introduction to Blockchain
3. Advanced Blockchain Concepts
Introduction to Blockchain
Blockchain Structure
Congratulations, you are now familiar with the basics of blockchain technology and Bitcoin in particular, so we are ready to explore the detailed structure of a blockchain based on the Bitcoin model.
Block Components
A blockchain is, in its simplest form, a chain of blocks. However, these are not physical "blocks" but rather digital records that are linked together.
Let's take a look at the following table which illustrates the general structure of a block in the Bitcoin blockchain:
| Field | Description | Size |
|---|---|---|
| Block Size | The size of the block in bytes, indicating the amount of data it contains | 4 bytes |
| Block Header | Contains metadata about the block | 80 bytes |
| Transaction Counter | The total number of transactions included in the block, represented in a variable length integer format | 1-9 bytes |
| Transactions | A list of all individual transactions included in the block | Variable |
You don't have to memorize the size of each field, they are simply provided for better understanding. Speaking of sizes, below is an explanation of what bits and bytes actually are:
Block Header
Perhaps, the most important part of each block is its header which is made up of 6 fields. Below is an illustration of a more detailed block structure (Txn_count and txns stand for transaction counter and transactions, respectively, which are not a part of the header):
Let's now go through each of the fields of the block header:
| Field | Description | Size |
|---|---|---|
| Version | The version of the blockchain protocol in use (the set of block validation rules that a block follows) | 4 bytes |
| Previous Block Hash (Previous_hash) | A hash (unique identifier) of the previous block's header, which ensures the continuity of the chain | 32 bytes |
| Merkle Tree Root (Merkle_root) | A single hash that represents all the transactions included in the block | 32 bytes |
| Timestamp | The time when the block was created | 4 bytes |
| Bits | A compact representation of the target threshold that the block's hash must meet in order to be added to the blockchain | 4 bytes |
| Nonce | A number that miners change to get the resulting block hash which meets the difficulty target | 4 bytes |
Don't worry, we'll go through most of these fields in more detail later in the course. For now, let's take a look at a real block using a Blockchain Explorer (here is the link):
As you can see, all the components we have discussed are present in this block.
There are also additional details (you can disregard them for now) provided by the blockchain explorer:
- Height;
- Status;
- Virtual Size;
- Weight Units.
These fields provide context about the block's status within the blockchain, its size, and resource usage.
Which of the following is NOT a part of the block header?
Select the correct answer
Everything was clear?
