Blockchain Essentials
Everything you need to know about blockchains before diving into Subtensor. If you're already comfortable with blocks, state, and consensus, feel free to skip to the next page.
What is a blockchain?
A blockchain is a shared database that no single party controls. Instead of one company storing your data on their servers, a network of independent computers (called nodes) each maintain an identical copy.
Changes to this database are grouped into blocks. Each block references the one before it, forming a chain, hence "blockchain." Because every node validates every block, nobody can secretly alter the history.
What's in a block?
Each block contains three things:
Header
Metadata about the block: its number, timestamp, a hash of the previous block (the "chain" link), and a hash of the current state.
Extrinsics (transactions)
The actual operations: transfers, staking, configuration changes. In Substrate-based chains like Subtensor, these are called extrinsics because they come from outside the chain.
State root
A cryptographic fingerprint of the entire database after this block's transactions have been applied. This lets anyone verify the state is correct.
State: the blockchain as a database
At its core, a blockchain is a key-value database. It stores things like:
- Account balances (who has how much TAO)
- Staking relationships (who staked on whom)
- Network configuration (subnet parameters, weights)
Every transaction is a state transition: it reads some values, checks some rules, and writes new values. The block is what groups those transitions and makes them permanent.
Consensus in 30 seconds
If many nodes each maintain a copy of the database, how do they agree on what's true? That's consensus.
Subtensor uses a Proof of Authority (PoA) model with two protocols working together. Aura handles block production: a set of trusted authority nodes take turns proposing new blocks every 12 seconds. GRANDPA handles finality: the authorities vote on which blocks are permanent. Once enough authorities agree, a block is finalized, meaning it becomes irreversible history.
Every node on the network independently verifies every block it receives, checking that all transactions follow the rules and state transitions are correct. Invalid blocks are rejected. The authorities' special role is producing and finalizing blocks, not verification.
Note on "validators": In the Bittensor ecosystem, "validator" usually refers to subnet validators who evaluate miner work. The blockchain-level block producers are called authorities, a separate role entirely.
The Blockchain Primer covers cryptography, P2P networks, consensus algorithms, and the Substrate framework in detail.