Academy School · Chapter 3 of 14
Bitcoin Consensus & Mining
How Bitcoin secures transactions and why proof of work matters.
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Return to Academy SchoolProof of Work Basics
Proof of work secures Bitcoin by requiring real computational effort to create blocks. Miners compete to solve a puzzle, and that cost makes rewriting history expensive.
The important idea is not the puzzle itself, but the economic barrier it creates. A malicious actor must spend real resources to challenge the chain, which raises the price of attack.
- Blocks require computational effort.
- Security comes from real cost.
- Attackers must outspend the network.
Proof of work turns energy cost into network security.
Difficulty and Hashrate
Difficulty adjusts so block timing stays roughly stable even as mining power changes. If more miners join, the puzzle becomes harder; if miners leave, it becomes easier.
Hashrate measures the total computational power securing the network. Higher hashrate usually means a larger cost for an attacker, although security still depends on many factors.
- Difficulty keeps block timing stable.
- Hashrate reflects network security power.
- More cost usually means stronger defense.
Difficulty and hashrate together help keep Bitcoin predictable and secure.
Transactions, Blocks, and Finality
Transactions first appear in the mempool before being included in a block. Once included, each additional confirmation makes reversal less likely, though never mathematically impossible.
Bitcoin finality is probabilistic rather than instant. That design is normal for open consensus systems and is one reason users wait for multiple confirmations before treating a payment as settled.
- Mempool comes before block inclusion.
- Confirmations increase confidence.
- Finality is probabilistic, not absolute.
More confirmations mean more confidence, not magical certainty.
Why Mining Economics Matter
Miners are paid by block rewards and transaction fees. Those incentives shape how much equipment is deployed, where it is deployed, and how hard the network is to attack.
Mining economics matter because security is not abstract. It depends on participants having enough reason to honestly maintain the chain instead of trying to break it.
- Miner income comes from rewards and fees.
- Incentives shape network behavior.
- Security depends on honest participation.
Bitcoin security is an economic system as much as a technical one.
Further reading