# Secret of Bitcoin II : Proof of Work
## Review ##
In previous article Secret of Bitcoin I, I have explained details of bitcoin transaction. Now I am going to explain why bitcoin technology can support transactions in such great volume--mining and proof of work.
## Outline ##
Review
Node Operator and Hashrate Operator
Hashrate and Security
Game of Nodes
Conclusion
## Node Operator and Hashrate Operator ##
Bitcoin mining is an expensive market signal. To make it more clear, we will discuss
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