Bitcoin Tutorials - Herong's Tutorial Examples - v1.04, by Dr. Herong Yang
Controlled Supply Rule - Total of 21M BTC
This section describes what is the Bitcoin Controlled Supply Rule - There will be only 21M BTC in total.
One important Bitcoin Consensus Rule is the Controlled Supply Rule: Total supply of Bitcoins is controlled to a fixed number of 21 million Bitcoins.
The 21-million-Bitcoin supply limit is set by the Bitcoin founder, Satoshi Nakamoto, who did not give any explanations.
One possible reason is that 21 million is close to the maximum capacity of a 64-bit floating point number in the smallest unit of Bitcoin, 1 Satoshi = 0.00000001 BTC.
In other words, if the total Bitcoin supply is 21,000,000.00000000, we safely use 64-bit floating point number format to record and calculate any Bitcoin amount in the range of 0.00000001 BTC and 20,999,999.99999999 BTC. Overflow or underflow will never happen.
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