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Bitcoin

Bitcoin is digital money that people can send to each other online without a bank or payment company in the middle. The rules are enforced by open-source software run by thousands of independent computers.

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It was published under the pseudonym Satoshi Nakamoto, whose identity is still unknown. No company or government runs it: anyone can run the software, and a rule change only sticks if the people running it choose to adopt it.

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Transactions are grouped into blocks, and each block links to the one before it, forming the blockchain. Miners compete to add the next block using proof-of-work, at a target of about six blocks an hour. Nodes independently check every block against the rules and reject anything invalid.

Next step: The white paper, summarized →

People value it for being scarce, portable and hard to censor or seize; like any money, its price depends on what others will pay. New bitcoin is issued on a fixed schedule that halves every 210,000 blocks, so the total can never exceed 21 million.

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The block subsidy started at 50 BTC and halves every 210,000 blocks (Bitcoin Core GetBlockSubsidy, validation.cpp; interval set in chainparams.cpp), a geometric series that sums to about 21 million. Every full node enforces this and rejects any block that pays its miner more than the subsidy plus fees, so changing it would need nearly everyone to voluntarily run different software (white paper, sections 5-6). Because rewards are whole satoshis and each halving rounds down, the true maximum is 20,999,999.9769 BTC, with the last subsidy paid around 2140. Go deeper: supply schedule · course module: Issuance and the halving.

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No. A satoshi (sat) is the smallest unit: one hundred millionth of a bitcoin (0.00000001 BTC)). You can buy any fraction, such as a few dollars' worth.

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