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Bitcoin works through a sequence of signed transactions, independent rule checks and proof-of-work blocks. A wallet authorizes a payment with a private-key signature; network participants verify that it spends valid, unspent outputs; and miners compete to record valid transactions in a shared history. No central operator declares a payment valid, and a miner cannot make an invalid block acceptable to nodes that reject it.
How a Bitcoin payment moves through the network
- A wallet creates and signs a transaction. It selects earlier transaction outputs it can spend, then uses the relevant private key to authorize their spending. The transaction creates new outputs with conditions specifying who can spend them. The signature lets others verify authorization without trusting the sender’s assertion. Bitcoin.org’s overview of how Bitcoin works and the developer guide to transactions explain these basics.
- The transaction is broadcast. The sender shares the signed transaction with Bitcoin’s peer-to-peer network. Peers check it before relaying it; miners also check transactions they may include in a block.
- Participants validate the spend. They check that the referenced outputs are available and have not already been spent, and that the transaction satisfies the spending conditions. The total value of its outputs cannot exceed the value of its inputs. The difference, if any, can be claimed by the miner whose block includes the transaction as a fee.
- A miner includes it in a proposed block. Miners compete to find proof of work for a block. They propose blocks, but nodes independently check each proposed block against the rules they follow.
- More blocks build on the history. Each block refers to its predecessor. As later blocks add proof of work, replacing an earlier block requires redoing that work and the work for blocks built on top of it.
What Bitcoin tracks: spendable outputs, not account balances
Bitcoin does not maintain a central account ledger in which an operator updates each person’s balance. A transaction spends one or more existing outputs and creates new ones. Wallet software derives a displayed balance from outputs available to spend; the network’s transaction rules ensure an output can be spent only once. This model is known as the unspent transaction output (UTXO) model. Bitcoin’s developer documentation on the block chain describes the ledger and validation process.
For example, a wallet might use an output worth more than the intended payment. The transaction can create one output for the recipient and another returning the remainder to the sender, with any difference between total inputs and outputs available as the fee. The payment amount is not itself the basis for the fee; fees depend on demand for block space.
Why mining does not decide whether transactions obey the rules
Mining orders transactions by proposing blocks secured by proof of work. A miner searches for a block-header hash below the network’s current target. Finding one lets the miner propose a block; it does not give the miner authority to rewrite the rules. Nodes check the block themselves and reject it if it violates the rules they enforce. Bitcoin.org puts the principle plainly: “Every Bitcoin node in the world will reject anything that does not comply with the rules it expects the system to follow.” Bitcoin.org’s FAQ explains the distinction.
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This is why “consensus” does not mean a central authority approves transactions, or that miners can vote invalid transactions into validity. Independently validating participants converge on a history that follows their rules, with proof of work helping determine which valid history is accepted when competing block histories appear.
Difficulty responds to the network’s aggregate mining rate
The protocol recalculates mining difficulty every 2,016 blocks, using a target timespan of 1,209,600 seconds (two weeks). The adjustment uses block-header timestamps to respond to how quickly blocks were produced over the preceding interval. It is a mechanism for adapting to changes in aggregate hashing rate, not a guarantee that any individual block will arrive at a set time. The developer documentation on the block chain describes the adjustment.
What happens when miners find competing blocks
Two miners can find blocks close together. Different nodes may hear about different blocks first and temporarily have different chain tips. Nodes follow the valid chain with the most accumulated proof of work. When a later block extends one side, that side becomes the accepted history for nodes that receive it; the competing block becomes stale.
This process makes confirmation probabilistic rather than an instantaneous, absolute guarantee. Reversing a transaction in an older block would require replacing that block and catching up with the work accumulated after it. Each subsequent block generally increases the work an attacker would need to overcome, but does not make reversal mathematically impossible. Bitcoin’s developer guide explains block links, proof of work and chain selection.
How long does a Bitcoin confirmation take?
Bitcoin.org describes new blocks as arriving about every 10 minutes on average. That is an average, not a timer: no individual confirmation has a guaranteed minimum or maximum delay. A transaction can be visible to a recipient soon after broadcast, but a notification is not the same as inclusion in a confirmed block. Bitcoin.org’s FAQ covers block timing and confirmations.
A transaction’s fee relative to current demand for block space can affect how quickly miners include it. There is no live fee estimate here: fee levels change, and the protocol does not set a fixed fee based simply on the amount transferred.
Choosing a confirmation policy
There is no universally correct confirmation count for every payment. A recipient can weigh:
- Value and reversal risk: Higher-value payments may warrant waiting for more blocks to accumulate.
- Time sensitivity: A recipient deciding whether to release goods or provide a service may have different needs from one processing a payment with no immediate deadline.
- Fee relative to block-space demand: A fee that is less competitive when demand is high may mean a longer wait for initial inclusion.
- The recipient’s policy: The receiving party decides how many confirmations it requires for its circumstances.
Who controls Bitcoin and changes its rules?
No single owner or person can force a protocol change. Proposals are discussed publicly, often as Bitcoin Improvement Proposals (BIPs), and reviewed by developers. A proposed change takes effect only as users, miners and node operators voluntarily adopt compatible software. Bitcoin.org summarizes the governance point as: “No one person or group decides.” Its FAQ on protocol changes provides the context.
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Participants have different roles: developers can propose and maintain software, miners produce blocks, and node operators choose which rules their software enforces. A miner can propose a block, but cannot compel nodes to accept it if it breaks their rules.
How new bitcoins enter circulation
Under the current protocol’s programmed issuance rule, the amount of new bitcoin issued declines predictably until issuance reaches a total limit of 21 million bitcoins. The calendar year of the final issuance is not specified here. Bitcoin.org’s FAQ says transaction fees are expected to support miners after new issuance ends; that describes the protocol’s intended incentive structure, not a guarantee about future market prices or mining economics. Bitcoin.org’s FAQ on issuance explains the limit.
What a full node does—and what a wallet may not do
A full node downloads and independently validates blocks and transactions against its software’s rules. A wallet helps manage keys and create or display transactions, but not every wallet performs full validation itself. A miner searches for proof of work and proposes blocks; mining and full-node validation are distinct functions. Bitcoin’s developer guide describes these technical roles.
The original idea behind Bitcoin’s shared history
Bitcoin’s design draws on a timestamping approach: linking blocks makes later changes to recorded history visible and costly to carry through the proof-of-work chain. In the 2008 paper, Satoshi Nakamoto wrote: “The Times-Stamp Server works by taking a hash of a block of items to be timestamped and widely publishing the hash”. Read the original Bitcoin paper for the proposal in its original form.
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