Mechanics
How Bitcoin actually works
No jargon you don't need. Every number on the clock is a live readout of one of the moving parts below — this page is where you find out what each of them is doing.
Follow one payment, step by step
Press play — or click any step yourself — and follow a single transaction from a wallet all the way to a block nobody can rewrite.
- 01 · You
- 02 · Mempool
- 03 · Miners
- 04 · Blockchain
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Step 1
You sign the payment
Your wallet signs the transaction with your private key — proof that you are allowed to spend these particular coins. Nothing leaves your device unsigned, and the key itself never leaves at all.
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Step 2
It is broadcast to the network
The signed instruction is passed to the peers your wallet is connected to — which may be anywhere in the world, not nearby in any physical sense. Each one checks it independently: the signature matches, and the coins have not already been spent.
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Step 3
It waits in the mempool
Valid transactions queue here, ranked by the fee they offer. Block space is limited, so this is an auction, not a queue by arrival time. Right now roughly 4,200 transactions are waiting, and the going rate for a fast one is about 9 sat/vB.
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Step 4
Miners race to seal it into a block
Miners bundle the highest-fee transactions into a candidate block, then guess numbers until the block's fingerprint happens to start with enough zeros. It is trial and error, not calculation — about 890 quintillion guesses a second across the whole network. That is Proof-of-Work.
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Step 5
The block joins the chain
The winning block references the previous block's fingerprint, which is what makes it a chain: you cannot quietly change an old block without breaking every block after it. Every node re-checks the new block and stores the same copy. Your payment now has one confirmation.
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Step 6
Confirmations make it final
Each new block stacked on top buries yours deeper. After about six, undoing it would mean out-working the entire rest of the network — so at that point the payment is treated as settled. Before the first confirmation it is not settled at all, only waiting.
Mining is guessing, not maths
This is the part almost every explanation gets wrong. Miners are not solving equations, and they are not doing science. They are turning the dial on a combination lock.
A miner takes the block they want to publish and runs it through a one-way function that produces a fingerprint — a fixed-length string of characters. Change one tiny thing about the block and the fingerprint changes completely and unpredictably. The network's rule is simply: the fingerprint must start with a certain number of zeros. There is no way to work backwards to an input that produces one. The only method is to change a throwaway number in the block, look at the new fingerprint, and try again.
Why bother? Because guessing costs electricity, and the guessing is the whole point. To rewrite an old block you would have to redo its guessing, and the guessing of every block after it, faster than the rest of the world is adding new ones. The waste is the lock.
The moving parts
Six ideas. Once these land, every number on the clock reads as a sentence.
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Proof-of-Work
Mining and the reward
Miners race to guess a number that makes a block's fingerprint valid. The winner adds the block and collects the reward plus the fees inside it. This deliberately wasteful work is exactly what makes cheating expensive.
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Difficulty
Why a block takes about ten minutes
A self-adjusting difficulty keeps blocks landing every ten minutes on average. Every 2,016 blocks it recalculates: if mining got faster, the puzzle gets harder. No central clock — just arithmetic holding the pace steady.
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Mempool & fees
Why fees rise when it is busy
Blocks hold limited space, so pending transactions queue and bid for entry in satoshis per virtual byte. Pay more to jump the line. Today the fast rate is around 9 and the patient rate around 2.
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Confirmations
Blocks stack, and that is the security
Each block bundles transactions and references the one before it. Once yours is in a block it has one confirmation; every block on top adds another, and reversal gets exponentially harder. The chain is currently 962,524 blocks long.
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Halving
Why there will only ever be 21 million
New coins are created only as block rewards, and that reward halves every 210,000 blocks. The arithmetic guarantees the supply stops at 21 million — 94.9% of which has already been mined.
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Consensus
Everyone checks everyone
Thousands of independent nodes verify every block against the same rules. No single party can change the supply, reverse a payment or freeze an address — that shared agreement is the only authority there is.
If you want the whole stack
Everything above is the shape of it. These five layers are the same story told with the real names, for anyone who wants to go further. Open whichever you need.
1 · Identity and ownership
No names and no bank accounts — just cryptography.
- Private key
- A random 256-bit secret. It signs transactions to prove you own the coins.
- Public key
- Derived from the private key through elliptic-curve maths (secp256k1). It cannot be run backwards.
- Address
- The public key, hashed and encoded into the string you share to get paid — Base58 for older addresses, Bech32 for SegWit.
2 · Transactions and the UTXO model
Value moves as discrete coins, not as an account balance.
- Inputs and outputs
- A transaction spends existing coins (inputs) and creates new ones (outputs) — to the recipient, plus change back to you. There is no "balance" field anywhere.
- Locking and unlocking
- Each coin is locked by a script, usually to the recipient's key. To spend it you supply a signature that satisfies that script.
- What the signature covers
- A flag decides how much of the transaction the signature commits to. The usual one locks every input and output, so nothing can be altered afterwards.
3 · The peer-to-peer network
Your signed transaction is handed to the world.
- Mempool
- Every node validates the transaction — signature valid, coins not already spent — and holds it in memory, waiting for a block.
- Propagation
- Nodes relay transactions and blocks onward to their own peers. Blocks are sent as short identifiers rather than full data where possible, to cut bandwidth and delay.
4 · Mining and Proof-of-Work
Transactions are bundled and sealed.
- The coinbase transaction
- The block's first transaction, written by the miner to pay themselves the block reward plus the fees inside.
- The block header
- Eighty bytes summarising the block: version, the previous block's fingerprint, a summary of every transaction in it, a timestamp, the target, and the nonce.
- The work itself
- Miners hunt for a nonce that makes the header's fingerprint fall at or below the target — the "starts with enough zeros" rule from earlier, stated precisely.
- Difficulty adjustment
- Re-tunes every 2,016 blocks, roughly two weeks, so blocks keep averaging ten minutes. It can move at most fourfold in either direction per period.
5 · Which history is the real one
What happens when two miners win at the same moment.
- Chaining
- A mined block is checked by other nodes and appended by referencing the previous block's fingerprint.
- The longest-chain rule
- If two miners win at once the chain briefly forks. The branch with the most accumulated work wins, and the other is dropped.
- Finality
- Transactions from a dropped block return to the mempool and are mined again. The more blocks pile on top of yours, the more exponentially expensive reversal becomes.
Words you will keep meeting
- Miner
A machine racing to guess fingerprints in exchange for the block reward.
- Node
Anyone running Bitcoin's software — verifies blocks and keeps a full copy of the chain.
- Hash
A digital fingerprint of some data. Change one bit of the data and the whole fingerprint changes.
- Confirmation
How many blocks sit on top of your transaction. More blocks, harder to undo.
Now watch it happen
The clock is these same numbers, live, on one screen.