Bitcoin is not an app. It is not a company. It is not a file you copy. It is three things stuck together: a network of computers, a public ledger anyone can check, and a unit — bitcoin, often written BTC — whose protocol caps supply at 21 million.

On 31 October 2008 a text signed Satoshi Nakamoto appeared under the title *Bitcoin: A Peer-to-Peer Electronic Cash System*. On 3 January 2009 the first block was written. In that block, a line from the London *Times*: the chancellor on the brink of a second bank bailout. The context is not decoration. Bitcoin is born after a crisis in which some firms were too big to fail, and some accounts too small to matter.

A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution.— Satoshi Nakamoto, white paper, 31 October 2008

What it is

The ledger is called the blockchain. Each block chains the previous one. Once a transfer sits deep enough, changing it would mean redoing the computational work of everything that follows — in front of the rest of the network. Nobody needs a bank to know if a balance is true. A node, or several, and a comparison, are enough.

Three words get mixed. Bitcoin, capital B, is the system. bitcoin, lower case, is the unit. BTC is the ticker. One bitcoin splits into 100 million satoshis. You do not need a whole coin to use it.

The network has no headquarters. The rules live in the software, mainly Bitcoin Core, and in the agreement of the nodes that run it. A change does not enter by decree. It enters if enough people run it. That is slow. That is the point.

What it is not

It is not anonymous. Addresses are public strings. What you hide is the name — until an exchange, an invoice or an inquiry ties it. It is not magically unforgeable: security is the amount of honest compute, not a spell. It is not instant cheap payment on the base chain. A block aims at ten minutes. Fees rise when the queue grows. The Lightning Network exists for that: smaller, faster payments above the chain, not instead of it.

It is not a share. Holding bitcoin gives no vote in a company, and no dividend. The price moves because people trade it for dollars, euros, other crypto. Nothing in the protocol promises a price.

How a transaction leaves

You send to an address. To spend, you need the matching private key. The holder of the key signs. Nodes check the signature, the amount, and that those coins have not already been spent. Then the transaction waits in the queue — the mempool — until a miner puts it in a block.

Lose the key, lose the money. Give it away, give the money. There is no “forgot password” with a notary of the network. That is the most useful sentence, and the most ignored.

Who writes the blocks

Miners compete with computing power. The winner of a round proposes the next block. If it is valid, the network adds it. The miner receives the reward: new bitcoin, plus the fees of the transactions in the block. Since 20 April 2024 that creation reward is 3.125 BTC per block. It was 50 in 2009, then 25, 12.5, 6.25. Every 210,000 blocks — about four years — it is cut in half. That is the halving. The next one is due around block 1,050,000, in 2028, at 1.5625 BTC. The calendar is here.

Difficulty adjusts every two weeks so the pace stays near ten minutes, whether machines are more numerous or not. Hashrate — total network power — is not a straight line. It peaked in late 2025, then receded. In mid-September 2026 estimators put it around 940 to 990 exahash per second, depending on the window. Some halls now rent to artificial intelligence. That describes listed-company revenue, not a network that changed jobs. We cut that here.

Why 21 million

The cap is in the code. In mid-September 2026 a little more than 20.08 million bitcoin have already been created, about 95.6% of the maximum. The rest will come out more and more slowly, until around 2140. Some is lost: thrown keys, dead disks, addresses nobody remembers. Nobody publishes a solid census of that share. Saying “X million lost” without a method is folklore.

Scarcity does not make the price on its own. It only says you cannot print more for a budget. The rest is demand, liquidity, fear, flows.

What moves the price

Four forces return. New supply, which shrinks at each halving. Flows, notably the U.S. spot ETFs: money in, money out, the price often follows the pipe more than the story. Rates and the dollar, because bitcoin is still mostly traded in dollars. Accidents: an exchange that falls, a state that seizes, a whale that sells. Mt. Gox in 2014, FTX in 2022. The protocol kept going. Customers, not always.

In mid-September 2026 bitcoin trades around $77,000. That is not advice. It is a date. The 2025 high is not a law. A price can stay low for a long time. A price can break a high without “the cycle” owing it.

A country can adopt it as legal tender, like El Salvador. Another can tax it harder, like Germany at 25% from 2027. Neither rewrites the ledger.

How to hold some

Two families. With an intermediary: a platform that holds the account. It is simple. It is also trusting them with custody, withdrawals, survival. In Europe, MiCA covers some of these actors. That does not prevent an outage, a seizure, a mistake. At home: a wallet whose keys you hold. A dedicated device — Ledger, Trezor and others — keeps the key out of the browser. A bitcoin-only platform can help you buy without leaving everything on deposit. The recovery phrase is written offline. It is not photographed. It is not pasted into an email.

Scams do not need to hack the network. They need you to give the key, click fake support, send “to unlock a withdrawal”. The protocol does not refund.

Where the network stands in 2026

The chain runs. Blocks come out. Median fees often sit in dollar cents, outside congestion. Lightning exists, imperfect, used. Neighbouring layers — Liquid, others — promise more speed, at the cost of other trust assumptions. They are not Bitcoin. They are neighbourhoods.

What the network holds: a public history, a predictable issuance, the absence of a central switch. What it does not hold: a price, magical anonymity, immunity from human error, immunity from the laws of the country you live in. The quantum computer is a file, not a published countdown. We kept it away from folklore. Ledger’s Charles Guillemet puts it another way: the risk is in the schemes, not in a film.

Bitcoin is a tool. You can ignore it. You can hold it badly. You can talk about it as a religion. The ledger does not listen. It lines up blocks.