On January 12, 2009, Satoshi Nakamoto sent Hal Finney 10 bitcoin as a test. That payment still sits in block 170 of the Bitcoin blockchain, and anyone can look it up today. Bitcoin works by keeping one shared ledger that every full node holds a copy of, adding a new block to it about every ten minutes, and letting coins move only when their owner signs with a private key.
Every moving part of the system shows up in that one payment, so I am going to explain Bitcoin by taking it apart.
How does Bitcoin work in simple terms?
Four pieces. That is all a beginner needs.
- A ledger. One public record of which coins sit at which addresses. Nobody owns it.
- Keys. A private key is the secret that lets you spend. Your wallet keeps it and uses it to sign payments.
- Nodes. Computers running Bitcoin software that each keep a full copy of the ledger and check every payment against the rules.
- Miners. The computers that put waiting payments in order, in blocks, and get paid in new coins and fees for doing it.
Here is how those four pieces moved the first payment from Satoshi’s wallet into the permanent record.
The first payment, taken apart
Satoshi did not have a balance of 50 bitcoin the way you have a balance in a checking account. He had one specific chunk of 50 bitcoin, created three days earlier as the reward for block 9. To pay Hal, his wallet spent that whole chunk and split it into new pieces.
| Part of the transaction | Amount | Where it went |
|---|---|---|
| Input | 50 BTC | The block 9 reward, January 9, 2009 |
| Output 1 | 10 BTC | Hal Finney |
| Output 2 | 40 BTC | Back to Satoshi, as change |
| Fee | 0 BTC | Nothing left over for the miner |
Fifty in, fifty out.
That is the first thing I would want a beginner to see. Bitcoin does not edit balances. It consumes old pieces of coin and creates new ones, and the rule every node checks is that the new pieces never add up to more than the old one. Whatever is left over goes to the miner as a fee. Satoshi left nothing over, and block 170 held only two transactions, so it did not matter. Today it does: block space is limited, and miners fill it with the payments that pay them most.
Who checked that Satoshi was allowed to send it?
Nobody’s permission was involved. The 50 bitcoin from block 9 were locked to a public key, and the only way to unlock them was a digital signature made with the matching private key. Every node that received the payment ran the same two checks: is the signature valid, and has this chunk of coin already been spent somewhere else?
The second check is the hard one. A digital file can be copied, so what stops someone from sending the same coins to two people at once? Satoshi named it as the problem the whole system exists to solve.
We propose a solution to the double-spending problem using a peer-to-peer network.
Satoshi Nakamoto, Bitcoin whitepaper, 2008
Signatures prove who may spend. They cannot, on their own, settle which of two conflicting payments came first. That job belongs to the miners.
Mining decides the order, and the order is the money
Valid payments wait in each node’s pool of unconfirmed transactions. A miner gathers a batch of them into a candidate block and then grinds through guesses until the block’s fingerprint, its hash, comes out below a target number. That search is the proof of work. It costs real electricity, and the first miner to find a valid answer broadcasts the block. The other nodes check it and add it to their copy of the chain.
Bitcoin Core’s own consensus code sets the pace. It targets one block every 10 minutes and resets the difficulty every 2,016 blocks, roughly every two weeks, so that the pace holds whether more or fewer machines are mining.
Here is why the order matters so much. Each block contains the fingerprint of the block before it. To rewrite block 170 today, an attacker would have to redo its proof of work and the work of every block stacked on top of it since 2009, faster than the rest of the network keeps adding new ones. The record is safe because changing it costs more than anyone can spend.
Mining is also where new coins come from. The 50 bitcoin Satoshi spent were the reward for block 9. That reward halves every 210,000 blocks, which is why the total supply stops just short of 21 million.
What is Bitcoin, and how does it work without a bank?
Compare it with a card payment. When you tap a card, your bank’s ledger and the merchant’s bank’s ledger change, and the banks decide whether the payment goes through. They can also reverse it later.
Bitcoin replaces the bank’s approval with checks anyone can run. The whitepaper put it plainly: an electronic payment system “based on cryptographic proof instead of trust.” Hal Finney did not need to trust Satoshi, or any company, to know the 10 bitcoin were his. He could verify it on his own machine. In my view that is the whole point of the design, and the rest is engineering in service of it.
The fair objection: it is slow on purpose
The strongest criticism of this design is the efficiency objection, and it is correct on its own terms. Every node re-checks every payment. Blocks are capped at 4 million weight units by the SegWit upgrade (BIP 141). A new block arrives about every ten minutes, not every second. A database run by one company would be far faster and far cheaper per payment.
I agree with all of that. As a payment database, Bitcoin is worse.
The trade is speed for having no one in charge. A ledger that one company runs is a ledger that one company can freeze, reverse, or inflate. Bitcoin gives up throughput so that nobody can. Whether that trade is worth it depends on whether you ever need it, which is a monetary question, not a technical one.
What you actually own
Your coins never sit inside your wallet. They are entries on the shared ledger, locked to keys. The wallet holds the keys.
That has two consequences a beginner should know before buying anything. Lose the private key, and no one can restore the coins, because there is no one to ask. Leave the coins on an exchange, and the exchange holds the key, so what you own is the exchange’s promise to give them back.
This guide stops at the mechanics. It does not tell you what Bitcoin is worth, and the same design that protects the record leaves the price free to fall a long way. The open questions for a beginner are about keys, fees, and custody, and those get their own pieces in this track.
Where this fits
- One rung down: What Is Bitcoin? (For Kids) explains the same idea for a younger reader.
- Same rung: What 21 Million Looks Like shows the supply cap that the block reward builds toward.
- One rung up: Bitcoin Halving Cycle Returns: Why Each Cycle Pays Less takes the halving into market history, in Advanced Bitcoin.
- Before Bitcoin: What Is Money? sets out the tests any money has to pass.
For further reading, the Bitcoin 101 shelf of the Card Catalog starts with Saifedean Ammous’s The Bitcoin Standard. That book link is an Amazon affiliate link; Modern Wealth Model may earn a commission at no cost to you.
Sources
- Satoshi Nakamoto, Bitcoin: A Peer-to-Peer Electronic Cash System, 2008.
- Transaction f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16, block 170, January 12, 2009 (UTC).
- Block 9 reward, transaction 0437cd7f8525ceed2324359c2d0ba26006d92d856a9c20fa0241106ee5a597c9, block 9, January 9, 2009 (UTC).
- Hal Finney, “Bitcoin and me”, BitcoinTalk, March 19, 2013.
- Bitcoin Core, chainparams.cpp (10-minute block target, two-week retarget, 210,000-block halving interval).
- BIP 141: Segregated Witness (4 million weight unit block limit).