Bitcoin is a digital currency that runs on a network of computers instead of a bank
Bitcoin exists only as data on computers around the world. When you own bitcoin, you own a private key — a long string of characters that proves you control a certain amount of bitcoin. To send bitcoin to someone else, you use your private key to sign a transaction, and the network records that transfer. No bank, government, or company sits in the middle. The network itself verifies that the transaction is real and that you actually own what you are sending.
This is different from money in your bank account, where the bank keeps the ledger and decides whether a transaction goes through. With bitcoin, thousands of computers called nodes each keep a copy of the entire transaction history. When you send bitcoin, these nodes check that your transaction is valid before adding it to the record.
Key Takeaways
- Bitcoin transactions are verified by a network of computers rather than a central authority like a bank.
- Your private key is the password that proves you own your bitcoin and allows you to send it.
- Transactions are grouped into blocks and added to a chain of previous blocks, which is why the technology is called blockchain.
- Miners compete to solve math problems that verify transactions and add new blocks, and they receive newly created bitcoin as a reward.
- The bitcoin network is designed so that only 21 million bitcoin will ever exist, and new coins are created at a predictable, slowing rate.
How your private key and public address work together
Your private key is a secret number that only you know. You never share it with anyone. Your public address is derived from your private key through math, but you cannot work backwards from the public address to find the private key. Think of it like a mailbox: your public address is the mailbox number that anyone can see and use to send you mail, but your private key is the only key that opens it.
When you want to receive bitcoin, you give someone your public address. They send bitcoin to that address, and it appears in your wallet. When you want to send bitcoin, you use your private key to sign the transaction, proving that you authorized it. The network then verifies your signature using your public address, confirming that the bitcoin really belongs to you.
If someone gets your private key, they can send all your bitcoin away. If you lose your private key, you lose access to your bitcoin forever — there is no customer service to call and no way to recover it.
What a blockchain is and why it matters
A blockchain is a record of all bitcoin transactions arranged in blocks. Each block contains a list of transactions, a timestamp, and a reference to the previous block. This chain of blocks goes all the way back to the first bitcoin transaction in 2009. Because each block references the one before it, changing an old transaction would break the chain, and the network would reject it.
Every node on the network keeps a full copy of the blockchain. This means no single person or company controls the record. If someone tried to fake a transaction or change the past, the thousands of other copies would contradict them. The network would ignore the fake version.
The blockchain is public, so anyone can look up any transaction that has ever happened. You can see the amount, the addresses involved, and the time it occurred. However, addresses are just long strings of characters, so you cannot tell who owns an address just by looking at it unless they tell you.
How miners verify transactions and create new bitcoin
Miners are computers that collect pending transactions and compete to add them to the blockchain. To do this, they must solve a difficult math problem. The first miner to solve it gets to add a new block of transactions to the chain. As a reward, that miner receives newly created bitcoin plus the transaction fees from all the transactions in that block.
This process is called proof of work. The math problem is hard to solve but straightforward to verify. Once a miner solves it and adds a block, all the other nodes quickly check that the solution is correct. If it is, they add that block to their copy of the blockchain. If it is not, they reject it and keep working on their own block.
The difficulty of the math problem adjusts automatically so that a new block is added roughly every 10 minutes, no matter how many miners are working. When more miners join the network, the problem gets harder. When miners leave, it gets easier. This keeps the rate of new blocks steady.
Why bitcoin supply is limited to 21 million coins
Bitcoin's code was written so that only 21 million bitcoin will ever be created. This is different from regular money, which governments can print as much of as they want. The first bitcoin miners received 50 bitcoin per block. Every four years, this reward is cut in half. It started at 50, then dropped to 25, then 12.5, then 6.25, and will continue halving until the reward becomes so small it rounds to zero.
At that point, no new bitcoin will be created, but miners will still verify transactions in exchange for transaction fees. Because the supply is fixed and cannot be increased, some people see bitcoin as a store of value similar to gold. Others argue that a fixed supply makes it unsuitable as everyday money.
The next halving event occurs at a predictable block height, not at a predictable date, because block timing varies slightly. You can calculate roughly when it will happen based on the current block height and the 10-minute average, but the exact date depends on mining activity.
How long transactions take and why they sometimes get stuck
When you send bitcoin, your transaction enters a mempool — a waiting area where pending transactions sit until a miner includes them in a block. If the network is busy, your transaction might wait hours or even days. If the network is quiet, it might be included in the next block, which takes about 10 minutes.
You can pay a higher transaction fee to encourage miners to include your transaction sooner. Miners prioritize transactions with higher fees because they earn more from them. If you pay a very low fee during a busy time, your transaction might get stuck and eventually be dropped from the mempool without being processed.
Once a miner includes your transaction in a block, it is considered confirmed. Most exchanges and services wait for multiple confirmations — usually six blocks, which takes about an hour — before treating the transaction as final. This protects against the rare possibility that the block gets rejected and the transaction needs to be redone.
What happens if the network disagrees about the blockchain
Occasionally, two miners solve the math problem at nearly the same time, and the network temporarily splits. Some nodes receive one block first, others receive a different block first. The network follows the rule that the longest chain is the true one, so miners keep working on whichever chain they received first. Eventually, one chain grows longer than the other, and the network reunites around it. Transactions in the shorter chain are returned to the mempool and may be included in future blocks.
This is called a fork, and it happens by accident roughly once per week. It is not a problem because the network automatically resolves it within minutes. However, this is why waiting for multiple confirmations matters — if you receive bitcoin and then the block containing your transaction gets orphaned, the transaction is undone.
A deliberate fork can also happen when developers change the rules of the network. If some nodes update their software and others do not, they may end up following different versions of bitcoin with different rules. This is how Bitcoin Cash and other alternative cryptocurrencies were created.
Frequently Asked Questions
Can bitcoin transactions be reversed?
No. Once a transaction is confirmed by the network, it cannot be reversed or canceled. If you send bitcoin to the wrong address by mistake, it is gone. This is why it is important to double-check addresses before sending. Some services offer insurance or recovery options, but the bitcoin protocol itself has no undo button.
Why does bitcoin use so much electricity?
Bitcoin mining requires solving difficult math problems, which takes computational power. Thousands of miners around the world are competing to solve these problems simultaneously, and only one wins per block. All the computing power used by the losers is wasted in that round. This is by design — the difficulty and energy cost make it expensive to attack the network or fake transactions.
What is the difference between bitcoin and blockchain?
Bitcoin is a specific cryptocurrency that runs on blockchain technology. Blockchain is the underlying technology — a way of recording transactions in a chain of blocks verified by a network. Many other cryptocurrencies and projects use blockchain, but they are not bitcoin. Bitcoin is one process of blockchain.
Can the government shut down bitcoin?
Because bitcoin runs on thousands of computers worldwide and has no central authority, a single government cannot shut it down. However, governments can make it illegal to buy, sell, or use bitcoin within their borders, and they can pressure internet service providers and banks to block access. Some countries have done this. Bitcoin would continue to exist and function, but it would be harder for people in those countries to participate.
How do I know my bitcoin is find?
Bitcoin is find if your private key is find. If you store your private key on a computer connected to the internet, hackers can potentially steal it. If you write it down and store it in a safe place, or use a hardware wallet designed to keep keys offline, your bitcoin is much harder to steal. The bitcoin network itself is find because changing past transactions would require redoing all the math work faster than the rest of the network, which is practically impossible.