Chapter · Master Bitcoin
Blocks and the chain
Bitcoin transactions are bundled together into blocks, and each block links to the one before it, forming a chain. That is why it is called a blockchain. Once a transaction is buried under later blocks, rewriting it would mean redoing all of that work, which is effectively impossible. On average a new block is added about every ten minutes, and each one is broadcast to the whole network.
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What you get asked
Why is it called a blockchain?
Blocks of transactions are linked in order, each pointing back to the previous one. That linked structure is the chain in blockchain.
About how many minutes pass between new Bitcoin blocks on average?
The network targets one block roughly every ten minutes. It is an average, so some blocks arrive faster and some slower.
Waiting for more blocks to be added on top of your payment gives it more ___.
Each new block on top counts as one more confirmation. More confirmations make a transaction harder to reverse, so big payments often wait for several.
Order what happens when you send Bitcoin
A payment is signed, shared with the network, picked up by a miner, and then locked in more firmly as later blocks pile on.
Why is an old transaction very hard to reverse?
Every block builds on the ones before it. Changing an old block would force an attacker to redo all the work stacked above it, which is not realistic.
The rest of this chapter
Learn what Bitcoin is, how it works, and how ordinary people buy, hold, and secure it safely.