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Why blockchain exists at all
A regular database lives on a company's server. Your bank keeps records of your money, and you take the bank's word for it: the numbers on your screen are entries in its database. It can freeze them at will; it can lose them by mistake.
Blockchain solves the same problem — keeping records of who owns how much — without a single database owner. Thousands of independent computers (nodes) around the world store the same copy of the records and constantly cross-check it. Forging an entry in such a system is nearly impossible: you would have to fool the majority of the network at once.
How blocks are built
Transfer records are collected in batches — blocks. Every new block contains:
- a list of transactions (who, to whom, how much);
- a reference to the previous block — a cryptographic fingerprint (hash).
That reference chains blocks together — hence the name. Changing an old transaction means changing a block, which changes its hash, which breaks every block after it. The network spots the forgery instantly and rejects it.
You can look at a blockchain with your own eyes: every transaction and every block is public. For Ethereum — etherscan.io, for Solana — solscan.io. We'll learn to use them in lesson 3.
Who adds the blocks
New blocks are added by validators (miners, in older networks). The network pays them a reward for honest work and punishes attempts to cheat. The economics are designed so that playing fair pays better than attacking.
This gives blockchain its key property: nobody can cancel your transaction, freeze your wallet, or roll the network back. Not a company, not a state, not the network's creators. In exchange, all responsibility for your funds is yours. We'll dig into that in the wallets module.
Key takeaways
- A blockchain is a shared record base with no single owner; thousands of independent nodes keep copies.
- Records are packed into blocks chained by hashes — the past cannot be rewritten.
- Validators add blocks for rewards; honesty is enforced by economics, not trust.
- Freedom from intermediaries = full personal responsibility for your funds.