What Is a Blockchain? The Shared Record Behind Crypto

A blockchain is a shared record of transactions, written in pages called blocks, where each new page carries a fingerprint of the one before it. Thousands of computers keep identical copies and compare them constantly. That chain of fingerprints is what makes the record hard to edit: change an old page and every page after it stops matching, in public, everywhere at once.

Why blocks and not just a list?

Picture a notebook that a whole town shares. Every ten minutes someone fills a page with the payments that happened, stamps it with a short code calculated from the previous page, and everybody copies the new page into their own notebook. Rub out a line from last Tuesday and your code no longer matches anyone else's, so your notebook is simply ignored. Bitcoin adds a page roughly every ten minutes, Ethereum about every twelve seconds, Solana several times a second - the rhythm differs, the idea does not.

Who decides what goes in a block?

Whoever earns the turn. On Bitcoin, computers race to solve a hard puzzle, and the winner writes the next block and is paid in new bitcoin for the trouble. On Ethereum, participants lock up coins as a deposit and are chosen in turn; cheat, and the deposit is taken away. Both methods make honest work the profitable option, which is why a network of strangers settles on the same history without a referee.

Can you look inside?

Yes, and that surprises people. Every block and every transaction is public. Sites called block explorers let you type an address or a transaction code and see the amount, the fee and the exact moment it was confirmed. You see addresses rather than names, so it is pseudonymous rather than anonymous - the activity is permanently visible to anyone who looks, which is worth remembering before you post your address in public.

The best way to make this concrete is to look up a real transaction in an explorer and watch the confirmations tick up as new blocks arrive. From there, what a block contains goes one level deeper, and how cryptocurrency works puts the whole picture together.