Block

A block is the fundamental building unit of any blockchain — think of it as a single page in an ever-growing digital ledger, permanently recording a batch of verified transactions along with metadata that connects it to the pages before and after it.

Every block typically contains several key pieces of information: a set of transactions that occurred during a given window of time, a timestamp marking when the block was created, a cryptographic hash uniquely identifying the block’s contents, and a reference to the hash of the previous block, which is what physically links blocks together into an unbroken chain.

This last piece, the reference to the previous block’s hash, is what gives blockchain its security and immutability. Because each block’s hash depends on the data inside it, and each new block references the previous block’s hash, altering any single transaction in a past block would change that block’s hash entirely, which would break the link to every subsequent block. To successfully falsify a transaction, an attacker would need to recompute every block that came after it, across a majority of the network, simultaneously — a practically impossible feat on any established blockchain.

On bitcoin, a new block is added roughly every 10 minutes, and blocks are typically considered fully confirmed after several additional blocks are added on top of them, since each additional confirmation makes reversing that block exponentially harder. For everyday users on Kurdcoin, understanding blocks helps explain why transactions require confirmations before being treated as final, and why blockchain data, once recorded, is considered essentially permanent.