A blockchain is an electronic & public ledger of all Bitcoin transactions that are executed till date. The blocks are added to the blockchain in a linear, chronological order. Each node (computer connected to the Bitcoin network using a client that performs the task of validating and relaying transactions) gets a copy of the blockchain, which gets downloaded automatically upon joining the Bitcoin network. The blockchain has complete information about the addresses and their balances right from the genesis block to the most recently completed block. Its continuously growing and its distributed database protects tampering and revision, even by operators of the data store's nodes.