The Blockchain data structure is an ordered, back-linked list of blocks of transactions. The blockchain can be stored as a flat file, or in a simple database. Blocks are linked “back,” each referring to the previous block in the chain. The blockchain is often visualized as a vertical stack, with blocks layered on top of each other and the first block serving as the foundation of the stack. The visualization of blocks stacked on top of each other results in the use of terms such as “height” to refer to the distance from the first block, and “top” or “tip” to refer to the most recently added block.
Blockchain: The green boxes are the blocks and the arrows show how they confirm each other.
Each block within the blockchain is identified by a hash, generated using the SHA256 cryptographic hash algorithm on the header of the block. Each block also references a previous block, known as the parent block, through the “previous block hash” field in the block header. In other words, each block contains the hash of its parent inside its own header. The sequence of hashes linking each block to its parent creates a chain going back all the way to the first block ever created, known as the genesis block.
For a deep dive into the fundamentals of blockchain, check out the talk given by Dr. Marcelo Salhab Brogliato - CTO & co-founder of Hathor Labs.