English: Graphic of data fields in Bitcoin block chain. Simplified depiction: some fields are missing.

• Prev_Hash: hash value of previous block. The purpose is to chain all blocks together.
• Tx_root: root hash value of a hash tree (w:merkle tree) over all transactions.
• Timestamp: creation time of block, as seen by block creator. The timestamp is checked by other clients and must be within a certain window (tolerates small clock skews).
• Nonce: any number to make sure the resulting hash value of this block is below the target hash value. The Nonce is a 32 bit number and the 2^32 number space is exhausted during mining within less than a second.

The transactions (Tx0, Tx1, ...) are appended to the block. The first transaction generates new bitcoins and contains the coinbase field which includes an extraNonce to provide a larger search space for valid block hash values.