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Before broadcasting block into bitcoin blockchain, Does a Block transactions are included in a block or only the hash of them are included in a block. While I am surfing through net, I came across two images which are very ambiguity because in picture-1 transactions are out of block and in picture-2 transactions are included in block and the images are as shown below:

Picture -1: 1

Picture -2

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in picture-1 transactions are out of block and in picture-2 transactions are included in block

In your picture-1, the transactions are NOT shown as outside the block. They are shown as outside the "block header"

Your picture-1 has the caption "Simplified Bitcoin Block Chain". You should take care not to interpret a simplified diagram as if it were completely accurate. The second diagram is also simplified and not a complete specification of data in a block.

Both these diagrams have misleading elements. For example the direction of arrows in the first diagram. The inclusion of "proof of work" in the second diagram as if that were a data item stored in the block structure. It isn't.


Are transactions included in a block or is only the Merkle-root hash included in a block

The cause of this confusion is that

  • The block hash includes the block header only†.
  • The block data includes a block-header and all transaction data.

†The hash of the block does not directly include the transaction data. The transaction data is included indirectly.

One of the items in the block header is the Merkle root. The Merkle root is a hash resulting from repeated pairwise hashing of transaction data. A consequence of this is that altering any transaction would result in a different block hash.


See

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  • I believe the field "proof of work" referred to is actually the nonce; that is sometimes referred to as the proof. Jul 17, 2022 at 12:30
  • @Pieter: In Picture-2, "proof of work" is pointed to by "previous block" in the next block and it starts with many zeroes. Aren't both rather suggestive of block hash? Jul 17, 2022 at 21:07
  • Oh, yes, I guess that's an attempt at referring to the block hash. Strange that it's not hexadecimal though. Jul 17, 2022 at 22:24
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Merkle tree root exists and is stored inside Block header.

Transactions are themselves the leafs of the merkle tree.

The merkle tree is used to attach Transactions to the Block header.

Therefore, in Bitcoin, Block is Block header and Transactions

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