Foundations of Blockchain

Block structure

The data structure of a Bitcoin block holds a collection of transactions and metadata information about the block. A block is made up of a header and body, which consists of all the transactions. A block holds more than 500 transactions, on average.

Table 5.2 shows all the fields that are included in a block. The dominant part of the block is the header and transactions, which would occupy variable size. Each field shows the size or the transactions occupied in the block:

Field	Description	Size
Magic no	The value is always 0xD9B4BEF9	4 bytes
Block Size	Number of bytes up to the end of the block	4 bytes
Block Header	Consists of six items	80 bytes
Transaction Counter	Integer count	1 - ...