B-tree is optimized for systems that read and write large blocks of data. B-b tree deletion example pdf are a good example of a data structure for external memory.
When data is inserted or removed from a node, its number of child nodes changes. In order to maintain the pre-defined range, internal nodes may be joined or split. Because a range of child nodes is permitted, B-trees do not need re-balancing as frequently as other self-balancing search trees, but may waste some space, since nodes are not entirely full. The lower and upper bounds on the number of child nodes are typically fixed for a particular implementation.
2 or 3 child nodes. In practice, the keys take up the most space in a node. The factor of 2 will guarantee that nodes can be split or combined. Each split node has the required minimum number of keys. A B-tree is kept balanced by requiring that all leaf nodes be at the same depth.