What are the differences between B trees and B+ trees?

Question

In a b-tree you can store both keys and data in the internal and leaf nodes, but in a b+ tree you have to store the data in the

Answer 1

One possible use of B+ trees is that it is suitable for situations where the tree grows so large that it does not fit into available memory. Thus, you'd generally expect to be doing multiple I/O's.
It does often happen that a B+ tree is used even when it in fact fits into memory, and then your cache manager might keep it there permanently. But this is a special case, not the general one, and caching policy is a separate from B+ tree maintenance as such.

Also, in a B+ tree, the leaf pages are linked together in a linked list (or doubly-linked list), which optimizes traversals (for range searches, sorting, etc.). So the number of pointers is a function of the specific algorithm that is used.