Paged Binary Trees
AVL trees tackle the problem of keeping an index in sorted order cheaply. They do not address the problem regarding the fact that Binary Searching requires too many seeks.
Paged Binary trees addresses this problem by locating multiple binary nodes on the same disk page.
In a paged system, you do not incur the cost of a disk seek just to get a few bytes. Instead, once you have taken the time to seek to an area of the disk, you read in an entire page from the file.
When searching a Binary Tree, the number of seeks necessary is log2(N+1). It is logk+1(N+1) in the paged version.