In a b-tree, is it faster if all nodes are near by memory location?

or its the same as we are getting it from RAM anyways.

Had another question, when the Btree is not in use. can we store it in file system? is partial storage possible? like the root and top level nodes are in RAM, some branches unused are in file system.

Question: In a b-tree, is it faster if all nodes are near by memory location?