History of File StructuresV. Hash Tables
Retrieving entries in 3 or 4 accesses is good, but it does not reach the goal of accessing data with a single request.
From early on, Hashing was a good way to reach this goal with files that do not change size greatly over time.
Recently, Extendible Dynamic Hashing guarantees one or at most two disk accesses no matter how big a file becomes.