1. For use with an address sequence produced from a computing system having a single level storage, a system for obtaining data for use in computing average access times for completing storage reference operations in a multi-level storage hierarchy, comprising emulation means for emulating each hierarchical level in said multi-level storage other than the main storage level by receiving said address sequence and recording the segments of storage located at each of said emulated levels, counting means connected to said emulation means to provide a record of hits and misses for fetch and store memory references from said address sequence at each of said emulation means, and address generation means connected between emulation means for adjacent levels for transferring a displaced segment of storage at a higher level to a lower level where said displaced segment is pushed out of said higher level by the need to record a segment received from said address sequence.