hierarchical storage management

In computing, the organization of data storage so that information which is used most often is stored using the fastest access technology, and information used less often is stored on slower and less expensive storage devices.

For example, information that is accessed regularly will be kept in the main memory (fast, but expensive). Information that is required a little less often will be stored on hard disk (slower than memory, but less expensive), and information that is needed only occasionally is stored on optical devices or magnetic tape (very slow access time, but low in cost).