PSEUDO-RANDOM CODE IMPLEMENTED VARIABLE BLOCK-SIZE STORAGE MAPPING DEVICE AND METHOD

A directory, or index, of variable-sized pages of data for use in a two-level storage system employing virtual addressing, wherein data is stored in a large capacity main storage and retrieved to a smaller, faster buffer storage for processing. If a desired piece of data indicated by a virtual address is not currently resident in buffer storage, the location of the beginning of the page containing that data in main storage is found by searching the directory. Directory addresses for searching the directory are formed by a pseudo-random function of two parameters, the virtual address and a count. Since a larger page-size entry will be addressed statistically more frequently than a smaller page-size entry, a new directory entry for a given page size is made in the first location along its algorithm chain which currently contains either an invalid entry or a smaller page-size entry. Thus, it may be necessary to relocate a smaller page-size entry further down its chain.