Information storage systems and information storage device

PROBLEM TO BE SOLVED: To guarantee accuracy of overlapping determination with a small computing amount.SOLUTION: An information storage system comprises a host device and an information storage device. The information storage device comprises a compression section, a storage section and a first interface section. The compression section compresses data input from the host device. The storage section stores compressed data indicating data compressed by the compression section. The first interface section transmits second writing data obtained by compressing first writing data by the compression section to the host device when the first writing data are input from the host device, and transmits read-out compressed data indicating compressed data read-out from the storage section on the basis of address information to the host device when the address information corresponding to the first writing data are input from the host device. The host device comprises a determination section determining the first writing data to be already stored when the second writing data coincide with the read-out compressed data.SELECTED DRAWING: Figure 1