Semiconductor disc storage

Abstract

A semiconductor storage device is connected to at least one magnetic storage device. The input and output of data is made between the semiconductor storage device and an information processing device. The semiconductor storage device includes an electrically erasable non-volatile semiconductor memory which stores directory information of data stored in the magnetic storage device, a volatile semiconductor memory which has a storage capacity smaller than that of the non-volatile semiconductor memory and the storage contents of which are updated to store a part of the directory information having a higher frequency of access from the information processing device, and a CPU connected to the volatile semiconductor memory and the non-volatile semiconductor memory for making access to the volatile semiconductor memory and the non-volatile semiconductor memory in accordance with an access request from the information processing device, wherein when access to the volatile semiconductor memory made for access from the information processing device to the magnetic storage device hits on the part of the directory information, the CPU transfers the part of the directory information to the information processing device without making access to the non-volatile semiconductor memory and the information processing device makes access to the magnetic storage device on the basis of the part of the directory information When a failure is generated in the non-volatile semiconductor memory or when a predicted service life of the non-volatile semiconductor memory is elapsed, the non-volatile semiconductor memory is substituted by an alternate memory.