Patent ID: 8984211
Filing Date: 2015-03-17
Classification: G06F,G11C,Y02D

Abstract:
1. A computer system, comprising: a storage system, which comprises a storage controller and one or more nonvolatile memory devices; and a management system coupled to the storage system, wherein the nonvolatile memory devices each comprise multiple memory cells, each memory cell having semiconductor characteristics enabling the storage of N-bits worth of data, and wherein the storage controller: stores storage configuration information indicating either a capacity or an address space of the nonvolatile memory device; stores cell mode information indicating a cell mode for stipulating the number of bits to be stored in the memory cells; receives a cell mode change request from the management system; and either increases or decreases an amount of data to be stored in the nonvolatile memory device subsequent to the request, by changing the cell mode information in accordance with the request and changing either the capacity or the address space of the storage configuration information wherein the memory cell is a flash memory cell for which a characteristic relating to data stored in the memory cell changes when the number of bits to be stored changes, wherein data storage in the memory cell is carried out by using cell programming to change a threshold voltage, which is a voltage applied to a control gate when a prescribed amount of electrical current begins to flow between a source gate and a drain gate, wherein in a first cell mode, a range between a minimum value and a maximum value of the threshold voltage is divided into sub-ranges of 2N and all the divided ranges are used to store N-bits worth of data in one memory cell, and wherein in a second cell mode, a first divided range including the minimum value and a second divided range not including the maximum value are used to store one-bit worth of data in one memory cell.