In a nonvolatile memory, that includes cells organized in a plurality of bit lines and a plurality of word lines, user data are stored in respective portions of each of two of the word lines. Control information is stored in a cell that is common to one of the bit lines and one of the two word lines. A cell that is common to the bit line and the other word line is used as a reference cell. A flash memory, that includes a plurality of primary cells and a plurality of spare cells, is interrogated to determine which spare cells have been used to replace respective primary cells. At least some of the other spare cells are used as reference cells.