reference fingerprint

At step 420, a read operation is performed for the selected memory cells. At step 430, data from each of the selected cells which was read in the read operation of step 420 is verified to have the same or a different logical value than the logical value written in step 350. By way of example, where the data contained at the selected cell is assigned the level of trapped charges indicated by the threshold, and a value representing the assigned level of trapped charges is stored for each cell. A cell which contains a logical “1” but which was read as a logical “0” in the read operation of step 420 or a cell which contains a logical “0” but which was read as a logical “1” in the read operation of step 420. At step 440, each of the cells having a variation (e.g., which was written as a “0” and recognized as a “1”, and which was written as a “1” and recognized as a “0”) is removed from the list of selected memory cells. At step 450, the list of selected cells is examined to determine if it is empty. If the list is not empty, the process proceeds to step 420. If the list is empty, the process proceeds to step 460. At step 460, the stored representations of the error map for the selected cells are assembled to create a reference fingerprint which can be used to identify the memory array.

The reference fingerprint is then stored in the device which is accessing the memory array. By way of example, the reference fingerprint can be stored in hard drive 190 of the system 100 of FIG. 1, and the memory array could be the memory 185 ofFIG. 1. Thus, in subsequent uses of the memory array whose reference fingerprint is determined, the identity of the memory array can be verified by the device using the reference fingerprint even where the memory array has been detached from the device. Where the identity is verified, it is determined that the data on the memory array is not a duplicate or from a counterfeit card which contains information duplicated from a legitimate card having the reference fingerprint.