Bad blocks are blocks that contain one or more invalid bits whose reliability is not guaranteed. Bad blocks may be present when the device is shipped, or may develop during the lifetime of the device. Devices with bad blocks have the same quality level and the same AC and DC characteristics as devices where all the blocks are valid. A bad block does not affect the performance of valid blocks because it is isolated from the bit line and common source line by a select transistor. Bad block management, block replacement and the error correction code software are necessary to manage the error bits in NAND flash devices. The application note covers all Numonyx NAND flash memories. Refer to the relative datasheets for the full list of root part numbers and for further information on the devices.