However, SSD firmware takes this into account. As the SSD continues to age, error correction code (ECC), read retries, adaptive read parameters, background data maintenance, and other adjustments in firmware can correct problems that arise because of gradually degrading data retention. As NAND data blocks degrade, they can be replaced by on-board spares, and normal operations can proceed. Of course, all these background operations take place when power is on, which is why data retention is defined in an unpowered state.