Old hard drives in ancient times (MFM days) had block defect tables (or defect list) - you never or rarely got a hard drive with 100% good sectors, and the addr

Old hard drives in ancient times (MFM days) had block defect tables (or defect list) - you never or rarely got a hard drive with 100% good sectors, and the addresses of the bad ones would literally be printed upon a sticker on the drive. This got moved inside the drive as part of "adaptives" - a list of bad blocks from manufacturing probably lives in some EEPROM or NAND in the modern drives. SSDs and microcontroller-based storage like SD cards and USB flash drives are the same - they certainly have some sort of defect list somewhere - I read somewhere that raw NAND is actually more expensive per GB than the same in an SD card because the SD card can have NAND with defects, but hide them through overprovisioning. What I'm saying is that CPU microcode isn't really a ROM in the sense of containing executable code, it's simply some data-like structure the device literally uses to work properly, like however modern drives do their adaptvies--but not executable code. Another example: Old arcade machines had small PROMs that held nothing but color table values for the display hardware (Pac-Man IIRC). Another example of something that's a ROM but probably not "firmware".