What are bad blocks?
First you need to understand a little about how disk storage works, and how data is organised on a typical hard disk. Disks are divided up into blocks; the arrangement of the blocks on the physical surface(s) of the disk doesn’t matter for the purposes of this discussion, but it is worth knowing that each block is in fact a particular sector on a particular track (a concentric ring of sectors at a particular distance from the disk hub) of a particular platter (a physical disk surface). Sometimes you may also see the term cylinder, which refers to a group of tracks, one on each surface of each platter, all at the same distance from the hub (if you visualise this in your mind, the tracks form a cylinder). In order to avoid giving bad data back to the user of a disk, each block, in addition to the space provided for data storage (usually 512 bytes per sector, though not always), there is a checksum of some description, often a cyclic redundancy check or CRC. Whenever the disk reads data f
