Physical Disks
The OS must deal with the mess of physical devices:
- errors
- bad blocks
- missed seeks
The job of the OS is to hide this mess from higher levels by:
- providing low-level device control
- providing higher-level abstractions: files, database, ....
The OS may provide different levels of disk access
- physical disk block (surface, cylinder, sector)
- disk logical block (disk block #)
- file logical (file block, record, or byte #)