HPA
also: Host Protected Area
HPA (Host Protected Area) is a reserved section of a hard drive that is hidden from the operating system and ordinary disk tools, typically used by manufacturers for recovery partitions or firmware storage.
The Host Protected Area is a feature defined in the ATA/SATA specification that allows disk manufacturers to reserve a portion of drive capacity that remains inaccessible to standard operating systems and disk utilities. This hidden area exists below the normal addressable range reported to the OS.
Manufacturers commonly use the HPA to store recovery images, diagnostic tools, or firmware updates that persist even if the main operating system is wiped or corrupted. For example, many laptop vendors store a factory recovery partition in the HPA that users can access via a special key combination during boot.
The HPA can be modified or removed using specialized tools like hdparm with the --read-sector-count and --set-sector-count options, though this requires root access and caution—improper manipulation can make recovery data inaccessible.