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TestDisk retrieves the LBA size and CHS geometry of attached data storage devices (i.e. hard disks, memory cards, USB flash drives, and virtual disk images) from the BIOS or the operating system. The geometry information is required for a successful recovery.
Negative LBA addresses indicate a position from the end of the volume, with −1 being the last addressable block. The GUID Partition Table ( GPT ) is a standard for the layout of partition tables of a physical computer storage device , such as a hard disk drive or solid-state drive , using universally unique identifiers (UUIDs), which are also ...
Logical block addressing (LBA) is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disk drives. LBA is a particularly simple linear addressing scheme; blocks are located by an integer index, with the first block being LBA 0, the second LBA 1 ...
Cylinder, head, and sector of a hard drive. Cylinder-head-sector (CHS) is an early method for giving addresses to each physical block of data on a hard disk drive.. It is a 3D-coordinate system made out of a vertical coordinate head, a horizontal (or radial) coordinate cylinder, and an angular coordinate sector.
(An ATA drive can also support 28-bit or 48-bit LBA which allows up to 128 GiB or 128 PiB respectively, assuming a 512-byte sector/block size). This is a "packet" interface, because it uses a pointer to a packet of information rather than the register based calling convention of the original INT 13h interface.
The usage of LBAs has evolved over time and so four different command variants are provided for reading and writing data. The Read(6) and Write(6) commands contain a 21-bit LBA address. The Read(10), Read(12), Read Long, Write(10), Write(12), and Write Long commands all contain a 32-bit LBA address plus various other parameter options.
Besides being an obvious indexing of disk blocks, LBA refers to specific ATA standards, and its interaction with the coexisting CHS systems. Besides the 10/8/6 CHS of INT 13H and the DOS MBR, the 16/4/8 CHS and 28-bit LBA of ATA-1, and the 48-bit LBA of ATA-6, there's a 32 bit LBA in the DOS MBR. There's a lot of history here.
Still later, magnetic hard disks employed an evolution of LBA where the size of the addressable disk sectors can differ from the physical block size. For example, Advanced Format (AF) 512e HDDs use 4096-byte physical sectors, while their firmware provides emulation for a virtual sector size of 512 bytes; thus, "512e" stands for "512-byte ...