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In logical block addressing, only one number is used to address data, and each linear base address describes a single block. The LBA scheme replaces earlier schemes which exposed the physical details of the storage device to the software of the operating system. Chief among these was the cylinder-head-sector (CHS) scheme, where blocks were addressed by means
where A is the LBA address, N heads is the number of heads on the disk, N sectors is the maximum number of sectors per track, and (c, h, s) is the CHS address. A Logical Sector Number formula in the ECMA -107 [ 3 ] and ISO / IEC 9293:1994 [ 15 ] (superseding ISO 9293:1987 [ 16 ] ) standards for FAT file systems matches exactly the LBA formula ...
From RAMAC until the early 1960s most hard disk drive data were addressed in the form of a three number block addressing scheme Cylinder, Head & Sector (CHS); the cylinder number, which positioned the head access mechanism; the head number, which selected the read-write head; and the sector number, which specified the rotational position of a ...
The partition type (or partition ID) in a partition's entry in the partition table inside a master boot record (MBR) is a byte value intended to specify the file system the partition contains or to flag special access methods used to access these partitions (e.g. special CHS mappings, LBA access, logical mapped geometries, special driver access, hidden partitions, secured or encrypted file ...
Like MBR, GPT uses logical block addressing (LBA) in place of the historical cylinder-head-sector (CHS) addressing. The protective MBR is stored at LBA 0, and the GPT header is in LBA 1, with a backup GPT header stored at the final LBA. The GPT header has a pointer to the partition table (Partition Entry Array), which is typically at LBA 2 ...
The partition type of an extended partition is 0x05 (CHS addressing) or 0x0F (LBA addressing). [4] DR DOS 6.0 and higher support secured extended partitions using 0xC5 , which are invisible to other operating systems.
Prior to 1995, versions of DOS accessed the disk via CHS addressing only. When Windows 95 (MS-DOS 7.0) introduced LBA disk access, partitions could start being physically located outside the first c. 8 GB of this disk and thereby out of the reach of the traditional CHS addressing scheme.
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.