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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 given above ...
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 ...
Devices may encompass multiple logical units, which are addressed by logical unit number (LUN). Simple devices have just one LUN, more complex devices may have multiple LUNs. A "direct access" (i.e. disk type) storage device consists of a number of logical blocks, addressed by Logical Block Address . A typical LBA equates to 512 bytes of storage.
On non-partitioned storage devices, such as floppy disks, the Boot Sector is the first sector (logical sector 0 with physical CHS address 0/0/1 or LBA address 0). For partitioned storage devices such as hard disks, the Boot Sector is the first sector of a partition, as specified in the partition table of the device.
[4] [5] It defines new functions within the INT 13h service, all having function numbers greater than 40h, that use 64-bit logical block addressing (LBA), which allows addressing up to 8 ZiB. (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).
The CHS addresses of a partition are hard to interpret without knowledge of the (virtual) disk geometry, because CHS to LBA translations are based on the number of heads and the number of sectors per track. However, the given LBA start address and the given partition size in sectors permit to calculate a disk geometry matching the given CHS ...
The term fixed-block architecture was created by IBM in 1979 [3] to distinguish this format from its variable-length record format. Each track is divided into fixed-length blocks, consisting of an ID field and a data field. Application programs refer to blocks by relative block number, and cannot address them by cylinder, head and record.