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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
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.
The layout of a disk with the GUID Partition Table. In this example, each logical block is 512 bytes in size and each entry has 128 bytes. The corresponding partition entries are assumed to be located in LBA 2–33. Negative LBA addresses indicate a position from the end of the volume, with −1 being the last addressable block.
[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 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.
Some large / 8 blocks of IPv4 addresses, the former Class A network blocks, are assigned in whole to single organizations or related groups of organizations, either by the Internet Corporation for Assigned Names and Numbers (ICANN), through the Internet Assigned Numbers Authority (IANA), or a regional Internet registry.
When the 2321 data cell was discontinued in January 1975, [5] the addressing scheme and the device itself was referred to as CHR or CTR for cylinder-track-record, as the bin number was always 0. IBM refers to the data records programmers work with as logical records, and the format on DASD [a] as blocks or physical records.
The address size used in logical block addressing was increased to 48 bits with the introduction of ATA-6. The Ext4 file system physically limits the file block count to 48 bits. The minimal implementation of the x86-64 architecture provides 48-bit addressing encoded into 64 bits; future versions of the architecture can expand this without ...