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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
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.
The IBM System/38, and the IBM AS/400 in its CISC variants, use 48-bit addresses. 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.
INT 13h is shorthand for BIOS interrupt call 13 hex, the 20th interrupt vector in an x86-based (IBM PC-descended) computer system.The BIOS typically sets up a real mode interrupt handler at this vector that provides sector-based hard disk and floppy disk read and write services using cylinder-head-sector (CHS) addressing.
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.
On the 360/65, 360/67 and every successor prior to z/Architecture, it logically swaps a 4096 byte block of storage with another block assigned to the CPU. On z/Architecture, [3] prefixing operates on 8196-byte blocks. IBM classifies addresses on these systems as: [4] Virtual addresses: addresses subject to dynamic address translation
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve stored data, each datum must have an address where it can be located.
The physical address of computer memory banks may be mapped to different logical addresses for various purposes. In a system supporting virtual memory, there may actually not be any physical memory mapped to a logical address until an access is attempted. The access triggers special functions of the operating system which reprogram the MMU to ...