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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 ...
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 ...
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. The usage of LBAs has evolved over time and so four different command variants are provided for reading and writing data.
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 ...
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 number of address spaces available depends on the underlying address structure, which is usually limited by the computer architecture being used. Often an address space in a system with virtual memory corresponds to a highest level translation table, e.g., a segment table in IBM System/370.
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 ...
Usually, flash memory controllers also include the "flash translation layer" (FTL), a layer below the file system that maps host side or file system logical block addresses (LBAs) to the physical address of the flash memory (logical-to-physical mapping). The LBAs refer to sector numbers and to a mapping unit of 512 bytes.