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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-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. Head selects a circular surface: a platter in the disk (and one of its two ...
A later development in disk addressing was logical block addressing , in which the cylinder-head-sector triplet was replaced by a single number, called the block number. Within the disk drive, this linear block number was translated into a cylinder number, head number and sector number.
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.
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 ...
However, with the introduction of virtual memory most application programs do not deal directly with physical addresses. Instead, they use logical or virtual addresses, which are translated to physical addresses by the computer's memory management unit (MMU) and the operating system's memory mapping mechanisms.
Over-provisioning (sometimes spelled as OP, over provisioning, or overprovisioning) is the difference between the physical capacity of the flash memory and the logical capacity presented through the operating system (OS) as available for the user. During the garbage collection, wear-leveling, and bad block mapping operations on the SSD, the ...
The operating system uses a four byte relative track and record (TTR) for some access methods and for others an eight-byte extent-bin-cylinder-track-record block address, or MBBCCHHR, Channel programs address DASD using a six byte seek address (BBCCHH) and a five byte record identifier (CCHHR). [citation needed]