What is Logical Block Addressing (LBA)?

Logical Block Address (LBA)

Logical block addressing is a technique that allows a computer to address a hard disk larger than 528 megabytes. A Logical Block Address (LBA) is a 28-bit value that maps to a specific cylinder-head-sector address on the disk. 28 bits allows sufficient variation to specify addresses on a hard disk up to 8.4 gigabytes in data storage capacity.

The term “Logical block addressing” can also be defined as

  1. An address that defines where data is stored on the hard drive.
  2. A common scheme used for specifying the location of blocks of data stored on computer storage devices.
  3. A run-time function of the system BIOS. The BIOS uses LBA for the following commands: read (with and without retries), read verify, read long, write (with and without retries), write verify, write long, read multiple, write multiple, read DMA, write DMA, seek, and format track.

What is Storage?

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In a computer, storage is the place where data is held in an electromagnetic or optical form for access by a computer processor. There are two general usages.

  1. Storage is frequently used to mean the devices and data connected to the computer through input/output operations – that is, hard disk and tape systems and other forms of storage that don’t include computer memory and other in-computer storage. For the enterprise, the options for this kind of storage are of much greater variety and expense than that related to memory. This meaning is probably more common in the IT industry than meaning 2 (the following).
  2. In a more formal usage, storage has been divided into:
    1. Primary storage, which holds data in memory (sometimes called random access memory or RAM) and other “built-in” devices such as the processor’s L1 cache, and
    2. Ssecondary storage, which holds data on hard disks, tapes, and other devices requiring input/output operations.

Primary storage is much faster to access than secondary storage because of the proximity of the storage to the processor or because of the nature of the storage devices. On the other hand, secondary storage can hold much more data than primary storage.

In addition to RAM, primary storage includes read-only memory (ROM) and L1 and L2 cache memory. In addition to hard disks, secondary storage includes a range of device types and technologies, including diskettes, Zip drives, redundant array of independent disks (RAID) systems, and holographic storage. Devices that hold storage are collectively known as storage media.

A somewhat antiquated term for primary storage is main storage and a somewhat antiquated term for secondary storage is auxiliary storage. Note that, to add to the confusion, there is an additional meaning for primary storage that distinguishes actively used storage from backup storage.

Interview Question : What is Hard Disk?

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A hard disk is part of a unit, often called a “disk drive,” “hard drive,” or “hard disk drive (HDD),” that stores and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces. Today’s computers typically come with a hard disk that contains several billion bytes (gigabytes) of storage.

A Hard disk can also be defined as:

  1. a rigid (“hard”) non-removable magnetic disk with a large data storage capacity.
  2. a data storage device used for storing and retrieving digital information using one or more rigid (“hard”) rapidly rotating disks (platters) coated with magnetic material.
  3. A magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft, or floppy disk. Hard disks hold more data and are faster than floppy disks.

Extra Information

A hard disk is really a set of stacked “disks,” each of which, like phonograph records, has data recorded electromagnetically in concentric circles or “tracks” on the disk. A “head” (something like a phonograph arm but in a relatively fixed position) records (writes) or reads the information on the tracks. Two heads, one on each side of a disk, read or write the data as the disk spins. Each read or write operation requires that data be located, which is an operation called a “seek.” (Data already in a disk cache, however, will be located more quickly.)

A hard disk/drive unit comes with a set rotation speed varying from 4500 to 7200 rpm. Disk access time is measured in milliseconds. Although the physical location can be identified with cylinder, track, and sector locations, these are actually mapped to a logical block address (LBA) that works with the larger address range on today’s hard disks.

To know more regarding the terms follow the post about Difference between Disc and Disk click here.