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In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. For most disks, each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs), and 2048 bytes for CD-ROMs, DVD-ROMs and BD-ROMs. [1]
Since the first sector of a disk is sector zero, the first 64 sectors are sectors 0 to 63. The first sector of Track0 is known as the master boot record (MBR) and contains the initial code used to boot the operating system (bootstrap code). Near the end of the MBR is the Partition Table: a predefined structure containing the layout of the disk.
Floppy disks and controllers had used physical sector sizes of 128, 256, 512 and 1024 bytes (e.g., PC/AX), but formats with 512 bytes per physical sector became dominant in the 1980s. [ 3 ] [ 4 ] The most common physical sector size for hard disks today is 512 bytes, but there have been hard disks with 520 bytes per sector as well for non-IBM ...
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
(B) Geometrical sector (C) Track sector (D) Cluster. A disk drive track is a circular path on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read. A track is a physical division of data in a disk drive, as used in the Cylinder-Head-Record (CCHHR) addressing mode of a CKD disk.
For simplicity and maximum performance, the logical sector size is often identical to a disk's physical sector size, but can be larger or smaller in some scenarios. The minimum allowed value for non-bootable FAT12/FAT16 volumes with up to 65,535 logical sectors is 32 bytes, or 64 bytes for more than 65,535 logical sectors.
Still later, magnetic hard disks employed an evolution of LBA where the size of the addressable disk sectors can differ from the physical block size. For example, Advanced Format (AF) 512e HDDs use 4096-byte physical sectors, while their firmware provides emulation for a virtual sector size of 512 bytes; thus, "512e" stands for "512-byte ...
The sector unit is the smallest size of data to be stored in a hard disk drive, and each file will have many sector units assigned to it. The smallest entity in a CD is called a frame, which consists of 33 bytes and contains six complete 16-bit stereo samples (two bytes × two channels × six samples = 24 bytes).