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In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and DVD-ROMs. Newer HDDs use 4096-byte (4 KiB) sectors, which are known as the Advanced Format (AF). Geometrically, the word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), which is shaped like a slice of a pie. Thus, the ''disk sector'' (Figure 1, item C) refers to the intersection of a ''track'' and geometrical ''sector''. In disk drives, each physical sector is made up of three basic parts, the sector header, the data area and the error-correcting code (ECC). The sector header contains information used by the drive and controller; this information includes sync bytes, ''address identification'', flaw flag and header parity bytes. The header may also include an alternate address to be used if the data area is undependable. The ''address identification'' is used to ensure that the mechanics of the drive have positioned the read/write head over the correct location. The data area contains the recorded user data, while the ECC field contains codes based on the data field, which are used to check and possibly correct errors that may have been introduced into the data. == History == Early in the computing industry, the term ''block'' was loosely used to refer to a small chunk of data. Later the term referring to the data area was replaced by sector, and block became associated with the data packets that are passed in various sizes by different types of data streams. For example, the Unix program dd allows one to set the block size to be used during execution with the parameter bs=bytes. This specifies the size of the chunks of data as delivered by dd, and does not affect the size of the sectors used by the medium to which the data is stored.The standard sector size of 512 bytes for magnetic disks was established with the inception of the hard disk drive in 1956. In 2000, through a coordinated effort organized by the industry trade organization, ''International Disk Drive Equipment and Materials Association'' (IDEMA), leading hardware and software companies started work to define the implementation and standards that would govern sector size formats exceeding 512 bytes to accommodate future increases in data storage capacities.〔(【引用サイトリンク】 The Advent of Advanced Format )〕 In the 1970s IBM introduced the Direct Access Storage Device (DASD) with fixed-block architecture using sizes of 512, 1024, 2048, or 4096 bytes. Cray Research had an 819 disk controller in 1975 that transferred 512 64-bit words (4096 bytes) per sector. Later, hard disk drives supporting 1,024-byte sectors began to be integrated into consumer electronics devices such as portable media players and digital video cameras. However, by far the majority of hard drives shipped up to the start of the 2010s still used the traditional 512-byte sector size. By the end of 2007, Samsung and Toshiba began shipments of 1.8-inch hard disk drives with 4096 byte sectors, the sector size designated as the next standard format for all hard drives. In 2010, the International Disk Drive Equipment and Materials Association (IDEMA) completed the Advanced Format standard for 4096 sector drives,〔 setting the date for the transition from 512 to 4096 byte sectors as January 2011 for all manufacturers, and Advanced Format drives soon became prevalent. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Disk sector」の詳細全文を読む スポンサード リンク
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