In computer diskette storage, a sector is part of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of data that users can access, typically 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and DVD-ROMs. The newer HDDs use a 4096-byte sector (4Ã, KiB), known as Advanced Format (AF).
This sector is the minimum storage unit of the hard drive. Most disk partitioning schemes are designed to have files that occupy the sector integral numbers regardless of the actual file size. Files that do not fill entire sectors will have the last remaining sector filled with zero. In practice, the operating system usually operates on a data block, which can reach many sectors.
Geometrically, the word sector means the part of the disc between the center, two spokes and the corresponding arc (see Figure 1, point B), which is shaped like a piece of cake. Thus, the disk sector (Fig. 1, item C) refers to the intersection of the track and the geometry sector .
In modern disk drives, each physical sector consists of two basic parts, sector header area (usually called "ID") and data area. The sector header contains information used by drives and controllers; this information includes sync bytes, address identification , flaw flag and error detection and correction information. The header can also include an alternate address that will be used if the data area is unreliable. Address identification is used to ensure that the drive mechanism has positioned the read/write head above the correct location. The data area contains the synchronization byte, user data and error correction code (ECC) used for checking and possibly correcting errors that may have been introduced into the data.
Video Disk sector
History
The first disk drive, IBM 350 350 1957 disk storage has ten sectors of 100 characters per track; each character is six bits and includes parity bits. The number of sectors per track is identical on all recording surfaces. There is no identifiers field identifier (ID) associated with each sector.
The disk storage IBM 1301 1961 introduced a variable length sector, called a record by IBM, and added to each record a separate recording address field from the data in the records (sectors). All modern disk drives have sector address fields, called ID columns, separate from data in a sector.
Also in 1961 Bryant with the 4000 series introduced the concept of recording zoning which allowed the number of sectors per track to vary as a function of the track diameter - there are more sectors on the outer track than on the inner track. It became an industry practice in the 1990s and became the current standard.
The disc drives announced with IBM System/360 in 1964 detected errors in all their sector fields (records) with a cyclic redundancy check (CRC) replacing parity per character detection from previous generations. The IBM sectors (records) currently add a third field to the physical sector, key areas to help search the data. This IBM physical sector, called a record, has three basic parts, the Count field that serves as the ID field, the Key field does not exist in most disk drive sectors and Data fields, often called CKD formats for records.
IBM 3330 1970 hard disk storage replaces the CRC in the sector data field with error correction codes (ECC) to improve data integrity by detecting most errors and allowing correction of many errors. Finally all areas of the disk sector have ECC.
Before the 1980s there was little standardization of sector size; disk drives have the maximum number of bits per track and various system manufacturers split the tracks into different sector sizes to customize the OS and their applications. The popularity of PCs that started in the 1980s and the rise of IDE interfaces in the late 1980s caused the 512-byte sector to be the industry-standard sector size for HDDs and similar storage devices.
In the 1970s IBM added a fixed device architecture of Direct Access Storage (FBA DASD) to the DASD CKD line. CKD DASD supports multiple sectors with variable lengths while IBM FBA DASD supports sector sizes of 512, 1024, 2048, or 4096 bytes.
In 2000, the industry trade organization The International Disk Equipment and Materials Association (IDEMA) began work to determine implementations and standards that would set the sector size format to exceed 512 bytes to accommodate future data storage capacity upgrades. In late 2007 to anticipate IDEMA standards in the future, Samsung and Toshiba began shipping a 1.8-inch hard disk drive with 4096 bytes of sector. In 2010 IDEMA completed the Advanced Format standard for 4096 sector drives, setting the date for transition from sector 512 to 4096 bytes as January 2011 for all manufacturers, and Advanced Format drives soon became prevalent.
Maps Disk sector
Sector versus block
While a special sector means a physical disk area, the term block has been used loosely to refer to a small piece of data. Blocks have many meanings depending on the context. In the context of data storage, the filesystem block is an abstraction of the disk sector that may span multiple sectors. In another context, it may be a unit of data flow or an operating unit for utilities. For example, the Unix dd program allows one to set the block size to be used during execution with the bs = bytes parameter. It specifies the size of the data portion that is sent by dd, and is not related to the sector or file system block.
In Linux, the size of the disk sector can be determined by fdisk-l | grep "Size size" and block size can be specified with blockdev --getbsz/dev/sda .
Zone bit record
If a sector is defined as the intersection of radius and trajectories, as is the case with early hard drives and most floppy disks, the sectors heading out of the disc are physically longer than those closer to the spindle. Since each sector still contains the same number of bytes, the outer sector has a lower bit density than the deep, which is the use of inefficient magnetic surfaces. The solution is a bit zone record, where the disk is divided into zones, each covering a small number of adjacent tracks. Each zone is divided into several sectors so each sector has the same physical size. Since the outer zones have a larger circumference than the inner zone, they are allocated more sectors. This is known as a zoned bit rate.
The consequence of zoning of zone bits is that the adjacent reading and writing feels faster on the outer track (corresponding to the lower block address) than on the inner track, as more bits pass under the head with each rotation; this difference can be 25% or more.
Advanced Format
Hard disk drive manufacturers identify the need for large sector sizes to provide higher capacity points along with enhanced error correction capabilities. The traditional way to achieve increased storage capacity, which averages 44 percent per year from 2000 to 2009, is projected to be stagnant without a revolutionary breakthrough in magnetic recording technology. However, by modifying the length of the data field through the implementation of the Advanced Format using a 4096-byte sector, hard disk drive manufacturers can increase the efficiency of the data surface area by five to thirteen percent while increasing the strength of ECC.
See also
References
Source of the article : Wikipedia
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