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Disk sector
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. Newer HDDs and SSDs use 4096 byte (4 KiB) sectors, which are known as the Advanced Format (AF).
The sector is the minimum storage unit of a disk drive. Most disk partitioning schemes are designed to have files occupy an integral number of sectors regardless of the file's actual size. Files that do not fill a whole sector will have the remainder of their last sector filled with zeroes. In practice, operating systems typically operate on blocks of data, which may span multiple sectors.
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 modern disk drives, each physical sector is made up of two basic parts, the sector header area (typically called "ID") and the data area. The sector header contains information used by the drive and controller; this information includes sync bytes, address identification, flaw flag and error detection and correction information. 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 sync bytes, user data and an error-correcting code (ECC) that is used to check and possibly correct errors that may have been introduced into the data.
The first disk drive, the 1957 IBM 350 disk storage, had ten 100 character sectors per track; each character was six bits and included a parity bit. The number of sectors per track was identical on all recording surfaces. There was no recorded identifier field (ID) associated with each sector.
The 1961 IBM 1301 disk storage introduced variable length sectors,[disputed (for: the literature does not use the term sector for variable-length blocks) – discuss] termed records or physical records by IBM, and added to each record a record address field separate from the data in a record. All modern disk drives have sector address fields, called ID fields, separate from the data in a sector.
Also in 1961 Bryant with its 4000 series introduced the concept of zoned recording (ZBR) which allowed the number of sectors per track to vary as a function of the track's diameter – there are more sectors on an outer track than on an inner track. In the late 1980s ZBR was again used in disk drives then announced by Imprimis and Quantum and by 1997 its industry usage was ubiquitous.
The disk drives and other DASDs announced with the IBM System/360 in 1964 used self-formatting variable length sectors,[disputed (for: the literature does not use the term sector for variable-length blocks) – discuss] termed records or physical records by IBM. They detected errors in all fields of their records with a cyclic redundancy check (CRC) replacing parity per character detection of prior generations. These IBM physical records have three basic parts, a Count field which acts as an ID field, an optional Key field to aid in searching for data and a Data field; in practice, most records had no Key field, indicated by a key length of zero. The structure of these three fields is called the CKD track format for a record.
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Disk sector AI simulator
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Disk sector
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. Newer HDDs and SSDs use 4096 byte (4 KiB) sectors, which are known as the Advanced Format (AF).
The sector is the minimum storage unit of a disk drive. Most disk partitioning schemes are designed to have files occupy an integral number of sectors regardless of the file's actual size. Files that do not fill a whole sector will have the remainder of their last sector filled with zeroes. In practice, operating systems typically operate on blocks of data, which may span multiple sectors.
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 modern disk drives, each physical sector is made up of two basic parts, the sector header area (typically called "ID") and the data area. The sector header contains information used by the drive and controller; this information includes sync bytes, address identification, flaw flag and error detection and correction information. 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 sync bytes, user data and an error-correcting code (ECC) that is used to check and possibly correct errors that may have been introduced into the data.
The first disk drive, the 1957 IBM 350 disk storage, had ten 100 character sectors per track; each character was six bits and included a parity bit. The number of sectors per track was identical on all recording surfaces. There was no recorded identifier field (ID) associated with each sector.
The 1961 IBM 1301 disk storage introduced variable length sectors,[disputed (for: the literature does not use the term sector for variable-length blocks) – discuss] termed records or physical records by IBM, and added to each record a record address field separate from the data in a record. All modern disk drives have sector address fields, called ID fields, separate from the data in a sector.
Also in 1961 Bryant with its 4000 series introduced the concept of zoned recording (ZBR) which allowed the number of sectors per track to vary as a function of the track's diameter – there are more sectors on an outer track than on an inner track. In the late 1980s ZBR was again used in disk drives then announced by Imprimis and Quantum and by 1997 its industry usage was ubiquitous.
The disk drives and other DASDs announced with the IBM System/360 in 1964 used self-formatting variable length sectors,[disputed (for: the literature does not use the term sector for variable-length blocks) – discuss] termed records or physical records by IBM. They detected errors in all fields of their records with a cyclic redundancy check (CRC) replacing parity per character detection of prior generations. These IBM physical records have three basic parts, a Count field which acts as an ID field, an optional Key field to aid in searching for data and a Data field; in practice, most records had no Key field, indicated by a key length of zero. The structure of these three fields is called the CKD track format for a record.