Disk Sector Definition

A disk sector is a subdivision of a track (track) on a magnetic disk or an optical disk.Each sector stores a fixed amount of data.

Typically each sector provides a fixed space of 512 bytes (on hard drives and diskettes ), or 2048 bytes (on optical disks).

Newer hard drives use 4096 byte (4 KB) sectors, which are known as Advanced Format (AF), and are the units that most prevail today.

In English: disk sector.

Disk sector on hard drives

A group of disk sectors constitutes a disk block (also called disk cluster or sector group).

Many times the size of the disk sector can match the size of the disk block, for example, on a disk that uses 512-byte sectors, a block of 512-byte disk contains a sector.

The size can be configured when formatting a storage unit, in the allocation unit size option.

It can also be formatted by doing or that a block of disk has 4 kilobytes (KB) and this will contain eight sectors of 512 bytes.

As of 2007 the International Association of Disk Units, Equipment and Materials (IDEMA) recommends a size of 4 KB disk block, not advising the 512 bytes that had been used for the past 30 years.This allows better use of modern disks and also increase access speed and reduce errors.

Structure disk in (A) a track (red), (B) a geometric sector (blue), (C) a sector of a track (magenta), (D) a group of sectors or cluster (green).

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 cake slice.therefore, the disk sector (Figure 1, item C) refers to the intersection of a track and a geometric sector.

Characteristics of each physical sector of the hard disk

sector is the minimum storage unit of a hard disk.Most disk partition schemes are designed so that the files occupy an integral number of sectors, regardless of the actual size of the file.Files that do not fill an entire sector will have the rest of its last sector full of zeros.In practice, operating systems typically work with blocks of data that can span multiple sectors.

In modern disk drives, each physical sector consists of two basic parts, the sector header area (usually called "ID") and the data area.

The sector header or header contains information used by the converter and the controller; This information includes synchronization bytes, address identification, error indicator and error detection and correction information.The header can also include an alternative address that will be used if the data area is not reliable.The address identification is used to ensure that the mechanics of the unit have positioned the read/write head over the correct location.

The data area contains the synchronization bytes, user data and an error correction code ( ECC) used to check and possibly correct errors that may have been introduced into the data.

History

The first disk drive, the IBM 350 of 1957, had ten sectors 100 characters per track; Each character was six bits and included a parity bit.The number of sectors per track was identical on all recording surfaces.No identifying field (ID) associated with each sector was recorded.

disk storage IBM 1301 of 1961 introduced sectors of variable length, called records by IBM, and added to each record a record address field separate from the data in a record (sector).All modern disk drives have address fields sector, called ID fields, separated from the data of a sector.

Also in 1961 Bryant, with its 4000 series, introduced the concept of recording by zones, which allowed the number of sectors per track to vary depending on the diameter of the track: there are more sectors in an outer track than in an interior one, which became an industrial practice in the 1990s and is now standard.

The units of disk announced with the IBM System/360 in 1964 detected errors in all fields of their sectors (records) with a cyclic redundancy check (CRC) replacing parity detection by character of previous generations.IBM sectors (records) at this time added a third field to the physical sector, a key field to aid in the search for data.These physical sectors of IBM, called registers, have three basic parts, a Count field that acts as an ID field, a Key field not present in most disk drive sectors and a Data field, often called the CKD format for a record.

IBM 3330 1970 disk storage replaced the CRC in the sector data field with an error correction code (ECC) to improve the integrity of the data by detecting most of the errors and allowing the correction of many of them.Ultimately, all fields of the disk sectors had ECC.

Before the 1980s there were little standard zacion of sector sizes; The disk drives had a maximum number of bits per track and several system manufacturers subdivided the track into different sector sizes to suit their operating systems and applications.The popularity of the PC from the 80s and the advent of the interface IDE in the late 1980s led to a 512-byte sector becoming an industry-standard sector for hard drives and similar storage devices.

In the 1970s, IBM added the Fixed block architecture Direct Access Storage Devices (FAS DASDs) to its DASD line CKD.CKD DASD supports multiple sectors of variable length, while IBM FBA DASD supports sector sizes of 512, 1024, 2048 or 4096 bytes.

In 2000, the industry's commercial organization, International Disk Drive Equipment and Materials Association (IDEMA), began working to define the implementation and standards that would govern the size formats of the sector that and exceed 512 bytes to accommodate future increases in data storage capabilities.

At the end of 2007, anticipating a standard future of IDEMA, Samsung and Toshiba began sending hard disk drives from 1.8 inches with 4096 bytes sectors.

In 2010 IDEMA completed the Advanced Format standard for 4096 sector units, setting the transition date of the sectors from 512 to 4096 bytes in January 2011 for all manufacturers, and Advanced Format drives soon became dominant.

This image, taken from Wikipedia, shows the efficiency of the hard drive format with Advanced Format 4K technology and distributed ECC.CC License

For more information on this topic read: Advanced Format.

Sectors vs blocks

While the sector specifically means the physical area of the disk, the term block has been used loosely to refer to a small pe data dazo.The block has multiple meanings depending on the context.In the context of data storage, a file system block is an abstraction on disk sectors that may span multiple sectors.

In other contexts , it can be a unit of a data flow or an operation unit for a utility.For example, the Unix dd program allows you to set the block size to be used during execution with the parameter bs=bytes.This specifies the size of the pieces of data as delivered by dd, and is not related to the sectors or blocks of the file system.

In Linux, the size of the disk sector can be determined with fdisk-l | grep "Sector size" and block size can be determined with blockdev-getbsz/dev/sda

Disk sectors and allocation unit size

When formatting a hard drive, either using the basic Windows tools or through a free disk partitioning tool, you can define a custom allocation unit size (AUS).This essentially tells the file system what is the smallest portion of the disk that can be used to store data.

For example, in Windows, you can choose to format a hard disk in any of the following sizes: 512, 1024, 2048, 4096, or 8192 bytes, or 16, 32, or 64 kilobytes.

Suppose you have a 1 MB document file (1,000,000 bytes).You can store this document on something like a floppy disk that stores 512 bytes of information in each sector, or on a hard drive that has 4096 bytes per sector.It doesn't really matter how big each sector is, but only how big it is the entire device.

The only difference between the device whose allocation size is 512 bytes and 4096 bytes (or 1024, 2048, etc.), is that the 1 MB file must cover more sectors of the disk than in device 4096.This is because 512 is smaller than 4096, which means that there may be fewer "pieces" of the file in each sector.

In this example, if the 1 MB document is edited and now converted to a 5 MB file, this is an increase in size of 4 MB.If the file is stored on the disk drive using the 512 byte allocation unit size, parts of that 4 MB file will be extended by the hard drive to other sectors, possibly in sectors further away from the original group In addition to sectors that contain the first 1 MB, causing something called fragmentation.

However, using the same example as before but with the size of the 4096 byte allocation unit, fewer disk areas will contain the 4 MB of data (because each block size is larger), thus creating a group of sectors that are closer to each other, minimizing the likelihood of fragmentation.

In other words, a larger AUS It generally means that files are more likely to stay closer together on the hard drive, which in turn will result in faster disk access and better overall computer performance.

Damaged disk sector

One or more physically damaged sectors of the hard disk can occur due to blows that it has received or by simple use.A sudden power outage no longer damages modern hard drives, as if it could occur with the old ones of the 90s.

If there are bad sectors these can be marked s as such by hard disk scanning applications (Windows scandisk does), so that they are not used.

Anyway there are bad sectors is not a good signal for a hard disk and it is suggested to buy a new one.

Related terminology

• Advanced Format

Sources: WikipediaLifewire