A difficult disk is a sealed unit containing a number of platters in a stack. Tough disks may be an installed in a horizontal or a upright position. In this description, the hard drive is an installed horizontally.

You are watching: How many bytes in a sector

Electromagnetic read/write heads are positioned above and below each platter. Together the platters spin, the journey heads move in towards the center surface and out towards the edge. In this way, the journey heads have the right to reach the whole surface of each platter.

Making Tracks

On a tough disk, data is save in thin, concentric bands. A drive head, while in one position have the right to read or create a circular ring, or band called a track. There have the right to be more than a thousand monitor on a 3.5-inch hard disk. Part within each track are called sectors. A ar is the smallest physical storage unit on a disk, and is virtually always 512 bytes (0.5 kB) in size.

The figure listed below shows a hard disk v two platters.

Parts that a difficult Drive


The structure of older tough drives (i.e. Before Windows 95) will describe a cylinder/ head/ ar notation. A cylinder is formed while all drive heads room in the same place on the disk.

The tracks, stacked on top of each other form a cylinder. This plan is progressively being removed with contemporary hard drives. All brand-new disks use a translation aspect to do their actual hardware layout show up continuous, as this is the means that operating solution from windows 95 onward prefer to work.

To the operating device of a computer, tracks are logical quite than physical in structure, and are created when the disk is low-level formatted. Tracks room numbered, starting at 0 (the outermost leaf of the disk), and also going approximately the greatest numbered track, commonly 1023, (close come the center). Similarly, there are 1,024 cylinders (numbered from 0 to 1023) ~ above a difficult disk.

The ridge of platters turn at a continuous speed. The journey head, when positioned close come the facility of the disk reads indigenous a surface that is happen by more slowly 보다 the surface ar at the external edges the the disk.

To compensate for this physics difference, tracks near the outside of the disk room less-densely inhabited with data than the tracks close to the facility of the disk. The an outcome of the various data density is the the same amount of data can be review over the same duration of time, from any type of drive head position.

The disk space is filled v data follow to a standard plan. One side of one platter contains space reserved because that hardware track-positioning information and is not accessible to the operating system. Thus, a decaying assembly containing two platters has three sides easily accessible for data. Track-positioning data is written to the disk throughout assembly in ~ the factory. The device disk controller reads this data to place the journey heads in the exactly sector position.

Sectors and Clusters

A sector, being the smallest physical storage unit on the disk, is virtually always 512 bytes in size due to the fact that 512 is a power of 2 (2 come the strength of 9). The number 2 is used because there are two claims in the most basic of computer languages — on and off.

Each disk ar is labelled making use of the factory track-positioning data. Sector to know data is composed to the area automatically before the contents of the sector and also identifies the beginning address of the sector.

The optimal technique of storing a paper on a disc is in a contiguous series, i.e. All data in a stream save end-to-end in a solitary line. As numerous files are bigger than 512 bytes, it is approximately the paper system come allocate sectors to save the file"s data. For example, if the paper size is 800 bytes, two 512 k sectors room allocated for the file.

A cluster can consist the one or more consecutive sectors. The variety of sectors is constantly an exponent that 2. A cluster could consist that 1 sector (2^0), or, much more frequently, 8 sectors (2^3). The only odd number a that sectors a cluster might consist that is 1. It can not be 5 sectors or an even number that is no an exponent of 2. It would not it is in 10 sectors, yet could it is in 8 or 16 sectors.

They are referred to as clusters due to the fact that the space is scheduled for the data contents. This procedure protects the save on computer data from gift over-written. Later, if data is appended to the document and its dimension grows come 1600 bytes, an additional two clusters space allocated, save on computer the entire file within four clusters.


If contiguous clusters room not accessible (clusters the are adjacent to each various other on the disk), the 2nd two clusters may be written somewhere else on the very same disk or in ~ the exact same cylinder or on a various cylinder — wherever the file system finds 2 sectors available.

A paper stored in this non-contiguous way is thought about to be fragmented. Fragmentation deserve to slow down system performance if the document system must straight the drive heads come several various addresses to discover all the data in the document you want to read. The extra time because that the heads to take trip to a variety of addresses reasons a hold-up before the entire record is retrieved.

Cluster size have the right to be adjusted to optimize paper storage. A bigger cluster dimension reduces the potential because that fragmentation, however increases the likelihood that clusters will have actually unused space. Utilizing clusters larger than one sector reduces fragmentation, and reduces the quantity of disk room needed to save the information around the used and also unused areas on the disk.

Most disks used in personal computers today turn at a continuous angular velocity. The tracks near the exterior of the disk are less densely lived in with data than the tracks close to the facility of the disk. Thus, a solved amount of data deserve to be check out in a consistent period that time, also though the rate of the disk surface ar is quicker on the tracks located more away indigenous the facility of the disk.

Modern disks reserve one side of one plate for track positioning information, which is composed to the disk in ~ the factory throughout disk assembly.

See more: Thanks For Letting Me Know., Thank You For Letting Me Know Correct

It is not obtainable to the operation system. The disk controller provides this details to fine song the head places when the heads move to another location top top the disk. When a side has the track position information, the side cannot be provided for data. Thus, a decaying assembly containing two platters has three sides that are available for data.