Every track is divided into several arcs and these arcs are sectors in disk.

Brief Introduction
Data is read and written in disk by unit of sector in disk drive while dos system allocates disk space in unit of cluster. A disk cluster is several sectors usually, and it is related to disk types, DOS editions and sizes of partitions. Every cluster is only taken up by one file; even this file contains a few bites. That two or more files take up the same cluster is forbidden because it will cause chaos of data. These allocation systems in minimum unit of cluster make it easier to manage data, but it causes waste of disk space as well. Especially when there are a lot of small files, the waste space of a disk of 1GB can be hundreds MB.
As is known to all, the operating system stores the information in the form of sectors. And every sector contains the data of 512 bytes and some other information. It has two major part: identifier of location and data segment of data storage. The identifier is the head of sector and it contains 3 numbers (Heads, Cylinders and sectors) constituting 3D address. The head also contains a field that indicates whether the sector can store data reliably or whether the failed unsuitable sign is found. In some disk controller, there is pointer recorded in the head of sector. It can guide the disk to the replaced sector or track when the original sector fails. Finally, sector head ends with the value of CRC. So the controller can examine the read situation of head and guarantee the The second major part of sector is data segment for data storage. It can be divided into data and ECC for data protection. During the original preparation, 512 virtual bites and the corresponding ECC number are written in this part.
The head of sector also contains a sector number that can identify this sector in the track. Interestingly, these sector numbers are not physically continuous, and they are not appointed as particular order. The sector number varies form 1 to a certain value and it can be 255 in some cases. However, disk controller does not concern which number are arranged in which sector head. Even in particular condition, sectors can use the same number. No matter how big the data field is, the disk controller only reads the data it finds out or writes the data ordered.



The total number of disk sector is shown clearly by the third-party partition manager in the picture. And this software can also be applied to adjust the size of partition and to move and copy partitions as well. MiniTool Partition Wizard that is free for individual and family users. It also provides detailed helps on voice and video operation for those who are unfamiliar with computer operation, which helps them to be familiar with computer.