Physical Disk Structure

Disk Structure:

                          Disk drives are addressed as large 1-dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer the 1-dimensional array of logical blocks is mapped into the sectors of the disk sequentially – Sector 0 is the first sector of the first track on the outermost cylinder – Mapping proceeds in order through that track, then the rest of the tracks in that cylinder, and then through the rest of the cylinders from outermost to innermost.

Physical Disk Structure

Cylinder 
The disc that makes up the hard disk is divided into tracks; tracks of all discs which have same track value are called a cylinder, so the cylinder is a pile of tracks with same track value of a hard disk. 

Head 
Normally, a disc has two heads for reading or writing data, one is for the top and the other one is for the opposite side; the head value means the disc location and side. 

Sector 
A track is composed of sectors and the number of sectors of all tracks on the hard disk is the same.Sector is the minimal storage unit of a hard disk; the size of one sector is always 512 bytes (rarely, it might be 1024, 2048 or 4096 bytes in some special hard disks).