Hard disks use rotating platters coated with magnetic material to store data in tiny magnetic regions called sectors. Multiple sectors are grouped into clusters to store files. Each platter has two readable surfaces and a read/write head can access one track on each surface. When the heads pass over a region during rotation, they can detect the magnetic polarity to read or change data in the sectors. Hard disks can store much more data than floppy disks and retain data when powered off.

1. Hard DiskWhat is it ?A hard disk is a secondary storage device used on your computer to store large amounts of data. The data is kept even when the power is turned off on the computer.Information stored on disks can be stored indefinitely. A floppy disk can store data as well, but they are limited as to the amount they can store.The round plate-like things are called platters. Each platter has 2 sides, each side being called a head. The part that looks like a record player needle is a Read/Write head. This is a different type of head (a little confusing). This part is what moves back and forth along a head on a platter reading and writing data. The platters rotate around a spindleThe platters & SpindleOn a hard disk, data is stored in thin, concentric bands. A drive head, while in one position can read or write a circular ring, or band called a track. There can be more than a thousand tracks on a 3.5-inch hard disk. Sections within each track are called sectors. A sector is the smallest physical storage unit on a disk, and is almost always 512 bytes (0.5 kB) in size.The figure below shows a hard disk with two platters.Prepared By :-JemisJivani(09BCE017)-RushabhKamdar(09BCE019)

2. Sector & ClusterA sector, being the smallest physical storage unit on the disk, is almost always 512 bytes in size. Sector identification data is written to the area immediately before the contents of the sector and identifies the starting address of the sector.A cluster can consist of one or more consecutive sectors. The number of sectors is always an exponent of 2. They are called clusters because the space is reserved for the data contentsRead & Write HeadsThe read/write heads are mechanisms that allow the hard disk to read and write information and data. There is one head on every side of a platter.How does the hard disk store data?On each of the platters there is a thin layer of magnetic film. Data storage on hard disks is very similar to that of a cassette tape. Data is stored in many 1's and 0's. These binary digits are arranged in different ways to represent different characters. When these are read back by the head the data is retrieved and processed.