How Data is stored on Hard Disk

            Hard disk is a common data storage used in computers. Data is stored on the hard disk in the form of 0 and 1. Through this article we will find out how actually data is stored on the hard disk drive.  The part of the hard disk that stores the data is known as platter. Platters are circular disk made of a non magnetic material typically aluminum alloy, glass or ceramic and are coated with a thin layer (10-20nm) of a magnetic material. Platters are further separated in to the tracks and sectors where tracks are concentric circles while sectors are pie shaped wedges on the track.

       Hard disk stores information in the form of magnetic fields. Data is stored digitally in the form of tiny magnetized regions on the platter where each region represents a bit. To write a data on the hard disk, a magnetic field is placed on the tiny field in one of these two polarities: N-S – If North Pole arrives before the south pole and S-N – if the south pole arrives before the north pole while the field is accessed.  An orientation in the one direction (like N-S) can represent the ‘1’ while the opposite orientation (S-N) represents “0”. This polarity is sensed by integrated controllers built within the hard disk.

Construction of Hardisk & Storing Mechanism :-
Data Storage Example

    Imagine that someone is saving a 1-Mb Word document on the hard disk. Saving a 1 MB file means the disk will systematically ‘fill in’ a thousand squares.

      After saving the Word document, assume that a 3 MB photo is saved to a hard disk. Following the key data storage concepts, the disk writer head will go through the disk and look for the first available space, which, in this example, happens to be the square following the Word document’s last kilobyte. Thus, the 3 MB photo will be saved in the space next to the Word document.

           Afterward, go back to the Word document and trim it down, ending up with a file 700 KB in size, which is then saved to the hard disk. Given the smaller file size, the 1 MB space requirement was reduced to 700 KB, leaving 300 KB free or (using the analogy above) 300 blank squares immediately after the Word document. There is now available space between the Word Document and the 3 MB photo.

           When yet another file is saved, say a 2 MB Excel file, the hard disk will follow its rule of saving data on the first available space. Thus, the Excel file will be split into two portions: 300 KB will be written on the 300 KB free space and the rest will be placed in the next available space, after the image file.


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