How does hard disk store digital data?
This article gives you exposure about how hard disk store/write and read data into digital format in magnetic layer over pallets of hard disk. Each hard disk is having its own storing capacity based on the number of pallets or round disk having magnetic material layer on which information is written and read. The inside components are shown in the figure given below.
In today's era, it is impossible to think of any digital application that does not involve any digital information in the form of reading and writing. Each digital device uses memory to store the digital data in the form of binary digits like zero and one. Since the invention of the hard disk over the 50 years back, it is now an integrated part of any digital circuit or device, say the personal computer, laptop, music player whether it is iPad, mobile phones, pen drives and memory cards, each one of them uses the same principle of writing and reading of digital data. Today's computer's integrated device called hard disk has much more capacity in GB (Giga Bytes) that even thought possible by our father and grandfather. Today's hard disk has incredible memory capacity in terms of thousands of CDs, DVDs. Hard disk storage uses the principle of magnetism to store digital data. Digital data can be of any type like a music file, image file, text file or any software file they all use binary forms and information can be written in the form of magnetism in a platter. How does magnetism helps to store the digital information?
We can take a simple example to learn how does magnetism helps in storing digital data. Consider an unmagnetized iron nail and you want to use it to convey some information about your future presence in Sunday's function at your friend's home. To convey this information to your friend, you will tell this to your friend that if nail in your mailbox is magnetized, you will come otherwise you will not come. Meaning magnetized nail conveys positive response (one) and demagnetized nail conveys negative (zero) response. In the same way, digital information is written in binary digits of zero and one. Our personal computer and other devices understand only the language of binary. Our hard disk is nothing but a box which contains billions of microscopically small iron nails. Each iron nail is nothing but small or tiny information in the form of zero and one. This is called a bit and eight bits make a byte and so on. Thus binary number can be easily represented by micro iron nail with its magnetism property.
If the iron nail is magnetized, it represents one (1) and if it is demagnetized, it represents zero (0). Thus 12 can be represented by 1100 means it uses two magnetized nails and two demagnetized nails placed alongside each other. This is the same way hard disk store the information in digital form of binary system. Constructional features of hard disk
A hard disk is an assembly of many important components put together to work as a single storage unit. Each hard disk contains shiny and circular plate called platter which is divided into billions of parts called tracks. Each part of the platter is independently magnetized or demagnetized to store one or zero respectively. This magnetism will last even after the power of the device is switched off means platter retains the digital information intact by magnetism. The platter can be one or more in number depending on the size of the hard disk and its storage capacity. Platter is simply a disk made from aluminum or glass like hard material and which is coated with a thin metal layer which can be alternately magnetized or demagnetized. A hard disk is also having an arm mechanism which is having read-write head which can be easily moved back and forth over platters to read and write the digital information stored by magnetism. There are two read-write head for each platter. One is for reading at the top surface and second at the bottom to read the bottom surface. A layer of fluid or air is used to reduce wear and tear of read-write heads. Actuator with electric motor moves the read-write head/arm. Central spindle in hard disk allows the platters to rotate at very high speed in thousands of revolutions so that information can be easily and fast accessible. Plug connection joins the hard disk to motherboard/circuit board. The function of the Circuit board which is underside is to control and maintain the data flow to and from the platter plates. The flexible connector is used to carry the data from the circuit board to read-write head and platter plates. 
How does hard disk store the data?
Once the information is stored or written in material of platter or hard disk, the important and difficult task is to retrieve it. You can imagine a finding of a single magnetized iron nail from a huge collection of unmagnetized iron nails. The unmagnetized iron nails are nothing but free space or zeros. When hard disk writes the data, it does this function very smartly by storing the data in some patter on platter and they are called tracks and which is made up of sectors. File Allocation Table (FAT) is a map of information stored in the hard disk, it tells which part of the hard disk is used up and which is still free. When you write some new files, map is executed for reference and thus free space is found in a platter for new writing and same is for reading process or retrieving process. Some safety tips for hard disk
Do not use your computer in dusty or in dirty environment as dirt or dust may damage the platter. If some of these dust or dirt comes under the read-write head, it bounces like up and down and thus it damages platter and information too, Sometimes whole hard disk is said to crash – disk crash/head crash. Always have a habit of backing up the data from hard disk in some other means for future reference.
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Thank you so much for this informative article. You have very well explained how the digital information is stored in a magnetic storage device. I have been studying these things in my MCA. This article has helped me a lot in understanding the basics of storage of digital data.
Keep on writing such articles. Looking forward for more such articles.