Hard disk drives – What is a HDD – How it works

Hard Disk Drive

What is a Hard disk drive?

Hard disk drives are the storage devices that use magnetic storage to retrieve and store the digital information using a rapidly and rigidly rotating disk coated with magnetic material. HDDs are a non-volatile memory that means they store data even in the absence of power.

How Hard disk drives store data?

The data on the hard disk drives is stored in the form of binary numbers that is 0s and 1s. The rapidly rotating disks (platters) inside the hard disk drives store data by aligning the magnetism of bits in one or the other direction. Directions represent 1s and 0s. If one direction represents a ‘0’ then the other will represent a ‘1’.  Below is byte representing 8 bits and the arrows are representing the direction of magnetism. Suppose arrow facing upward represents a ‘1’ and arrow facing downward represents a ‘0’, so the following byte will represent the code 10111000.

one byte.png

1 byte = 8 bits

But, how do these 1s and 0s make any sense?

Independently these bits don’t make any sense, but when combined together they form patterns that are recognized by the computer and computer displays or processes the data and information with the help of these patterns.

For example – the following bytes represents the English alphabets.

01000001 – A

01000010 – B

01000011 – C

Modern Hard disk drives contains billions or even trillions of bits. Computer with the help of good algorithms recognize the patterns in these bytes, joins them to form useful information that can be read and understood by the humans.

How data is written on the platters in the Hard disk drives?

Hard disk drives have two motors, one motor for spinning disks (platters) and an actuator (motor) that positions the read/write head assembly across the spinning disks. The read/write head moves across the spinning disk, it is placed very near to the surface of the platter and it interacts with the bits. It uses magnetic field to read, write or change the direction of the magnetism in a bit. One bit can either be a ‘0’ or a ‘1’. The actuator gets the address of data, moves read/write head to that address point on the spinning platters and either make changes to it or just read that bits and transfer data to the CPU.

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