The average $500 laptop offers 256GB of storage. You might see that figure and think, "Wow—imagine all the movies, songs, and images I could save on that baby," right?

But did you ever think about how your data is stored?

Well, the answer might shock you as the hard drive on your system uses magnetism to store data. When compared to a CD, this approach is more efficient. In fact, if you were to stack the equivalent capacity of CDs in front of you, it would surely rise to eye level.

Which begs the question: How does a hard drive work?

How Does a Hard Drive Work?

To fully understand a hard drive, you have to know how one works physically. Basically, there are discs, one on top of the other, spaced a few millimeters apart. These discs are called platters. Polished to a high mirror shine and incredibly smooth, they can hold vast amounts of data.

Next, we have the arm. This writes and reads data onto the disc. It stretches out over the platter and moves over it from center to edge, reading and writing data to the platter through its tiny heads, which hover just over the platter. The arm, on average domestic drives, can oscillate around 50 times per second. This figure can rise into the thousands on many high-spec machines and those used for complex calculations.

Open mechanical hard drive

To put things into perspective, for hard drives running at 5,400 RPM, the arm travels 62 miles an hour. Also, the arm is only 10 nanometres away from the platter, and it is at this distance that the arm has to read and write data on the platter.

To perform this task, hard drives use the concepts of magnetism, and to understand how a hard drive works, we need to revisit some basics.

Magnetism in Hard Drives Explained

Before getting into hard drives, let's understand the concepts that hard drives use to store data.

Put simply, hard drives use ferromagnetism to save all your files in seconds. But what is ferromagnetism?

Do you remember keeping a set of paper clips close to a magnet overnight only to discover that the paper clips now behave like magnets? This behavior of certain metals acquiring magnetic properties when placed close to magnets is known as ferromagnetism. This change in metals' properties is used to store data on your hard drive.

metal screws stuck to a magnet

Although the platter on your drive looks like a mirror beneath the surface, it consists of trillions of grains. These grains have properties similar to the paper clips we discussed earlier and can store magnetic information when they come close to a magnetic field. To store information, these grains can have two different states, and these states are known as magnetic moments.

In addition to this, unlike the paper clips, the size of these grains is very small, and a square inch of the platter can store hundreds of Gigabits of data. Therefore, an electromagnet with a very small head is used to write data to these small grains. Here is how data is written on these grains using an electromagnet.

Writing Data to the Hard Drive

Let's say your computer wants to store a file on your hard drive. This data is nothing but a set of 1's and 0's, which change the direction in which current flows in the write head. Due to the current change, the electromagnet's polarity changes—inducing a different magnetic field in the platter below. It is these differences in the magnetic fields on the platter which create the different magnetic moments in the grains.

Therefore, if your system wants to store 1, the grain will have a different magnetic moment when compared to 0. These differences in the magnetic properties of grains enable hard drives to store data.

Understanding the Different Methods of Storing Data on a Platter

Humans are generating more data than ever before; in fact, more than 75 zettabytes of data were created, captured, copied, and consumed worldwide in 2021. This staggering number shows that hard drives need to store more data than ever before. To do this, the grains on platters need to be made smaller and crammed closer to one another.

Doing this creates problems as smaller grains can lose the magnetic information they possess due to environmental factors. Therefore, the magnetic moments must be aligned in different orientations to solve this problem.

Here are the different ways in which data can be stored on the platters:

  • Longitudinal Magnetic Recording: As the name suggests, Longitudinal Magnetic Recording (LMR) longitudinally stores data. What this means is that the magnetic dipoles have the same orientation as the movement of the write head—parallel to the plane of the platter. Although efficient, the size of dipoles on hard drives using LMR technology takes up a lot of space. Due to this, a density of 100 GB per square inch is offered by LMR.
  • Perpendicular Magnetic Recording: Also known as conventional magnetic recording, Perpendicular Magnetic Recording (PMR) offers more storage when compared to LMR. The reason for this increase is the difference in the orientation of magnetic dipoles. You see, in LMR, data is stored longitudinally, but with PMR technology, the dipoles are aligned perpendicularly. Therefore, the dipoles on a PMR drive are perpendicular to the movement of the write head. This change in orientation increases the information density as each dipole takes lesser space when compared to dipoles used in LMR technology. Due to this, a density of 300-400GB per square inch is offered by PMR.
    Perpendicular Recording on magnetic hard drive
    Image Credit: Pierre Gronau/Wikimedia
  • Shingled Magnetic Recording: As explained earlier, data on a hard drive is stored in grains. These data-storing grains are placed in circular tracks on the hard drive. It is on these tracks that the write head moves to store information. Although these tracks are placed close to each other in PMR and LMR technologies, they are not made to overlap as it causes issues when reading the data. That said, SMR overlaps the tracks on the hard drive to increase the amount of data that can be stored on a drive. As these overlapping tracks look like the shingles on a rooftop, this technology was named Shingled Magnetic Recording. Due to the overlapping, SMR increases storage density by 25 percent.
  • Heat-Assisted Magnetic Recording: Although the shift from LMR to PMR led to a substantial increase in the amount of data that could be stored on a hard drive, it was still not enough for companies like Google, Facebook, Microsoft, and Amazon, which store at least 1,200 petabytes of information. Therefore, to further increase hard drive information density, Heat Assisted Magnetic Recording (HAMR) came into the picture. This technology heats the platter using lasers so that grains can be placed closer to one another and the information they store is not lost due to environmental factors. Due to this improvement, hard drives using HAMR can store over two terabytes of data in a square inch.

In addition to the alignment of the dipoles, how your drive is partitioned will also affect its performance (and yes, there is an optimum partition method to maximize performance).

Reading Data From Hard Drives

Now that we understand how data is written to hard drives, we can look at how the hard drive can read the written data.

You see, the grains on the hard drive are lined up into a set of tracks. It is on these tracks that the information is stored. When you store a file on your computer, the write head writes in a section of this track, and the hard drive remembers the file's location.

Track on a hard drive
Image credits: Heron2/Wikimedia Commons

When you open the file, the CPU asks the hard drive to do the same. The hard drive moves the arm to the same track where the data was written.

It is here that the read head comes into the picture. Just like the write head uses an electromagnet to write data, the read head uses a Giant Magneto-Resistive (GMR) head. However, unlike the write head, which induces magnetic fields, the GMR detects changes in magnetic fields on the platter. Due to these properties of the read head, it can read data from the platter.

It is this reading and writing of data that makes your hard drive noisy.

Are Hard Drives Still Worth Buying?

Solid-state drives have taken the world by storm, offering faster read/write speeds. That said, this speed comes at a price, and finding cheap SSDs with high storage capacities is no easy task.

Therefore, if you have a huge gaming library that expands over several terabytes, it's best to get a mechanical hard drive that can store all that data without burning a hole in your pocket.