How does a hard drive work?

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


But have you ever thought about how your data is stored?

Well, the answer may shock you as your system’s hard drive uses magnetism to store data. Compared to a CD, this approach is more efficient. In fact, if you stacked the equivalent capacity of CDs in front of you, it would definitely come at 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 need to know how it works physically. Basically, there are disks, one on top of the other, a few millimeters apart. These discs are called platters. Polished to a high mirror shine and incredibly smooth, they can hold massive amounts of data.

Next we have the arm. Writes and reads data on the disk. It extends over the saucer and moves across it from the center to the edge, reading and writing data to the saucer through its small heads, which float just above the saucer. The arm can oscillate about 50 times per second on average domestic drives. This figure can reach thousands on many high-spec machines and those used for complex calculations.

To put things in perspective, for hard drives spinning at 5,400 RPM, the arm travels 62 miles per hour. Also, the arm is only 10 nanometers away from the platter, and it is at this distance that the arm must read and write data on the platter.

To accomplish 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 we get into hard drives, let’s understand the concepts that hard drives use to store data.

Simply put, hard drives use ferromagnetism to store all your files in seconds. But what is ferromagnetism?

Remember when you held a set of paperclips close to a magnet overnight only to find that the paperclips now act like magnets? This behavior of certain metals that acquire magnetic properties when placed close to magnets is known as ferromagnetism. This change in the properties of metals is used to store data on your hard drive.

Although the plateau on your disk looks like a mirror beneath the surface, it’s made up of trillions of grains. These granules have properties similar to the paper clips we discussed earlier and can store magnetic information when they come near a magnetic field. To store information, these grains can have two different states, and these states are known as magnetic moments.

In addition, unlike the paperclips, these granules are very small and one square centimeter of the dish 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’s how data is written on these grains using an electromagnet.

Writing data to the hard drive

Let’s say your computer wants to save a file to your hard drive. This data is nothing but a string of ones and zeros, which change the direction in which the current flows in the write head. The change in current changes the polarity of the electromagnet, creating a different magnetic field in the plate below. It is these differences in the magnetic fields on the dish that create the different magnetic moments in the grains.

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

Understanding the different methods of storing data on a dish

People are generating more data than ever before; by 2021, more than 75 zettabytes of data have been created, captured, copied and consumed worldwide. This staggering number shows that hard drives need to store more data than ever before. To do this, the grains on saucers need to be made smaller and crammed closer together.

Doing so creates problems because smaller grains can lose the magnetic information they possess due to environmental factors. Therefore, the magnetic moments have to be aligned in different directions to solve this problem.

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

  • Longitudinal magnetic recording: As the name suggests, Longitudinal Magnetic Recording (LMR) stores data longitudinally. This means that the magnetic dipoles have the same orientation as the movement of the writing head – parallel to the plane of the record. Although efficient, the size of dipoles on hard drives with LMR technology takes up a lot of space. As a result, LMR offers a density of 100 GB per square inch.
  • Perpendicular Magnetic Recording: Also known as conventional magnetic recording, Perpendicular Magnetic Recording (PMR) offers more storage space 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 information density because each dipole takes up less space compared to dipoles used in LMR technology. As a result, PMR offers a density of 300-400GB per square inch.
  • Shinled magnetic recording: As explained earlier, data on a hard drive is stored in granules. These data storage granules 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 together in PMR and LMR technologies, they are not made to overlap as this causes problems in 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. Because these overlapping tracks look like the shingles on a roof, this technology was called Shingled Magnetic Recording. Due to the overlap, SMR increases storage density by 25 percent.
  • Heat-assisted magnetic recording: While 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 not enough for companies like Google, Facebook, Microsoft and Amazon, which store at least 1,200 petabytes of data. information. Heat Assisted Magnetic Recording (HAMR) came into the picture to further increase the information density on the hard disk. This technology heats the dish using lasers so that grains can be placed closer together and the information they store is not lost to environmental factors. This improvement allows hard drives using HAMR to store more than two terabytes of data in a square inch.

In addition to dipole alignment, how your drive is partitioned also affects performance (and yes, there is an optimal partitioning method to maximize performance).

Read data from hard drives

Now that we understand how data is written to hard drives, let’s take a look at how the hard drive can read the written data.

You see, the granules on the hard drive are arranged in a series of tracks. The information is stored on these tracks. When you save a file to your computer, the write head writes into a portion of this track and the hard drive remembers the location of the file.

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

This is where the reading head comes in. Just as 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 record. These properties of the read head allow it to read data from the plate.

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 game library that expands over several terabytes, your best bet is to buy a mechanical hard drive that can store all that data without burning a hole in your pocket.

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