Hard disk drives (HDDs) are synonymous with data storage solutions. Many desktop computers, laptop computers and enterprise-level servers are equipped with an HDD. In recent years, solid-state drives (SSDs) have emerged as a popular alternative. But there are still countless devices that use an HDD to write and read data.

What Is an HDD?

An HDD is a type of mechanical data storage solution that leverages magnetic platters to write and read data. HDDs have been around for over a half-century. The world’s first HDD, in fact, was invented by IBM in the late 1950s. Known as the 350 disk storage, it was part of the company’s 305 RAMAC system The 350 disk storage had a maximum storage capacity of just 3.75MB. In comparison, many modern-day HDDs have a maximum storage capacity of over 1TB.

3.5-Inch vs 2.5-Inch HDDs

HDDs are available in two primary form factors: 3.5 inch and 2.5 inch. These form factors determine the type of devices with which they are used. 3.5-inch HDDs, of course, are larger than their 2.5-inch counterparts. You can typically find 3.5-inch HDDs in desktop computers and servers. 2.5-inch HDDs, on the other hand, are used in smaller devices, such as laptop computers.

How HDDs Work

Whether it’s a 3.5-inch HDD or a 2.5-inch HDD, all HDDs feature magnetic platters. If you open the outer case or shell of an HDD, you’ll see a shiny metallic platter. The platters are usually made of aluminum. While aluminum itself isn’t magnetic, the platters in HDDs are coated in a magnetic material.

The platters are designed to spin. When an HDD is writing or reading data, its platter will spin. An actuator arm will move over the platter during this process. If the HDD is writing data, the arm will create data in the form of 0s and 1s. It will add this binary code to the HDD’s platter. If the HDD is reading data, the arm will read the 0s and 1s on the HDD’s platter.

The Pitfalls of HDDs

Even though they are common, HDDs are being gradually phased out in favor of SDDs. One of the problems with HDDs is their speed. They are slower than SDDs. HDDs use a mechanical data writing and reading process. They feature an arm and platter that move during use. SDDs use a digital data writing and reading process. Without moving parts, SDDs are faster than HDDs.

HDDs are also loud. You’ll typically hear the HDD as the platter spins. SDDs, conversely, are nearly silent. Without a spinning platter, they are quieter than HDDs.