Hard Disk Drives – Types, Sizes and Future Technology

December 21, 2018 at 1:54 pm by SEM

What is a Hard Disk Drive?

A Hard Disk Drive (Commonly referred to as a hard drive or HDD) is a device that stores digital data. It includes rigid platters made from aluminum alloy or glass coated with a magnetic material and housed within a metal case. The data is encoded magnetically and floats on a cushion of air above the platters, to put it simply.

The Many Forms of HDDs

HDDs come in various shapes and sizes. The hard drive suppliers and computer industry refer to them as 1.8”, 2.5” or 3.5” form factor drives. These form factor descriptions refer to the approximate physical diameter size of the platters that are housed within the drive casing and account for over 95% of the drives in use today.

Another way to describe hard drives is by the market segment to which they are designed. You will hear the term desktop, server, enterprise (all 3.5” drives) or mobile drives (2.5” or 1.8”) as a common description.

In order to increase the capacity of data that is stored on a platter, in 2005 the technology of storing information in a longitudinal magnetic recorded (LMR) format was changed to a perpendicular magnetic recorded (PMR) mode. Virtually all new drives purchased today are PMR drives. In order for this method of recording to be accomplished, the disk areal density (known as coercivity) had to increase up to 5,000 Oersted.

Future Drive Technology

Today’s HDDs are based on magnetic media technology with read/write heads that read the stored data that resides on the internal platters. Due to the moving parts on a hard drive, they are all subject to wear and eventual failure. The good news is that most magnetic drives have built-in diagnostics to warn the user of an eventual failure. This gives the user time to back-up the data to help mitigate the loss of any data. Drives based on flash memory are also available. These drives do not have moving parts. These memory drives are particularly important in applications where the movement of the drive itself may cause a head crash and thus a catastrophic failure. They are typically much smaller in size and therefore ideal for smaller devices that require data storage.


The most commonly used hard drives in today’s computing world are the 3.5”, 2.5” and 1.8” form factor drives based on PMR Technology. They represent over 95% of the drives currently being used in the marketplace.

While industries continue to adopt SSDs as new storage devices, HDDs aren’t going away just yet. So it’s important to know not only how they work, but also how to properly dispose of them. To learn more about HDD data destruction check out some of our products here.