How Hard Drives Work

Hard disk drives (HDDs) are a cost-friendly and durable storage option. With capacities up to 2 TB or more, they offer ample storage for media files, backups and heavier workloads. They’re also very reliable. But compared to solid-state drives, HDDs have slow read/write speeds that can impact overall system performance.

HDDs have platter-like objects called “disks,” which are magnetically sensitive and where data is stored using an electrical charge from a precise actuator arm. The arm is guided to specific spots on the platters using a motor that spins them at pre-set rates, often measured in revolutions per minute (RPM). Each platter is divided into concentric circles with logical units called sectors that are assigned unique addresses that are read as either 0s or 1s by the drive’s read/write head.

Each platter has thousands of sectors that can each accept an electric charge. The resulting pattern is translated into the binary data that represents bits of information (ones and zeroes). A typical sector on an HDD has around 100 bits. Early HDDs used longitudinal recording to store data on the platters, which aligned the sector locations horizontally, but it caused problems as the size of sectors decreased, so they would flip their charges randomly based on temperature. Newer HDDs use a technique called “perpendicular” recording to create more space on platters.

While they still have an advantage over SSDs, mechanical failures are a concern with hard drives due to their moving parts. If the platters or actuator arm get jostled, they can skip or fail. HDDs are also a little heavier and consume more power than SSDs. However, a technology called helium is available to help keep the drive cool, light and quiet, which can improve longevity and performance.