Hard Drive Disk
Hard drive (HDD) is a type of storage device that uses magnetic storage to store and retrieve data. It is a non-volatile storage device, meaning that it retains data even when the power is turned off. Today HDDs are still used in many systems and have capacities ranging from a few gigabytes to several terabytes.
Components
Hard drives are complex devices made up of many interdependent components. If even a single part fails, it can compromise the operation of the entire drive.
Platters
A platter is a rigid, circular disk that holds data in a hard drive. It’s typically made of aluminum or glass to endure high-speed spinning and maintain a perfectly smooth surface—any flaw could cause the drive to fail. A thin magnetic coating is applied to both sides of the platter so data can be stored and retrieved through changes in magnetic orientation. A protective carbon layer is added on top to prevent corrosion and wear.
The surface is divided into billions of tiny magnetic regions called domains, each representing a 0 or 1 depending on its orientation. Multiple platters are stacked on a central spindle to increase storage capacity. Each platter contains concentric tracks, which are further split into sectors, the smallest addressable units that typically hold 512 bytes. Groups of sectors form clusters, which are the smallest units of space the drive allocates to store files.
To fit more data into the same area, modern drives use technologies like shingled magnetic recording (SMR), which overlaps tracks like roof shingles, and heat-assisted magnetic recording (HAMR), which uses a tiny laser to heat the platter and shrink magnetic regions. These innovations allow drives to achieve much higher storage densities.