harddisks

A hard disk drive (HDD) is a data storage device that uses magnetically coated rotating platters to store digital information. Data is written and read by magnetic heads that move across the surfaces on an actuator arm while the platters spin at a constant speed. Information is organized into tracks and sectors. HDDs provide large storage capacity at a relatively low cost per gigabyte and are commonly used for bulk storage, backups, and archival purposes.

A typical HDD comprises one or more circular platters, a spindle motor, read/write heads, an actuator assembly, a cache, and an interface connector. Performance is described by rotational speed (RPM), seek time, and sustained transfer rate. Consumer drives commonly spin at 5400 or 7200 RPM; enterprise models may run at 10,000 or 15,000 RPM. Interfaces include SATA and SAS, with higher-end systems sometimes using Fibre Channel. Form factors are mainly 3.5 inches for desktops and 2.5 inches for laptops and mobile racks.

Technological evolution has advanced data density through perpendicular magnetic recording and, more recently, technologies such as shingled magnetic recording and 4Kn/512e sector formats to improve capacity and compatibility. Modern drives can include caches ranging from a few megabytes to several tens of megabytes. Reliability is often described by MTBF and annualized failure rate, and many drives provide SMART monitoring for health status.

Compared with solid-state drives, HDDs offer lower cost per gigabyte and higher raw capacity but slower random access and higher power consumption. They remain a staple for bulk storage, long-term archival, and applications where large capacity at a lower price is prioritized, while SSDs are favored for speed and latency-sensitive tasks.