HDD

A hard disk drive (HDD) is a data storage device that uses magnetic storage on rotating platters. Data is stored magnetically on concentric tracks and sectors. HDDs have been a primary form of non-volatile storage for decades and remain widely used for bulk storage and backups.

A typical HDD contains one or more hard platters coated with magnetic material, a spindle motor to rotate them, and an actuator assembly with read/write heads that move across the surface. An electronic controller governs data transfer, seeks, and error correction. Storage is accessed through standardized interfaces. The drives organize data into tracks and sectors, with servo information to position the heads accurately.

Performance is governed by rotational speed, data density, interface bandwidth, and seek time. Common consumer drives operate at 5400 or 7200 rpm, with higher-end enterprise drives at 10,000–15,000 rpm. Typical sequential transfer rates range from tens to a few hundred megabytes per second. Access latencies are measured in milliseconds and depend on rotation speed and drive geometry.

HDDs use interfaces such as SATA or SAS; older PATA (IDE) drives are mostly obsolete. Capacities have grown from hundreds of megabytes in the 1980s to multiple terabytes per drive today. They are price-efficient for large-scale storage and backups, but slower and more sensitive to physical shocks than solid-state drives.

Reliability varies by model and workload; modern drives include SMART data and error correction, and many devices aim for multi-year lifetimes. HDDs remain common for personal desktops, servers, and data centers as a cost-effective solution for archival and backup storage, complementing faster solid-state drives.