AI overview
A hard disk is a device inside a computer that stores all your files, programs, and operating system by recording data on spinning magnetic disks. It matters because without it, your computer would have nowhere to save your work or keep the software it needs to run.
AI-generated from the Wikipedia summary — may contain errors.
Article
Hitachi 500GB 3.5" drive, 2011, opened to show the disk platters and read/write arm
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical computer data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box, possibly in a disk enclosure for portability. Modern disks do not have removable media, in contrast to the disk drives common in the 1960s and 1970s.