what is hdd

A hard disk drive (HDD) is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. HDDs are a type of non-volatile storage, retaining stored data when powered off. All computers need hard disk drives for storage, and they are used either as the primary or secondary storage device in a computer. HDDs are commonly found in the drive bay and are connected to the motherboard via an Advanced Technology Attachment (ATA), Serial ATA, parallel ATA or Small Computer System Interface (SCSI) cable, among other formats. A typical HDD design consists of a spindle that holds flat circular disks, called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminum alloy, glass, or ceramic, and are coated with a shallow layer of magnetic material typically 10–20 nm in depth, with an outer layer of carbon for protection. HDDs are slower, larger, and less expensive than solid-state drives (SSDs), but they offer more storage capacity and easier data recovery if damaged.