What is a hard disk drive?(HDD)

A computer hard disk drive (HDD) is a non-volatile data storage device. Non-volatile refers to storage devices that maintain stored data when turned off. All computers need a storage device, and HDDs are just one example of a type of storage device.

HDDs are usually installed inside desktop computers, mobile devices, consumer electronics and enterprise storage arrays in data centers. They can store operating systems, software programs and other files using magnetic disks.

More specifically, hard disk drives control the reading and writing of the hard disk that provides data storage. HDDs are used either as the primary or secondary storage device in a computer. They 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 (SCS cable, among other formats. The HDD is also connected to a power supply unit and can keep stored data while powered down.

A hard disk drive — often shortened to hard drive — and hard disk are not the same things, but they are packaged as a unit and either term can refer to the whole unit.

Why do computers need hard disks?

Storage devices like hard disks are needed to install operating systems, programs and additional storage devices, and to save documents. Without devices like HDDs that can retain data after they have been turned off, computer users would not be able to store programs or save files or documents to their computers. This is why every computer needs at least one storage device to permanently hold data as long as it is needed.

How do hard disk drives work?

Most basic hard drives consist of several disk platters — a circular disk made of either aluminum, glass or ceramic — that are positioned around a spindle inside a sealed chamber. The platter spins with a motor that is connected to the spindle. The chamber also includes the read/write heads that magnetically record information to and from tracks on the platters using a magnetic head. The disks also have a thin magnetic coating on them.

The motor spins the platters at up to 15,000 rotations per minute. As the platters spin, a second motor controls the position of the read and write heads that magnetically record and read information on each platter.

WHAT IS SSD

HDD and SSD Explained

The traditional spinning hard drive is the basic non-volatile storage on a computer. That is, information on it doesn’t “go away” when you turn off the system, unlike data stored in RAM. A hard drive is essentially a metal platter with a magnetic coating that stores your data, whether weather reports from the last century, a high-definition copy of the original Star Wars trilogy, or your digital music collection. A read/write head on an arm accesses the data while the platters are spinning.

An SSD performs the same basic function as a hard drive, but data is instead stored on interconnected flash-memory chips that retain the data even when there’s no power flowing through them. These flash chips (often dubbed “NAND”) are of a different type than the kind used in USB thumb drives, and are typically faster and more reliable. SSDs are consequently more expensive than USB thumb drives of the same capacities.

Like thumb drives, though, SSDs are often much smaller than HDDs and therefore offer manufacturers more flexibility in designing a PC. While they can take the place of traditional 2.5-inch or 3.5-inch hard drive bays, they can also be installed in a PCI Express expansion slot or even be mounted directly on the motherboard, a configuration that’s now common in high-end laptops and all-in-ones. (These board-mounted SSDs use a form factor known as M.2.