Hard Drives

What are hard drives?

A hard disk drive is a non-volatile memory hardware device that permanently stores and retrieves data on a computer. It is sometimes abbreviated as Hard drive, HD, or HDD. Most commonly it uses magnetic storage to store and retrieve digital information with one or more rigid rapidly rotating disks (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 all inside of an air-sealed casing.

Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile memory, which means they retain stored data even when powered off. Internal hard disks in a computer reside in a drive bay, connect to the motherboard using an ATA, SCSI, or SATA cable, and are powered by a connection to the PSU (power supply unit).

New users often confuse memory (RAM) with disk drive space. Unlike RAM memory chips a hard drive keeps all stored information even when the power is turned off. Below is a helpful diagram showing the core physical components of a standard hard drive.

Core Physical Components of a Hard Disk Drive

As can be seen in the picture above, the desktop traditional hard drive includes the following components: the head voice recoil actuator, actuator arm, read/write head, spindle, and platter. On the back of a hard drive is a circuit board called the disk controller or interface board and is what allows the hard drive to communicate with the computer.

A hard drive can be used to store any data, including pictures, music, videos, text documents, and any files created or downloaded. Also, hard drives store files for the operating system and software programs that run on the computer.

How is data read and stored on a hard drive?

Data sent to and read from the hard drive is interpreted by the disk controller, which tells the hard drive what to do and how to move the components in the drive. When the operating system needs to read or write information, it examines the hard drive's File Allocation Table (FAT) to determine file location and available write areas. Once they have been determined, the disk controller instructs the actuator to move the read/write arm and align the read/write head. Because files are often scattered throughout the platter, the head needs to move to different locations to access all information.

Hard drive read/write head diagram

N=North and S=South polarity created by the electromagnetic write head.

All information stored on a traditional hard drive, like the above example, is done magnetically. After completing the above steps, if the computer needs to read information from the hard drive, it would read the magnetic polarities on the platter. One side of the magnetic polarity is 0, and the other is 1. Reading this as binary data, the computer can understand what the data is on the platter. For the computer to write information to the platter, the read/write head aligns the magnetic polarities, writing 0's and 1's that can be read later.

The Solid State Drive (SSD) is the newest technology replacing the standard Hard Disk Drive (HDD) as the storage component. An SSD does functionally everything a hard drive does, but data is instead stored on interconnected flash memory chips that retain the data even when there's no power present. An SDD does not require any mechanical movement and is faster.

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