Hard Disk Drives (HDDs)

Details about the design and operation of hard disk drives

Possibly the PC component with the greatest variety of types and styles is the storage device.  Unsurprisingly, storage devices contain all of the data that we, as users, enter into a computer system, keeping it there until we need to access, edit or update it at a later stage.

Storage devices come in a number of flavours and, while they all carry out the same function, they do so in different ways depending upon their design.

Hard Drives (also known as Hard Disk Drives or HDD for short) are a type of storage device that read from and write to a hard disk.  Although the terms Hard Drive, Hard Disk and Hard Disk Drive are often used interchangeably or referred to as the same component, they are not the same thing.  The hard disk itself is made up of several plastic or metal platters with a magnetic coating on it’s surface and is contained within the HDD. The Hard Disk Drive, however, contains the Hard Disk and provides part of the interface for a computer to access the information contained on the disk.

A 2.5 inch SATA Hard Disk Drive


In the vast majority of modern day computer systems, the HDD also houses a Disk Controller.  The Disk Controller is the circuitry that enables the computer system to communicate with the Hard Disk.  Rarely, in older systems, the disk controller may be mounted separately to the HDD on an expansion card.

HDD’s are versatile components.  They can be mounted internally on the computer chassis and through a set of direct connections to the system board or externally through connection via an expansion card or a port.  In either case, the HDD must have at least one power cable connection and data cable connection in order for the computer system to access it.

In order to be able to read the information contained on a hard disk, it must be spun for the data to be accessed.  There are various speeds at which the hard disks may be spun at and these are recognised as Revolutions Per Minute (rpm).  Common hard disk speeds include (but aren’t limited to) 5,400 rpm, 7,200 rpm and 10,000 rpm.

Although it is possible to encounter other legacy types of hard drive technology. The most common type, by far, that is currently used within computer systems is the Serial Advanced Technology Attachment (SATA) drive.  SATA drives support one device per channel and hot swapping (meaning that the drive can be replaced without powering down the computer system).

A disassembled HDD
Study Reference Disclaimer. 

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