What is Inside a Hard Drive?
All hard drives share a basic structure and are composed of the same physical features. This is a description of the common features and how each part works in relation to the others.
All hard drives share a basic structure and are composed of the same physical features. However, not all hard drives perform the same way — the quality of the parts inside the hard drive will affect its performance. Following is a description of the common features of the hard drive and how each part works in relation to the others. Hard drives are extremely sensitive equipment and the internal workings of a hard drive should not be handled by anyone other than an experienced professional.
The platters are the actual disks inside the drive that store the magnetized data. Traditionally platters are made of a light aluminum alloy and coated with a magnetizable material such as a ferrite compound that is applied in liquid form and spun evenly across the platter or thin metal film plating that is applied to the platter through electroplating, the same way that chrome is produced. Newer technology uses glass and/or ceramic platters because they can be made thinner and also because they are more efficient at resisting heat.
The magnetic layer on the platters has tiny domains of magnetization that are oriented to store information that is transferred through the read/write heads. Most drives have at least two platters, and the larger the storage capacity of the drive, the more platters there are. Each platter is magnetized on each side, so a drive with 2 platters has 4 sides to store data.
The Spindle and Spindle Motor
The platters in a drive are separated by disk spacers and are clamped to a rotating spindle that turns all the platters in unison. The spindle motor is built right into the spindle or mounted directly below it and spins the platters at a constant set rate ranging from 3,600 to 7,200 RPM. The motor is attached to a feedback loop to ensure that it spins at precisely the speed it is supposed to.
The Read/Write Heads
The read/write heads read and write data to the platters. There is typically one head per platter side, and each head is attached to a single actuator shaft so that all the heads move in unison. When one head is over a track, all the other heads are at the same location over their respective surfaces. Typically, only one of the heads is active at a time, i.e., reading or writing data. When not in use, the heads rest on the stationary platters, but when in motion the spinning of the platters create air pressure that lifts the heads off the platters. The space between the platter and the head is so minute that even one dust particle or a fingerprint could disable the spin. This necessitates that hard drive assembly be done in a clean room. When the platters cease spinning the heads come to rest, or park, at a predetermined position on the heads, called the landing zone.
The Head Actuator
All the heads are attached to a single head actuator, or actuator arm, that moves the heads around the platters. Older hard drives used a stepper motor actuator, which moved the heads based on a motor reacting to stepper pulses. Each pulse moved the actuator over the platters in predefined steps. Stepper motor actuators are not used in modern drives because they are prone to alignment problems and are highly sensitive to heat. Modern hard drives use a voice coil actuator, which controls the movement of a coil toward or away from a permanent magnet based on the amount of current flowing through it. This guidance system is called a servo.
The platters, spindle, spindle motor, head actuator and the read/write heads are all contained in a chamber called the head disk assembly (HDA). Outside of the HDA is the logic board that controls the movements of the internal parts and controls the movement of data into and out of the drive.
Stay up to date on the latest developments in Internet terminology with a free weekly newsletter from Webopedia. Join to subscribe now.
The following facts and statistics capture the changing landscape of cloud computing and how service providers and customers are keeping up with... Read More »Facts about Computer Science: Education and Jobs
The following computer science facts and statistics provide a quick introduction to the changing trends in education and related careers. Read More »Texting & Chat Abbreviations
From A3 to ZZZ this guide lists 1,500 text message and online chat abbreviations to help you translate and understand today's texting lingo. Read More »
Learn about each of the five generations of computers and major technology developments that have led to the computing devices that we use... Read More »Computer Architecture Study Guide
Computer architecture provides an introduction to system design basics for most computer science students. Read More »Network Fundamentals Study Guide
Networking fundamentals teaches the building blocks of modern network design. Learn different types of networks, concepts, architecture and... Read More »