A hard disk drive (HDD) is a type of non-volatile computer storage device that stores digitally encoded data on rapidly rotating platters with magnetic surfaces. At its core, a hard drive consists of one or more rigid (“hard”) platters coated with magnetic material. The platters are paired with magnetic heads that read/write data to the platter surfaces. The platters are spun at high speeds by a spindle motor. An actuator arm with read/write heads moves across the platters to access data. All of these components are sealed inside a protective enclosure. The basic components that make up a hard drive include the platters, read/write heads, spindle motor, voice coil motor, and controller board. Hard drives allow computers to store vast amounts of data, far more than its semiconductor-based solid state drive counterpart. They form a key component of modern computers.
Hard Drive Platters
The platters inside a hard drive are the disks that actually store data. Platters are made from non-magnetic materials like aluminum, glass, or ceramic because these non-magnetic materials don’t interfere with data reading and writing (Dataloss, 2017).
The most common platter material is aluminum. Aluminum platters provide a good combination of low cost, rigidity, and light weight. Glass platters are heavier but provide even more rigidity. Ceramic platters are also very rigid, but are more expensive (Engineering Stack Exchange, 2015).
Whatever the platter material, it is coated with a very thin layer of magnetic material, usually 10-20 nanometers thick. This magnetic coating is where the data is actually stored in the form of magnetic polarities – positive or negative (north pole or south pole). The read/write heads float just above the magnetic coating on the platters to magnetically record data.
Common Magnetic Coatings
The coating is one of the most crucial components of a hard drive platter. This thin layer of magnetic material stores all the data bits through the orientation of magnetic poles. The most common magnetic coatings are:
- Cobalt-alloy: Most modern hard drives use a cobalt-based alloy such as cobalt-nickel, cobalt-chromium, or cobalt-platinum for the platter coating. Cobalt provides high magnetization and thermal stability which allows for high data density recording. The alloying elements enhance corrosion resistance and mechanical durability.
- Platinum-alloy: Some drives use a platinum-alloy coating, usually platinum-cobalt or platinum-chromium. The platinum enhances the magnetic and mechanical properties. However, platinum alloys are more expensive than cobalt alloys.
The specific composition and structure of the magnetic coating has a major impact on the drive’s storage density, thermal stability, head-disk interface, and reliability. Extensive engineering goes into optimizing and evolving these alloys for continued improvements in HDD technology.
Read/Write Heads
The read/write heads are responsible for reading and writing data onto the platters. They are attached to the end of the actuator arm and float just above the disk surface.
Heads are typically made of ferrite or ceramic materials. Ferrite heads are made of a ceramic compound with iron oxide, while ceramic heads are made from aluminum oxide and titanium carbide.
The heads have an electromagnetic coil wound around a core. When writing data, an electric current flows through the coils, which magnetizes the core. This magnetic field imprints magnetic transitions onto the disk surface representing the binary 1s and 0s of data.
During reading, the magnetic transitions on the platter induce a magnetic field around the head. This magnetic field produces an alternating electric current in the coil, which is decoded into 1s and 0s by the drive electronics.
Voice Coil Motor
The voice coil motor (VCM) is made up of copper windings wound around steel. The copper windings are attached to an actuator arm and work with the magnets to move the read/write heads back and forth rapidly and precisely across the spinning disks (CFTC, 2023). This allows the heads to access data anywhere on the disks (CFTC, 2023). The VCM converts electric currents into the mechanical motion needed to position the heads using the principle of electromagnetism. The rapid and accurate movement enabled by the VCM is critical for hard drives to deliver fast data access speeds.
Spindle Motor
The spindle motor is responsible for spinning the hard drive platters at a constant speed. It contains a series of strong permanent magnets typically made of neodymium or samarium-cobalt alloys. As per the research, “the magnetic hard disk drive (HDD) is based on a rotating disk driven by a spindle motor” (Gao 2023). The magnets interact with the motor’s stator coils to rotate the spindle and disks at speeds up to 15,000 rpm in desktop hard drives and 10,000 rpm in enterprise models.
The strong magnetic field generated by the spindle motor magnets also stabilizes the platters while they spin at high speeds. Precise rotation and stability are critical to allow the read/write heads to accurately access data stored on the platter surfaces.
Base Casting
The base casting of a hard drive provides a protective outer casing for the internal components. It is made of either an aluminum or magnesium alloy, which offers rigidity to maintain structural integrity while also being lightweight.
Aluminum alloys, like 6061 or 7075 grades, are commonly used for hard drive casings. Magnesium alloys are sometimes used as well for their stiffness, strength, and low density. The base casting frames and supports the internal components.
The base casting is designed to allow proper airflow and cooling across the platters and heads during operation. It has an opening to allow access for the read/write heads to make contact with the disks. The casting tightly houses the spindle motor which rotates the disks, and the actuator that moves the heads.
Overall, the metal alloy base casing plays a crucial role in protecting sensitive internal parts from damage while allowing the drive to function properly.
Sources:
[1] https://en.wikipedia.org/wiki/Hard_disk_drive_platter
Circuit Board
The circuit board in a hard drive is a thin printed board that contains copper traces and solder (Professional Plastics, 2022). It serves as the main control hub, connecting all of the drive’s internal components together. The board contains the interface connections for power and data transfer, as well as a built-in controller chip that manages the flow of data to and from the drive platters (PCB Sky, 2022). The solder and copper traces connect the controller chip to the drive’s motors, read/write heads, and other electronics.
Hard drive circuit boards are very precisely manufactured with many thin layers of copper separated by insulating material. The copper layers are etched to create the conductive traces between components, while holes plated with copper form connections between layers. High density surface mount components like memory chips and capacitors are soldered to the board. Overall, the design of the circuit board allows all the drive’s components to communicate efficiently.
Conclusion
In summary, the key metals and materials found in hard drives include:
– Aluminum or glass platters coated with magnetic materials like cobalt-alloy or ferrite
– Copper alloy or ceramic read/write heads
– Motors containing copper wires and neodymium magnets
– Aluminum, stainless steel or magnesium for the base casting
– Gold, copper and tin traces on the circuit board
While hard drives contain small amounts of precious metals, the primary materials are aluminum, glass and various magnetic alloys. Proper recycling can recover these metals for reuse in new electronics.
References
Hard drives use a variety of materials and components to store data magnetically. The key component is the platter, which is coated with a thin magnetic film to enable data recording. Common magnetic coatings include:
- Cobalt-based alloys like CoCrPt and CoPtCr
- Iron, nickel and chromium alloys like NiFe and CoNiCr
Other key components include the read/write heads, voice coil motor, spindle motor, base casting and circuit board. These work together to enable the hard drive to read and write data as the platters spin.
Sources:
- Magnetic Storage Systems and Devices. Ch 13 in Electrical Engineering Handbook edited by Wai Kai Chen. CRC Press, 1993.
- Advances in Magnetic Data Storage Technologies. Mee and Daniel, IEEE Transactions on Magnetics, v.26, n.6, 1990.
- Hard Disk Drive Mechatronics and Control. Guoxiao and Tong, CRC Press, 2016.