How hard drive works - read before you open!

F or all those to whom convinced that for them - "the sea is knee-deep". We present you the coolest visual animation of hard drive that made by Jacob O’Neal creative director Animagraffs. We hope that now, you will have less desire to check the «internals» of your drive unnecessarily! And we assure you that the experience of opening a failed hard drive will be equivalent to that you can do with this interactive hard drive model - but without the risk of losing important information for you!

Hard drive structure

Here is the Seagate ST4000DM000 (ST4000VN000-1H4168) hard drive, model of 2012, of the Lombard family. Equipped with 4 aluminum plates and 8 heads. Carrier layer made using PMR (CMR) technology 6th generation Showa Denko


VCM rotary drive

Connection interface (SATA/SAS)

Electronics board (PCB)

Pack of discs (plates)

Magnetic head (read / write)

Spindle motor

Reading and writing information

Permanent Magnets (Neodymium)

Each permanent magnet has a “north” and “south” pole, where the north attracts the south and vice versa.

Voice coil

An electric current passing through the voice coil creates an electromagnetic field that interacts with permanent magnets. Depending on the direction of current flow, the polarity of the electromagnetic field also changes, which drives the coil. The intensity and duration of the current determines how fast and far the coil will travel.

The speed of movement of the coil allows you to deliver the heads from the external track of the plate to the internal (full stroke) more than 50 times per second!

Flexible Printed Circuit

Connects the electronics board to the VCM rotary actuator and the head switch (preamp).

Suspension milli DSA

With a slider and a loop installed, it is called HGA. Improves head positioning with a PTZ drive.

Magnetic heads

Elements are located vertically relative to the magnetic surface of the plates, closer to the end of the slider. And separated by thin film barrier layers.

Plate surface


The slider surface facing the disk has etched special shapes, aerodynamic grooves. Which stabilize the flight height of the slider. The rotation of the plates creates an “air bearing”, which holds the head at a height of ~ 2 nm above the plate. And for a more accurate positioning of the read/write elements, a thermal drive is used.

Reading head

The read head is a TMR sensor (tunnel magnetoresistance sensor), consisting of an insulator sandwiched between two layers of ferromagnetic material (free layer/contact layer).

The magnetization vector of the contact layer is fixed, and the vector of the free layer changes in accordance with the direction of the “read” magnetic field of the domain. If these vectors coincide, the passage (tunneling) of electrons through the insulator to the free layer is possible and the total loop resistance decreases. When they are opposite, the passage of electrons through the contact layer is difficult and, therefore, the loop resistance increases.

Recording head

In perpendicular magnetic recording, the field generated between the pole cut of the recording head and the reflective layer (“Soft magnetic underlayer”) located under the working layer of the plate is used. Which amplifies and reflects the generated field to the return pole of the writing head. Thus magnetizing the domains of the working layer ("Hard magnetic layer") of the plate.   The magnetic domain with the north pole up is 1, while the domain with the north pole down is 0.

Magnetic domain

Any magnetic material consists of domains - regions within which the magnetic moments of all atoms are directed in one direction. Under the action of an external magnetic field, domains can change the direction of the magnetic moment. Typically, a domain consists of 60-80 magnetic grains, which equates to 1 bit.

Recording on plates (disc pack)

Contrary to popular belief, recording on magnetic plates does not occur simultaneously. The sequence and size of the recorded area, for each head, will depend on the quality of the plates and heads, the volume of the model and firmware. And another type of file system. So this moment, let’s leave it on the conscience of manufacturers. For example, we took a formatted disk and recorded several files on it, and then using the PC3000, we built a map of the occupied space and entered it into this table.

For greater clarity, the recording process, we suggest you play a magnetic snake. The numbering and sequence of cells is equal to the sequence and head number when recording. The game is displayed only, on laptops and computers!

StartScore: 0Press the start button to begin.

Plates and spindle motor

Platters clamp

Rigidly fixes the assembled package of plates. Not allowing them to move relative to each other.


At the moment, there are two types of plates for hard drives:

Plates with an aluminum substrate
- have the widest application because of their cost and weight. The largest aluminum plate supplier is the corporation Showa Denko. In January 2019, the company announced 9th generation PMR (CMR) traditional magnetic plate technology.

Glass backing plates
- although they have higher performance (lower thickness and weight, heat resistance, energy efficiency and, most importantly, uniformity of the working surface). Only now reached the 3.5" drives.
The largest supplier of glass plates for hard drives is the corporation Hoya. Back in September 2017, it's company presented images of 3.5" discs with a package of 10 (0.5mm) and 12 (0.381mm) plates.And in February 2019, the corporation announced the start of the construction of a platinum factory for 2.5" discs, as well as discs using MAMR and HAMR technologies.

Spacer rings

Spacer rings are located between the plates and are made with high precision (non-magnetic alloy or polymers) to ensure the best alignment of the plates.

Hydrodynamic (liquid) bearing (FDB)

The spindle shaft is located inside the sealed chamber of the bearing housing, densely filled with a homogeneous viscous fluid. Which fills the space between the shaft and the housing and prevents their contact. This reduces the coefficient of friction and wear, noise and heat. And also increases vibration resistance.


A permanent magnet is attached to the inside of the moving spindle, which is part of a brushless DC motor (BLDC). Most hard drives rotate the plates at 5,400 (90 Hz), 5,900 (98 Hz), 7,200 (120 Hz), 10,000 (166 Hz) or 15,000 (250 Hz) RPMs (revolutions per minute).

Layer structure

Lubricant layer

The uppermost layer of the plate is a polymer lubricant PFPE perfluoropolyether (PFPE), 1-2nm thick. Which minimizes friction between the protective layer and the heads (read / write).

Protective layer

Made of carbon diamond-like coating (DLC) to ensure corrosion resistance and protection of the magnetic recording layer (Magnetic data layer). The thickness of the protective layer is ~ 3-5nm.

Magnetic data layer

Modern PMR environments are called exchange-conjugated composite (ECC) environments. Which implies multi-layering in the formation of both the working magnetic layer (hard magnetic layer) and the orienting sublayer (soft magnetic underlayer). Which, in turn, can be supplemented with other layers to improve performance.
«Hard magnetic layer» – determines the thermal stability of the medium and serves as a carrier layer of information. Structure: CoCrPt, CoCrPtSiO2, CoCrTa, Co-PdSiO, CoPd, FePt.
«Intermediate layer» – usually embedded between hard-hard or hard-soft magnetic layers. Used to obtain the desired crystallographic texture. Structure: Ru, Ta, SiO2, RuCr.
«Seed layer» – mainly used to increase the crystalline orientation and grain size. Structure: Ta, TaRu, Ru, CrTi.
«Soft magnetic underlayer» – responsible for the orientation of the domains in the working layer. It is also called a reflective layer. Structure: Сo, CoFe, CoNi, FeSiO, CoTaZr, FeCoB.


The backing plate is made of non-magnetic material and is usually made of aluminum (0.635, 0.8, 1.0, 1.27, 1.5 and 1.8 mm), glass (0.381, 0.5 and 0.63 mm) or other ceramic materials .
Next, the so-called “Adhensive” (“Interlayer” or “Sublayer”) layer is deposited on the substrate, with a thickness of ~ 10-40 nm. Most are made of an alloy of nickel phosphorus (NiP) for aluminum and nickel tantalum (NiTa, Ti or Ta) for glass / ceramic substrates. For leveling the surface and improving adhesion, as well as preventing the influence of the substrate on subsequent thin-film layers.

Connection interface (SATA/SAS)

Typically, 3.5" drives have SATA (user/corporate) or SAS (server) interfaces for connecting. When both 2.5" and 1.8" drives have acquired: USB3.2, Type-C, SFF-8784, ZIF, LIF, etc.

Electronics board (PCB)

The main components of the hard drive control are concentrated on the electronics board: System on a Chip (SoC), power management controller (responsible for VCM, SM, SoC and Preamp), RV sensors that cache RAM memory chips (HDD - SDRAM or SSHD - SDRAM + NAND ) and a ROM chip - containing the boot part of the code (individual for each disk).

Recirculation filters/Breather hall

Inside the hermozone zone, special recirculation filters are installed. The purpose of which is to prevent contamination of the surfaces of magnetic heads and plates. Catching the smallest particles of materials, the friction of which, when operating a hard disk, can lead to their formation!
In drives that do not use helium as a filling of the hermozone zone, there are special holes (breather hall) that are closed on the inside with filters (made of coal or silica gel). Their presence prevents the ingress of dust, fumes and moisture.

Air circulation

The air flow naturally circulates inside the hermozone zone as the plates rotate. While the opening (breather hall) provides equalization of internal pressure with air pressure outside the disk hermozone zone.

Useful links and materials used

Ismail Beigi Research Group - Manufacture and materials for hard drives (ENG)
HABR | IBM - IBM offers a new way of super-dense recording of information: 1 bit to 1 atom (ENG) - Spintronics, types of magnetic materials, GMR and TMR. (ENG)
ISFT 2015 - 4th International Symposium Future of Technology and Science 2015 (ENG|PDF) - 29th Magnetic Recording Conference (TMRC 2018) (ENG|PDF) - 28th Magnetic Recording Conference (TMRC 2017) (ENG|PDF) - TDK Pioneers Mastering TMR Heads - Mathematical calculation of the possible use of a 3-head drive - Optimization of suspension and bracket materials (ENG|TH|PDF) - Designing Adaptive Analog Filters for Magnetic Read Input Channels 2015 (ENG|PDF) - The use of thin-film FePt layers with HAMR technology (in the examples there is a PMR layer structure on a glass substrate) (ENG) - Visual inspection technology in the hard drive industry (ENG) - What is a DLC? (ENG) - High temperature resistant soft magnetic underlayer for high density PMR (ENG) - Simulation of contact of the magnetic head with the surface at the time of recording (ENG) - Perpendicular magnetic recording (ENG) - Thin Film Reference (ENG) - Functionality of thin-film layers perpendicular to magnetic recording (ENG) - Effect of SiO2 Content on CoCrPt (ENG) - Interchangeable Composite (ECC) Media (ENG) - Technical means of information technology (RU) - Brief Encyclopedia of Magnetic and Superconducting Materials (ENG) - Advances in data storage: the prospect of materials (ENG) - Using CoTaZr as a Soft magnetic layer (ENG) - Magnetic nanomaterials: fundamentals, synthesis and application (ENG) - Using RuCr as an intermediate layer (ENG) - Nanostructure media development for PMR (ENG|PDF) - Magnetic materials, processes and devices 10 - Extremely high density ultra-thin carbon fiber magnetic recording (ENG) - Адсорбент для дисковых накопителей (фильтрация) (ENG) - Adsorbent for disk drives (filtering) (ENG) - Manufacturer of multilayer thin-film TMR / GMR elements - chemical composition (EN) - FDB bearing HMF type (ENG|PDF) - FDB ROF type bearing (ENG|PDF) - Spindle motor device for 2.5 "drives (ENG) - Production of cases and covers for hdd (ENG) - Lubricant layer (ENG) - Production Quality Control Devices HDD (ENG) - Production Quality Control Devices HDD (ENG) - Lubricant layer (ENG) - Aluminum Plate Production Process Showa Denko - Manufacturers of glass / ceramic substrates (ENG) - Equipment for the deposition of thin-film layers and the production of glass / ceramic plates for hard drives (ENG) - Equipment for quality control of plate manufacturing (ENG) - Production of body parts and head brackets (Actuator Pivot Flex Circuit Assembly) (Video) (ENG) и product list (ENG) - The process of grinding and polishing magnetic heads (ENG)
The process of cleaning the aluminum substrate NiP 2018 (JP) - Methods of control in the manufacture of glass plates (ENG) - Processed aluminum plate supplier (ENG) - Cleaning agents for polished substrates (ENG) - DSA head suspension (ENG) - Exploring HGA mounting materials for the main bracket (ENG|PDF) - HGA and HSA assembly process (ENG) - SSA suspension assembly diagram (ENG) - Examples of CLA and DSA (PTZ) suspensions, covers, etc. (ENG) - SSA and DSA Suspension Comparison (PZT) (ENG|PDF)mirror - DSA Suspension (PTZ) - Study on the need for blanking rings in APFA (Actuator Pivot Flex Assembly) (ENG|PDF) - Build Quality Control Device APFA - Micro pendant DSA (PZT) - What HSA (Head Stack Assembly) and HGA (Head Gimbal Assembly) (ENG) - General production of heads (ENG) - Suspension head work (ENG) - Loopback or Trace Gimbal (TG) technology in action! (ENG) - Slider flight control (Triple-stage actuator) or DSA (PTZ) vs DSA (PTZ) + Termal actuator (thermal drive) + Thin-film voice coil (ENG) - Factory equipment supplier for the assembly and production of storage devices (ENG) - Design, assembly and automation of assembly lines - an assembly line with a list of equipment is very detailed (ENG) - HDD assembly factory equipment supplier (ENG) - The production process of the plates, the composition of the layers is described. (ENG) - Hard Disk Drive Full-Cycle Equipment Manufacturer (ENG) - Manufacturer of lubricants, filters, polishers and quality control systems for the production of hard drives (ENG) - The process of manufacturing aluminum plates (ENG) - How Western Digital makes hard drives