How Hard Disk Drives Work - Animagraffs (2023)

  • How Hard Disk Drives Work - Animagraffs (1)

Hard Disk Drives (HDDs) use spinning disks (platters) to magnetically store information.



Logic board

Platters (disks)

Read/Write heads


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Reading & writing data

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Permanent magnets

Each permanent magnet (naturally magnetic material) has a "north" and a "south" pole where north poles attract south poles and vice versa.

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Voice coil

Electricity circulated through the voice coil creates an electromagnet (a magnetic field produced by an electric current). Current flow direction through the coil changes the orientation of the north and south poles of the electromagnet, which moves the voice coil either toward or away from the north and south poles of the magnets. The intensity and duration of the current determine how quickly and how far the coil moves.

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Voice coils move fast enough to pivot the arms from the outside to the inside of the platter (full stroke) over 50 times per second!

How Hard Disk Drives Work - Animagraffs (4)


The arms are connected and pivot together.

Read-write heads

platter surface


The disk-facing surface of the slider has specific shapes etched into it that manage air flow and pressurization. As the platters spin, an air pocket or “air bearing” is created and keeps the head ~2 nm (nanometer) from each platter – thinner than a finger print.

Read heads

The read heads are TMR (tunneling magnetoresistance) devices, which consist of an insulator sandwiched between two sensitive magnetic materials

Magnetic fields from the platter influence the closest magnet, causing electrons to tunnel or travel through the insulator and flip the polarity of the second magnet — thus, "reading" the platter's varying fields without disturbing them.

Write heads

Write heads create an electromagnetic field that positions the north pole of a domain either up or down. The magnetic field is such that one side of it is much more concentrated, while the other end is more spread out. This allows the field to influence only the atoms on one side of the field (the “right side” of the field in this graphic). A magnetic domain with a north pole up could be a 1 while one with a north pole down could be a 0. Each 1 or 0 is considered a "bit" of data.

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Magnetic domain

Electrons in atoms create magnetic fields, and the direction they “spin” determines the direction of their north and south magnetic poles. Hard disk magnetic domains usually consist of about 100,000 atoms with magnetic poles oriented in the same direction.

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Multi-platter writing process

Data is written on both sides of each platter in the same respective location; if something 16 bits in size is written to or read from the platters, 2 bits would be on each of the 8 platter sides to account for the total amount.

For example, the phrase HARD DISK could be written on both sides of four platters as shown in the graphic to the left.

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Platters & spindle

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Cap & screws


Both sides of the platter can be used, with each side usually able to hold around 500 GB (gigabytes) of data for a total of 4,000 gigabytes (4 terabytes) between 4 platters.

How Hard Disk Drives Work - Animagraffs (8)

Data storage comparison

If these bits (1's and 0's) were printed on 8.5x11 paper in a 12pt font, it would be 9.6 billion pages – enough pages to fill 957,000 standard four-drawer file cabinets. These file cabinets could completely cover 65 floors of the new One World Trade Center building!

Spacer rings

Spacer rings are placed between each platter, and are precisely milled to ensure the platters and arms align properly.

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Fluid bearing

The spindle uses fluid bearings to limit friction, noise, and increase durability. The spindle shaft sits in a tight, airless, sealed chamber within the bearing housing surrounded by a thin layer of lubricant.

This lubricant fills the space around the shaft, and prevents the shaft from contacting the housing


The moving spindle has an attached permanent magnet which forms part of a basic electric motor with the stationary copper coils. Most hard drives spin the platters at 5,400 (90 hertz) or 7,200 (120 hertz) RPMs (Revolutions Per Minute).

How Hard Disk Drives Work - Animagraffs (9)

Platter composition

Lubricant layer

A 1-2 nm thick layer of lubrication prevents friction between the protective layer and read / write heads.

Protective layer

A carbon based protective layer is applied, then covered in a 1 nm thick layer of lubrication to protect the media layer of the platter. The protective layer has a smoothness of at least 0.4 nm – like a perfect circle the size of the earth with only 5.7 cm (2.3 in) of variance or imperfection.

Media layer

The media layer is made of a magnetic material, usually an alloy of Cobalt and other metals, and is about 100 atoms thick.

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The base of the platter is non-magnetic and is usually made from aluminum or glass (this layer would be many times thicker than those above if shown at full width).

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Hard drives have separate connections for the power and data cables, and a Jumper Block. The pins on the jumper block can be connected to slow data transfer rate to be compatible with older, slower hard drives.

Logic board

The logic board controls the read/write heads using a built-in map of the platters to determine which areas are available and which areas are occupied. It also controls voice coil positioning, spindle motor speed, overall power management, and the transfer of data to and from the hard drive.


A filter is placed at the edge of the platters to catch any debris created or disturbed by them. Some drives have a breath hole with an Activated Carbon filter that absorbs vapors, and prevents dust or debris from entering the drive. Newer helium drives are sealed and don’t have a breath hole.


Air is naturally circulated within the drive as the platters spin, while a breather hole allows the interior pressure to equalize with air pressure on the outside of the drive.


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How Hard Disk Drives Work - Animagraffs? ›

Current flow direction through the coil changes the orientation of the north and south poles of the electromagnet, which moves the voice coil either toward or away from the north and south poles of the magnets. The intensity and duration of the current determine how quickly and how far the coil moves.

How do hard disk drives work? ›

The hard drive contains a spinning platter with a thin magnetic coating. A "head" moves over the platter, writing 0's and 1's as tiny areas of magnetic North or South on the platter. To read the data back, the head goes to the same spot, notices the North and South spots flying by, and so deduces the stored 0's and 1's.

What is the anatomy of a hard drive? ›

The disks in a hard drive are called platters and this is where your data is stored. There are typically between 1 and 5 platters stacked on a central spindle, with data being stored on both sides of each disk. Each platter is made of either aluminium, glass or a ceramic material.

How does a hard drive store data without power? ›

Instead, data is stored on a series of NAND chips, which can retain their charge without a power source. Hard disk drives (HDDs) store data on a series of spinning magnetic disks called platters. Hovering a few nanometres above the magnetic platters are the read/write heads, located on the tip of the actuator arm.

How is data stored on a hard disk drive? ›

How is data stored on a hard disk? Data is stored on a hard drive in binary code, using 1s and 0s. The information is spread out on the magnetic layer of the disk(s) and are read or written by the read heads that 'float' above the surface thanks to the layer of air produced by the ultra fast rotation of the disk.

What are the 4 types of hard drives? ›

Types of Hard Drives – SATA, PATA, SCSI, and SSD.

What does a hard disk drive do in simple words? ›

They can store operating systems, software programs and other files using magnetic disks. More specifically, hard disk drives control the reading and writing of the hard disk that provides data storage. HDDs are used either as the primary or secondary storage device in a computer.

What breaks a hard drive? ›

Causes. There are a number of causes for hard drives to fail including: human error, hardware failure, firmware corruption, media damage, heat, water damage, power issues and mishaps.

Where is the root of a hard drive? ›

The very top of the directory tree is called the root directory. You can think of it as sitting directly on the hard drive. It can contain first-level directories, and there can be second-level directories nested inside the first-level ones.

Is the hard drive the brain? ›

HARD DRIVE = BRAIN – Subconscious All knowledge of programs, files and data is stored on the Hard Drive. Just like the brain, it is sectioned off for various purposes. The hard drive stores and retrieves all of our precious information and programs for use by use whenever we wish. Just like our long term memories.

What is the difference between a hard disk and a hard drive? ›

The term “hard drive” is actually short for “hard disk drive.” The term “hard disk” refers to the actual disks inside the drive. However, all three of these terms usually refer to the same thing. The hard disk drive definition is the place where your data is stored.

What is the difference between SSD and HDD? ›

SSDs can access, read, and write files faster than HDDs. SSDs access data electronically through 'cells' that can be written and rewritten thousands of times. HDDs utilize rotational platters and an actuator arm to access files by locating them on the platter then moving to that location to read the data.

How do the HDD and SSD work? ›

HDDs are traditional storage devices with spinning platters that read and write data. SSDs use newer technology that stores data on instantly accessible memory chips. SSDs are faster, quieter, smaller, consume less energy, and more durable.

Do hard drives need to be destroyed? ›

If it's not correctly destroyed, sensitive information could still be recovered and used (potentially by data thieves) with detrimental consequences. Before getting rid of your computer, you need to remove the data from the hard drive completely.


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