parts of a hard drive.

hard disk drive.

A hard disk drive is an electro-mechanical data storage device that stores data on spinning platters, coated with a magnetic material. The platters are paired with magnetic read/write heads on a moving actuator arm that reads data from and writes data to the platters’ surfaces. Data is accessed in a random access manner. This means that individual blocks of data can be stored and retrieved in any order. 

To simplify, imagine that a hard disk is a set of stacked disks, like phonograph records. Each disk has data recorded electromagnetically in concentric circles, or tracks, on the disk. A head, similar to a phonograph arm, writes or reads the information on the tracks. Two heads, one on each side of the disk, read or write the data as the disk spins. 

Hard disks come with a rotation speed from 5,400 rpm to 15,000 rpm. 

Revolutions per minute (rpm) is a measurement of how many times the disk spins every minute. 

Most laptop and desktop PCs use hard disks that fall between 5,400 rpm and 7,200 rpm, while hard disks at higher rpm can be found in high-end workstations and enterprise servers. Disk access time is measured in milliseconds. 

The two most common forms of modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. 

Hard drives can be external or internal.

They are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables.

parts of a hard disk drive.

A typical HDD has several disks, read/write heads, a spindle motor that spins the disks, an actuator that positions the read/write head assembly across the spinning disks and a small amount of circuitry, all sealed in a metal case to protect the disks from dust.

disk platters.

A hard disk's platters are the circular, thin metal disks where 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. They spin under the power of the drive spindle motor. Platters are made either out of aluminum, glass or ceramic. They are coated in a number of layers of different materials. The most important is a magnetic layer which is only a few millionths of an inch thick. This layer is a covering of tiny magnetic grains which form microscopic areas that can be magnetized to represent 1 or demagnetized to represent  0. 1s and 0s are then translated into the information that you interact with when you use your computer: the computer’s operating system, software and all other data.

A super thin protective layer above the magnetic media guards against accidental damage and contamination by dust or other material.

the spindle.

Platters are mounted on top of each other on a central spindle. The spindle keeps the platters at a fixed distance apart from each other with enough space for the read/write arms to get to the data on the disks. The spindle is rotated by a spindle motor. The spindle speed is measured in rotations per minute (rpm) and determines how fast data can be written to and read from the hard disk. 

actuator arm.

The read and write arm, also called the actuator arm, is the part of the hard drive that reads data already stored on the platter and writes new data on the platter. The read/write arm controls the movement of the read/write heads and makes sure that the heads are in the right position based on the data that needs to be accessed or written. If there are multiple platters in the hard drive assembly, then there will be multiple arms that work simultaneously to read and write data on both sides of each disk platter surface.

actuator.

The actuator unit is a small motor that takes instructions from the drive's circuit board to control the movement of the read/write arm and supervise the transfer of data to and from the platters. It controls the positioning of the actuator arm relative to the disk platter to ensure that the read/write heads are in exactly the right place at all times. This is achieved by an electromagnet assembly, using electromagnetic attraction and repulsion to move the read/write arm in a rapid, smooth, and precise movement.

read/write heads.

As the read/write heads move across the surface of the platter, they read the magnetic surface layer of the disk and convert it into an electrical current which can then be interpreted by software in the computer. Writing data is the opposite, where an electric current is used to change the magnetic field on the required areas of the disk.

There is typically one read/write head for every platter side.

The read/write heads never touch the surface of the disk as this would cause physical damage and make the data unreadable. They float at around 3-6nm (nanometers) above the disk surface and glide over a cushion of air. 

When the device is switched off, the read/write arm moves the heads to a parked area away from the disk surface. This prevents the heads from contacting the disk surface in the event of an impact.

circuit board or PCB.

PCB is the green board on the bottom of the hard disk. It allows electricity to pass between various components, controls the functionality of the drive, and allows communication between the drive and the device it is connected to. Like the nervous system of the drive, the PCB contains microcontrollers and other electronics that control the moving arm, the spinning disk motors and the data processing activity.

other components.

Hard disks have other components that aren't central to the physical process of storing and accessing data. These include the data connector, power connector, case, and air filter.  

connectors.

Connectors on the PCB allow the hard drive to be attached to a controlling device (PC, Laptop). 

Every hard disk has two connectors, one for the power cable and the other for the data cable: 

• the power connector connects the PCB with the computer's power supply.

• the data connector connects the hard drive with a computer's motherboard and it is used for data requests from the hard drive.

Connectors are either IDE, SCSI, USB or SATA. The majority of modern hard drives use SATA connectors.

case.

A hard disk's case protects the contents from dust, dirt and airborne particulate matter, as well as holds all of the components in place.

air filter.

In order for the heads to float correctly over the surface of the platter, the air pressure inside the casing needs to be equal to the air pressure outside of the casing. To achieve this, there is a small air inlet vent which is covered by a filter to prevent tiny particles entering the casing and potentially getting onto the disk surface.

Some drives are actually vacuum sealed. These drives use helium to create the necessary space between the read/write heads and platters. The helium gas limits the chances of read/write head crashes, and since the drives are sealed, there’s little to no chance of media contamination.

what does a hard drive do.

Basically, a hard drive stores digital content or data: documents, pictures, music, videos, programs, application preferences, and operating system. 

Everything stored on a hard drive is measured in terms of its file size: megabytes (MB), gigabytes (GB), and terabytes (TB). Documents (text) are generally very small while pictures are large, music is even larger, and videos are the largest. 

A hard drive stores binary data through tiny microscopic magnetic lines drawn on a metal disk. 
As we mentioned before, a hard disk drive is composed of a spinning metal disk called a platter which is coated with a magnetic material. A read/write head has a powerful electromagnet on its tip which is capable of drawing tiny magnetically charged lines on the surface of the platter. If a line is magnetically attractive it is considered a “0”, if it is magnetically repulsive, it is considered a “1”. 

A color rendered image showing the magnetic lines on an HDD platter. The width of the photo is about 1/10 the width of a human hair.

Every desktop computer or laptop has a drive that stores all of the important data. Unfortunately, they can be at risk of data loss due to hardware failures, physical damage, and malware. 

Kotar Data Recovery has a long history of expertise with HDD data recovery. We have developed proprietary tools and techniques for recovering data from any make, model, or brand of HDD.