Inside your Hard Disk Drive

A hard disk drive contains a number of internal disks, called platters, which are coated with a delicate magnetic substance. These platters spin at high speeds under a mechanical arm (the actuator arm) that moves backwards and forwards over the surface of each platter.

On the end of this metallic arm is a small copper wire (read & write head). The computer sends a pulse through this wire - which changes the state of the magnetic surface of a platter as it passes underneath. In this way the files that you store on your computer are encoded into the magnetic substance.

Hard disk disks are very complex. They have a circuit board and a number of moving parts. In terms of data recovery, the first thing that you must evaluate is whether it is a hardware problem that is stopping you from accessing your data. Common hardware problems include a faulty circuit board or problems with the actuator arm

Hard Disk Drives can and do Fail:

Your hard disk drive is composed of one or more spinning platters containing tracks of magnetically stored information. The platters are read by delicate read-write heads that hover over the surface of the disk on a cushion of air created by the speed of the platter's rotation. This air gap (cushion) is about 2 to 15 microns. By contrast, a smoke particle or fingerprint is about 30 microns in size. The read-write heads are attached to a Voice Coil actuator armature that can move the head assembly over the surface of the disk.

Platters: Most platters or disks are made of an aluminium alloy, but ceramic or glass platters have also been used. The diameter of the Platters in Inches can be 21/2, 31/2 or 51/4, and the thickness of the media can be from less than 1mm to about 3mm. The platters are coated on both sides wit a magnetic material. Recent hard drives apply the magnetic layer by plating a thin metal film onto the surface through galvanization or sputtering. These surfaces have a shiny chrome-like appearance.

The whole assembly moves incredibly fast. The magnetic platters rotate at either 4800, 5400, 7,200, 10,000 and now as fast as 15,000 (rpm) revolutions per minute, and the movement of the read/write heads to separate areas of the disk is almost instantaneous.

Head Actuators: The head assembly actuator is an analogue system, with the exact amount of head movement controlled by the exact amount of current applied. The actual position of the coil is determined by servo (or indexing) information, which is written to the drive by the manufacturer. The location of the heads over the tracks on the platters is adjusted to different tracks by reading and reacting to this information. The access speed of typical voice coil actuator drives is between 10 and 20 milliseconds.

Preamplifier circuitry: From inside the HDD sealed assembly, there are data and control wires for the spindle, the head actuator motors, and to the read-write heads themselves. This ribbon cable (from the heads) typically has a low-level preamplifier chip placed inside a sealed assembly. This chip takes pulses from the heads (as close to the source as possible) and cleans up and amplifies these signals before transmission to the electronics outside of the sealed housing.

Air Filtering and Ventilation: Minor wear of internal components and occasional contact of the heads with the surface can cause microscopic particles to be loosened within the HDA. A permanent air filter is mounted within the hard drive air stream to remove most particles before they can cause damage to delicate mechanisms. Most drives also have a small vent to allow for minor air exchange from outside of the housing. This allows for equalization of air pressure so drives can be used in different environments without risk of imploding or exploding (humidity changes).

Hard disks will fail eventually because they are mechanical devices, and as such, wear out. It's as simple as that. The most likely reason for a drive to fail before its time, however, is physical shock damage. If a drive is bumped or jostled while it is active (meaning that the read-write heads are busy reading or writing data on the surface of the platters) there is a chance that the heads will make contact with the surface of the platter, which can cause all sorts of problems.

This 'head-crash' can cause damage both to the read heads and the surface of the platter; can knock the read-heads out of proper alignment, and more besides.
Fortunately, modern drives are well protected against this kind of damage while the heads are in motion. All hard drives manufactured in the last decade or so protect themselves automatically when the drive spins down by parking the read-write heads, or lowering them onto a safe area on the surface of the stopped platter.

Protection Measures Against Hard Disk Crashes:

With the advancement of technology, platters manufactured today are guarded with anti-vibration mechanism and head parking technology to prevent the head from making contact with the rotating platter when a drive is shocked. Protective layers are also implemented on the magnetic surfaces of newer disks to withstand a certain amount of head crash abuse before permanent damage sets in. For instance, laptops computer hard disk are manufactured with better shock resistance capability as these machines are typically on the move. However it is always recommended to avoid moving your computer while the disk is still in operation.

A non-powered hard drive is difficult to damage by physical means. For this reason, you should avoid moving your computer around while it is powered on. Laptop hard disks are usually better protected than standard desktop hard drives, but they can still be affected by physical shocks.

The electric motor that powers the platter's rotation is also subject to failure over a long period of use. A failure in the drive's motor or bearings can cause slow performance or data read/write errors due to the platters spinning up slowly or rotating at an incorrect speed.