Data recovery base – 1. HDD mystery HDD structure


Chapter 1 of the underlying data recovery
Oaks from little acorns. Data recovery is a comprehensive, involving a wide range of knowledge technology. To carry out its in-depth study and research, one must master some basic knowledge. As the structure and principles of hard work, basic computer knowledge, knowledge of the number system, but also to have a certain software tools and techniques to use.
This chapter describes the data recovery related to some basic knowledge in order to allow readers to learn in subsequent chapters lay a good foundation.
* HDD Basics
* Computer Basics
* Basics numbers
* Tools Software Description



1.1 HDD Quest
Currently storage is basically divided into magnetic storage, electricity storage and optical storage several. U disk storage and a variety of memory cards are electric, VCD, DVD optical disc, etc. are stored, and is still the most widely used magnetic storage - hard drive. In addition to the various different physical characteristics stored on the storage medium, the logical level is still based on the file system structure, the book describes the main hard disk used to store and restore the structure of ideas.
Hard drive is one of the most common external memory, is a set of mechanical, electrical, magnetic storage devices in one of the high-precision. September 1956, IBM's engineering team to show the world a first set of disk systems (IBM 350 RAMAC Random Access Method of Accounting and Control), the total capacity of the system is only 5MB, use 50 to 24 inches in diameter disk, the head can move any piece of storage area on the disc. In 1968, IBM Corporation also filed a "Winchester (Winchester)" technology, that seal, secure and high-speed rotating disk coated tablets, head along the disc radial movement, head suspended in the top of the high-speed rotation of the disc without contact with the disc. Currently, we use the hard drive is used this technology.
1.1.1 Hard disk structure
Basically the hard disk from the control board and the body of two parts.
A control circuit board
Is controlled by the interface board, DSP processor, ROM, cache, the head driving circuit and a disk motor driving circuit composed of:
* Interface includes a data interface and power connector and an internal hard disk platter motor interface, heads interfaces -
u Power Interface provides the hard work required current.
u data interface to exchange data with a computer providing a channel.
u disk platter motor rotation motor interface provides the necessary current.
u head interface is used to provide a circuit board to the signal heads and voice coil motor connections.
*DSP processor control signal and data conversion, encoding, and other operations.
*ROM of the program stored in the hard disk initialization operations, and some ROM as a separate chip ( may be EPROM , Flash , etc. ) , some of the integrated DSP in.
* Cache for Scratch body and then **** change data in order to resolve differences between the internal interface speed and hard disk read and write speeds. Cache size has some effect on the hard drive data transfer rates, with the continuous development of the hard disk, cache capacity is also increasing.
* Magnetic head drive circuit drives the magnetic head for accurate positioning and shaping the head signal amplification.
* Precise control of the motor drive circuit is responsible for the rotational speed of the disc.
2 plate body
Body cavity by the disc tray, cover, disc motor, platters, head, voice coil motors and other auxiliary components. To ensure that the hard work, the disk body cleanliness high. To prevent dust from entering the body in a relatively sealed disk state. Since the process of heating the hard work, in order to ensure equilibrium with the outside air pressure chamber plate, the plate body with breathing holes, is mounted inside the breathing hole a small air filter, the design of the hard disk type, and location of the breathing hole structure are also different. And because the plate body after assembly is completed, the servo information to be written, so there is the entrance to write servo information on the disk body, clean in the factory workshop will be dedicated servo information is written to the device write disc from this hole stretching the body, After the writing is completed, it will be sealed with aluminum foil.
(1) Pelvis
After pelvic generally machined from aluminum alloy casting, other components of the disk body are directly or indirectly mounted pelvic above, there will be installed on the hard disk cavity to the screw holes on the other devices.
(2) superstructure
Superstructure is generally made of aluminum or soft metal processing material from, some single, some are bonded together by a multi-layer material. Its main role is associated with pelvic together constitute a relatively sealed whole, are basically connected with screws and plate chamber, in order to ensure that combine face seal, cover and disc cavity generally gasket.
(3) a disk motor
The main role of the disc the disc drive motor is rotated under the control of the control circuit board in a disc motor driver chip, the disc drive motor to set the disc rotated at a speed lower than the original rotational speed of the disc motor 4000 rev / min, to today's 10,000 rev / min, and even 15,000 rpm / min, to improve the speed of the disc directly determines the disk seek time. Of course, at the same time improving the speed, hard heat, vibration, noise, etc. will have an impact on the stability of working hard. So some of the new technologies are constantly applied to the disc motor, ball bearing motor from the initial development to the present liquid bearing motors.
Disc is generally constant speed motor DC brushless motor, three-phase AC power supply. Coil around the law into delta connection, there is a star without neutral and star center line three kinds, which can be more precisely control motor speed, so that a stable disc rotation.
(4) disc
The hard disk is one of the core components, different hard disk may have a different number. All data is stored on the disc, the disc is a magnetic material on a glass substrate coated with aluminum or thin, protective layer of material a variety of different functional materials and lubricating materials processing, in which magnetic materials Structure and physical properties of the magnetic layer directly affects the stability of the data storage density and the stored data. In order to increase storage density, prevent the occurrence of superparamagnetic effect, the relevant agencies conducted a lot of research work to continuously improve the physical properties and structure of the magnetosphere magnetosphere. Magnetic recording layer is a longitudinal magnetic recording from the previous to the current development of perpendicular magnetic recording.
(5) head
Head is also a core component of the hard disk, the head has a great influence on the performance of the hard disk data storage density and internal transfer rate. Head first application of ferromagnetic material, in 1979 invented the thin-film magnetic head, so that further reduce the size of the hard disk, increase the capacity and improve the reading and writing speed as possible. The late 1980s, IBM developed the MR magnetoresistive heads, and later developed a giant magnetoresistive GMR heads. The hard drives are now using GMR heads, which uses special materials resistance value changes with the principle of magnetic fields to read the data on the disc. During operation of the magnetic head is not in contact with the disc, but the disc rotates at high speed under the action of force to drive the air at a very low altitude flying disc. In order to improve the sensitivity of the head, the head flying height is decreasing. General head with a metal head arm, voice coil motor coil and preamplifier circuit composed of a component, the head of the voice coil motor driven reciprocating done to locate the track where the data needed to read and write data.
Because the rotation disc drive heads need to rely to aerodynamic flight, the hard disk or the disk does not work on the motor speed has not reached the predetermined value, the magnetic head can not fly. The read and write heads and platters are very smooth surface, if they are in direct contact with the disc will inevitably lead to adhesions and prevent spin or cause damage to the head and the platter. To this end, parked in an area outside the data area does not work when the head needs. There are two ways to hard to meet this requirement:
* The first way is to open a disk inside the annular head parking area, the parking of the magnetic head does not work in this place, in order to prevent adhesion, the parking area is intentionally processed into a region with a certain roughness to the head anchored in place There are certain air between the head and the disk. However, this will inevitably lead to the head and the platter to start and stop the hard drive occurs when the friction serious head injury, so there will be a start and stop times of the hard targets.
* The second way is to install a disc in the head outside the parked planes, the head does not work when parked in the parking of the shelves, so under normal circumstances, and the heads never touch the disk surface, start and stop times does not exist problems.
(6) a voice coil motor
Closed magnetic coil motor and the voice coil motor coil one to two of the high magnetic field strength of the magnet and the composition of the external composition of the magnetic head drive circuit under control of a control head movement, by reading and writing data required in the disk drive head reciprocates above the head piece is positioned on the desired data track. The current flowing through the coil to control the direction of movement of the head: When the head is to be moved by the position of the coil current is large, the head deflection; when the head is close to the specified location, the coil current flows weakened or even reverse, the head starts to decelerate. In a similar manner, a magnetic head close to a specified position until the correct positioning. In the stationary state, heads are constantly revise their position in order to avoid positioning errors.
In order to prevent accidents when the hard disk is not working, different hard disk also designed different head locking mechanism, when the hard disk is not working or does not reach a predetermined speed, head locking mechanism to lock the head in a parked position, sometimes the hard drive when the hard rock There sound is emitted by the head locking mechanism.
In order to prevent accidents occur when the head disk head crash caused by work or move to the spindle motor disc / rack parked outside, is also designed with a head stopper.
Figure 1.1 shows the internal structure of a hard disk.
Figure 1.1 The structure of the internal hard disk
Data recovery base – 1. HDD mystery HDD structure 

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