The Hard Disk (Fix Disk) is an industry of high technology and precision which gathering the semiconductor, laser optics, precision machinery, higher physics, and chemical technology. There are many surrounding products of personal computer can be manufactured in different countries, but only CPU and Hard Drive can be made in the United States and Japan. Owing to the industry structure of HDD is related to the advanced technology, the crucial techniques have been strictly controlled in the United States for disclosure.
The principle of HDD storage is using the control circuit of Read/Write head to change the magnetic polarity (+,-) on the surface of the media. In order to store more data in the media, the magnetic has to be made extremely small (just like the sensitization particles in the film), and then coating it on the surface of media with very high density. To allow head speedy moving back and forth on the surface of media, it needs to“float”on the top of the media but won't touch it. However, the reading signal will become weak if the head is floating too high, and it will not be able to fulfill the need of high capacity hard disks. It is necessary to lower the flying height of head to about 0.5 uin similar to a 747 airliner needs to keep at least 1 inch flying height above the ground but will not cause crash. Therefore, the surface of media must be kept smoothly; any particle or dust will easily cause read/write head scratch the magnetic surface of media (limited lower than 1% of hair diameter) to permanently damage to the data. This is the reason why all the processing of data recovery is required to be taken only inside the uncontaminated Class 100 Clean Room.
The four parts of HDD including: Media, Read/Write Head, Spindle Motor & Voice Coil Motor, Base & PCBA.
The substrate of media is made of metal or glass. To achieve quality of high density & high stability, the surface of it has to be very smooth without any defects. The skill is to coat the magnetic particles on the substrate of media and then cover the lubricant on the top. There are two high-tech procedures occur here: 1. To produce tiny magnetic particles without impurities. 2. To coat the magnetic particles evenly.
Using a 3.5" media as an example, the inner diameter is 25 mm . But the actual diameter should be around 20mm after deduction of outer and inner circle that does not store data. The media stores date by principle of magnetic polarity (+,-).
A magnetic particle equals to one bit.. Therefore,
8Bit=1 Byte
1Mb=1024 x 1024=1,048,576 Bytes
1GB=1,048,576 x 1,024=1,073,741,824 Bytes
100GB=107,374,182,400 Bytes x 8Bits =858,993,459,200 Bits
(One bit records 0 & 1 polarity. 8 Bits record one character such as A,B,C….)
The density of each side of the media is very high. To protect the Media from contamination, all the data recovery process can only be taken inside the Class 100 Clean Room. The media is completely blank and with no any signal on it when it is first made in the factory. It will be encoded with Servo Track Write when the HDD manufacturers proceed the assembling.
The multiple read/write heads (up heads and down heads) are fixed on the same set of Actuator Arm. The heads will move together with whole set of the Arm at the same time. The read/write principle of HDD is based on the vertical recording, for example, when a data of 10MB is being stored, the first head writes 4,096 Bytes(depends on specification), the second head writes 4,096 Bytes and so on. Therefore, a file is being stored by several sections on each media as well as the process of reading .Multiple read/write heads could achieve high speed requirement, however, there are more advanced techniques available now.
The perpendicularity of heads cannot have any deviation (limited to 0.001% diameter of a hair) since the heads have to move back to the original position precisely without shaking even the Arm moves back and forth with high speed .The heads and medias can not be loose or declination, otherwise the track will not be on regular. The current technologies still unable to adjust the deviated heads or medias back to the original position. Since it has to take 3D graph to observe points X & Y as well as the perpendicular point of each head. Besides, the difference between outer and inner diameter also has to be taken into consideration. This is reason why the hard drives afraid of being collided and even the heads can't be replaced freely.
There are on or more medias set on the Spindle Motor which runs with speed of 7,200 or 10,000 RPM (revolution per minute). The bearing (ball type or liquid state) quality is strictly required to avoid shaking but keep balance of the media. It needs to be able to sustain 24H x 365 days of continuous operation without grinding or bearing noise.
The HDD is assembled in the following order: To fix Spindle Motor, Media, Voice Coil Motor, and Head, then check if the Fly Height value of heads is qualified or not (should be around 0.5 uin).
The head can speedy moving within each track because the head is floating on the media without touching it. However, the signal will be too weak if the head is floating too high. On the contrary, the surface of media will be scratched if the head is floating too low. Therefore, the surface of media must be very smooth to avoid any particle or dust cause permanent damage to the data. The serious condition of it just like car tire crashed by big stone on high speed driving. Therefore, any HDD assembling or data recovery process should only be taken in a high-purified Clean Room and the install procedure should be accomplished by laser equipment instead of labor.
The HDD won't be usable after assembling since the media still has no any sector exists. The HDD can be readable only after head's embedding Servo in circle on Media through specific Servo Track Writer by each manufacturer.
100GB=107,374,182,400 Bytes/512 Bytes=209,715,200 Sectors.
The Servo Write is controlled by laser without any deviation. The amount of sectors of inner diameter is lesser than that of the outer diameter since the media is made by round shape. This is the most
difficult technique called Zone Bit Recording coding method.
The hard drive will be usable after Embedded Servo is completed. The head can stay on the track regularly, and the BIOS can detect the specifications such as the values of Cylinder, Head, and Sector while the computer is power on. Finally, the BIOS will send the Controller over to the operation system, the user can store the data after create new partition and make format.
Summary ﹕
In order to protect media from contamination, all the HDD taking apart process can only be taken inside the Clean Room.
Head and media are part of each other. When they have been assembled, the perpendicular Embedded Servo on each side of the media by Servo Track Writer will also be done accordingly. No deviation is permitted since the head will not be able to locate normally even due to slight crash .Therefore, it is impossible to take apart head or media to put on another hard drive even if its model is the same.
The Media, magnetic medium, is similar to the cassette tape which is only allowed one polarity. Once the electric current goes through the head, the original polarity value will be easily changed. Therefore, a damaged hard drive will be overwritten and destroy the original data by careless operation.
