As we know, the quality of optical drive mainly has two aspects, namely, error correction performance and stability. Technically speaking, there are two main technologies to ensure these two indicators: tracking and focusing. Before we know about tracking, let's take a look at the data storage method of CD. Unlike the concentric track mode of hard disk, optical disk stores data in continuous spiral tracks. The size and density of each region of its orbit are the same, which can ensure the more reasonable distribution of data storage space. Because of this, the laser head can't seek like a hard disk head. In order to ensure that the laser head can track accurately, the "tracking" technology is produced, which makes the optical head always aim at the track of the spiral track. If the laser beam coincides with the track of the optical disc, the deviation at this time is "0". But in most cases, it is impossible to achieve such an ideal state, and there will always be some deviations when tracking, so the optical drive needs to be adjusted. If the tracking range is not large enough, the data CD may not be readable and the CD may not sound. This is what we usually call poor error correction performance.
Focusing means that the laser beam can accurately shoot on the track of the optical disc and get the strongest signal. When the laser beam returns from the optical disk, it needs to pass through four photodiodes, and the signals emitted by each photodiode need to be superimposed to form a focus error signal. Only when the output of this error signal is zero can the focusing be accurate. If the focus is not accurate, it is obviously impossible to read the CD smoothly.
The current hard disk, whether IDE or SCSI, adopts Winchester technology, which has the following characteristics:
1。 Sealing of magnetic head, magnetic disk and moving mechanism.
2。 The surface of the fixed and high-speed rotating plating plate is flat and smooth.
3。 The radial movement of the magnetic head on the disk.
4。 The magnetic head is in contact with the disk when it starts and stops, but it is in flight and does not directly contact the disk when it works.
Disc: Hard disk disc is made of aluminum alloy (new materials are also useful for glass) with magnetic powder attached to its surface. These magnetic powders
Divided into several concentric circles is called trajectory, and there seem to be countless small trajectories arranged randomly on each concentric circle.
Magnets, representing the states of 0 and 1 respectively. When these small magnets are influenced by the magnetic force from the magnetic head, they are arranged.
The direction will also change. Using the magnetic force of the magnetic head to control the direction of some designated small magnets, so that each small magnet can be used for
Store information.
Disk body: the disk body of a hard disk is composed of multiple disks stacked together and placed in a sealed box. They are mainly
Driven by the shaft motor, it rotates at high speed, and the speed per minute reaches 3600, 4500, 5400, 7200 or even more.
Head: The head of a hard disk is used to read or modify the state of magnetic substances on the disk. Generally speaking, every magnetic surface will
There is a magnetic head, starting from the top and numbering from 0. When the head stops working, it contacts the disk, but
At work, it is flying. The magnetic head starts and stops contact in the landing zone of the disk, and the landing zone does not store any numbers.
It is reported that there is no problem of damaging any data when the magnetic head starts and stops in this area. When reading data, the disk rotates at high speed because
The movement of the magnetic head adopts exquisite aerodynamic design. At this time, the head is 0.2-0.5 micron high from the data area on the disk surface.
The degree of "flying state". Neither contact with the disk surface causes wear, but also can read data.
Motor: The motors in the hard disk are all brushless motors. With the support of high-speed bearings, the mechanical wear is small and they can work continuously for a long time.
Work. The high-speed rotating disk has obvious gyro effect, so it is not advisable to move the hard disk at work, otherwise it will aggravate the rotating shaft.
The amount of work undertaken. Hard disk head seek servo motor mostly adopts voice coil rotation or linear motion stepping motor for feed.
Accurately track the track of the disk under the adjustment of service tracking, so the hard disk should not collide and collide when working, and it should be very small when moving.
Relax.
Speaking of principles, is everyone clear?
First of all, there is no contact between the head and the data area, so there is no wear problem.
Secondly, as soon as the hard disk is turned on, the rotation speed of the spindle motor can reach 4500 or 7200 rpm, which
Whether you use FLASHGET or ED, as long as you turn it on, they will turn. Their clothes are also very soft.
There is nothing to do.
Thirdly, the head moves back and forth from left to right under the control of the seek motor, with a small amplitude, starting from the innermost part of the disc.
The landing zone begins, slowly moves to the outermost layer, then slowly moves back, and one track goes to another to find it.
Looking for data. There won't be any big jumps (not frogs). So its wear can also be ignored.
So how did the heat come from?
The first is the rotation of spindle motor and servo motor, which is the main reason for the temperature of hard disk.
Secondly, the friction between the high-speed rotating disk and the air. This is also the main factor.
And hard disk reading and writing?
Unfortunately, its calorific value can be ignored! ! ! ! ! ! ! ! ! !
Hard disk reading operation is that the change of magnetic field on the disk affects the resistance value of the magnetic head. In this process, the disk will not generate heat and magnetism.
The head is a little hot because of the change of current. What about the write operation? On the other hand, through the magnetic head
The current intensity changes constantly, which affects the magnetic field on the disk. This process is magnetic because of electromagnetic induction.
High heat. But the disk itself will not heat up, because the permanent magnets on the disk are cold and will not change because of the magnetic field.
It will be converted into heat.
But in general, the calorific value of magnetic head is dwarfed by the former two.
Heat can be conducted by radiation, so high heat will not harm the permanent magnets on the disk? Actually, the damage is very small.
Yes, under normal circumstances, the temperature of permanent magnet degaussing is much higher than that of hard disk. Of course, if your chassis cools down,
No, it's nobody's fault.
I have to say some people's mistakes here:
One. High temperature affects the resistance induction sensitivity of the magnetic head, so reading and writing errors will occur, which has nothing to do with the permanent magnet.
Two. The so-called thermal expansion will not shorten the distance between the disk and the magnetic head, because the flight of the magnetic head is an aerodynamic principle.
Under normal circumstances, always keep a certain distance from the CD. Of course, if you hit the hard disk hard, then this vibration ......
Three. The so-called seek means that the hard disk moves from the initial position to the specified track. The so-called reset action does not happen often.
. Because the physical location of the track is stored in CMOS, the hard disk does not need to move back to track 0 and start over. as long as
As soon as the magnetic head is started, the so-called reset action is completed. The reset operation will not be sent again unless the computer is restarted.
Healthy.
Four. The disk structure of IDE hard disk and SCSI hard disk is similar. It's just that the interface bandwidth of SCSI hard disk is higher than that of contemporary ID.
E hard disk is bigger, often SCSI cards often have something similar to CPU to slow down the occupancy rate of the main CPU. Only this
This is why Seagate will use its SCSI hard disk technology on IDE hard disks.
Five. Hard disk reading and writing are sectors based on cylinders. Cylindrical surface, that is, the radius of all magnetic surfaces in the whole disk is the same.
Concentric tracks, which divide each track into several areas, are called sectors. Hard disk write operation is to write one first.
A sector, and then write to the next sector of the same cylinder, the head will not move to another until one cylinder is completely filled.
On the track. Therefore, the file storage on the hard disk is not continuous (from
Users watch it together, but from the bottom of the operating system, its storage is not continuous). So FLASHGET is still
No matter how many threads ED opens, the seek of the magnetic head is generally not bigger than playing games and listening to songs. Of course, this situation
It's just a simple download or upload, but in fact, in this process, who can guarantee that they will not start other requirements?
Software for reading and writing hard disk? Maybe many people like to play games or listen to songs while downloading. Not to mention WINDOWS.
It is necessary to read and write virtual memory files frequently. So, download it with FG or ED, and the hard disk will torture peace.
It won't be too bad compared with then.
Six. Let's talk about why it's not good to open too many threads in FLASHGET, and why ED reads and writes hard disks frequently. First of all, there are more threads.
, the cpu utilization rate is high, and the page change action is frequent, so the virtual memory reads and writes frequently. As for why, I have learned to do the problem.
Anyone who works on system principles should know it, so I won't talk about it here. Where does ED download files from several people at the same time?
Several people download your files at the same time, similar to FG multithreading. So the hard disk light flashed. But now,
Our hard disk is cached, and the data is not written to the hard disk immediately, but stored in the cache first, and then stored to a certain extent.
Measure it and write it to the hard disk once. No matter how it is set in FG, it is actually written into the cache first. But this
The process also needs CPU intervention, so the setting time is too short and the CPU utilization rate is high, so the hard disk light is still flashing.
Because virtual files are read and written.
Seven. Hard disk is frequently read and written, and the head arm moves frequently under the drive of seek servo motor, but this is a loss for machinery.
Although there is, it is actually not big. Unless your hard disk itself has mechanical problems such as arm deformation (parallel imports are the most common reason)
Obstacles). The real wear and tear lies in the head. Changing current will cause it to age, but compared with its life. .....
. It should also be within a reasonable range. Unless the head hits the disk because of vibration.
Eight. Mechanical circuits are most seriously affected by high temperature, especially the circuit board outside the hard disk and the integrated block above it.
It will accelerate aging at high temperature. So one of IBM's glass hard drives, although it has bad tracks, uses some software, Ma.
It disappeared on the floor. If it is more serious, it will be normal to change the circuit board. That's the reason.
I'm really tired after typing so many words.
In short, the hard disk will affect its service life because of poor environment and improper maintenance, but it is definitely not the fault of the software.
FLASHGET, ED, FTP, although they often read and write hard disks, they are not as fun as you.
Generally speaking, listening to music in the theater is harmful to the hard disk. More specifically, their so-called wear and tear on the hard disk can be ignored.
Don't worry just because you see the hard disk light flashing. Otherwise, those servers that provide WEB services and FTP services,
Their hard disk can read and write, which is by no means an ordinary game, and the hard disk loaded with software is no different.
The hard disk has a parameter called continuous trouble-free time. Refers to the longest time from the start of hard disk operation to failure.
Bit is hour, and the abbreviation is MTBF. Generally, the MTBF of a hard disk is at least 30,000 or 40,000 hours. The specific situation can be seen.
Parameter description of the hard disk manufacturer. This continuous trouble-free time, you can divide it yourself and see how many years it is. however
Think for yourself, how long does your hard disk work continuously?
At present, the machine I use has been turned on continuously 1 year, except that it is turned off several times in the middle of ten minutes to clean up the dust.
Never stopped (using gold to 6 generations of 40G). There are also three servers that use SCSI hard disks, which have been useless for two consecutive years.
Yes, it has stopped. The calorific value of hard disk is by no means comparable to that of ordinary IDE hard disk (10000 rpm hard disk).
I think I have a say in this.
Finally, add a few points:
One. It is best not to buy parallel imports or repaired hard disks. Parallel imports are very unsafe in transportation, although on the surface.
There seems to be no damage, but the mechanical body may be damaged due to various factors during transportation. Repair the goods.
Not to mention. To tell the truth, those who complain that the hard disk is easy to damage, you'd better look at your hard disk first.
Whether it's true or not.
Two. The working environment of the hard disk needs to be neat, and special attention should be paid not to use it in an environment with frequent power cuts and a lot of dust.
Hard drive. The chassis should be cleaned once every month or two.
Three. Hard disk machinery is most afraid of vibration and high temperature. Therefore, the environment should be better, especially the chassis should be firm to avoid an earthquake. electric current
Don't stagger the brain tables.
Four. Always tidy up the hard disk. Here is a misunderstanding of most people. Most people think that hard disk fragmentation will become more and more difficult.
Disk wear, actually, is not the case. The increase of hard disk fragmentation itself will only make the hard disk read and write less time than fragmentation.
It's just a lot of waiting, and the loss of hard disk can be ignored (I'm just talking about the fact that the servers on the network at present,
The operating system they use most is UNIX, but there is no defragmentation software under UNIX. Even Microsoft
NT4, itself is not). However, due to the frequent movement of the magnetic head, the reading and writing time increases, so the CPU
Page-changing actions will be more frequent, leading to frequent reading and writing of virtual files (in fact, the accurate statement here is page-changing files)
, thus increasing the hard disk head seek load. This is the disadvantage of hard disk fragmentation.
Five. Try to avoid sudden power failure, cold start and other things that increase CPU load (such as playing games) when reading and writing hard disks.
Listening to songs while playing, or playing large 3D games while downloading), these are more harmful to the hard disk than most people think. origin
Because I won't talk about it, typing is too tired.
In short, as long as you pay attention to using the hard disk, the hard disk will not say goodbye to us so soon. Of course, if it's difficult.
The quality of the CD itself is not good, so I have nothing to say.
1. Hard disk reading and writing principle
The working principle of hard disk can be divided into two aspects: reading (reading data from hard disk) and writing (writing data into hard disk). For hard disk, whether reading or writing, you need to issue commands to access data. So as long as the CPU receives the read-write command of the system program, the CPU begins to issue commands to the memory and hard disk.
In the reading part, the CPU will first give the command to write data, and then the memory will send the data to the hard disk through the bus. After the central coordination of the motherboard I/O chip (the control chip responsible for transmitting digital data, that is, the South Bridge chip), the data will be sent to the buffer area of the hard disk in turn (that is, the cache of the hard disk), and finally the data in the central area will be recorded to the disk by the hard disk control circuit (at this time, a series of mechanical parts in the hard disk will be carried out).
In the writing part, the CPU also gives the command to read data first, and the I/O chip on the motherboard starts to coordinate in the center, then the hard disk control chip starts to read data into the buffer, and finally the data in the hard disk buffer is sent to the memory through the bus on the motherboard to complete the operation of reading hard disk data.
Therefore, the two storage locations of data are hard disk and memory respectively; Among them, the data will be temporarily stored in the buffer and transmitted with the bus; Of course, all operations, except the commands issued by the CPU, can only be realized by the commands of the I/O chip on the motherboard and the hard disk control circuit.
2. Physical storage principle of hard disk
The hard disk uses the hard disk as the recording medium, and the disk is magnetized into countless magnetic fields by the tiny current of the magnetic head to store data. The most commonly used materials are aluminum alloy, chromium alloy and other materials, and IBM has also introduced hard disks made of glass. At present, IDE, SATA and SCSI interface hard disks all adopt Winchester technology, which has the following characteristics: 1. The magnetic head, magnetic disk and moving mechanism are sealed; 2. The surface of the fixed and high-speed rotating plating plate is flat and smooth; 3. The magnetic head moves along the radial direction of the disk. The magnetic head is in contact with the disk when it starts and stops, but it is in flight state and does not directly contact the disk when it works.
(1) CD
Hard disk platter is to attach magnetic powder to the surface of the platter. These magnetic particles are divided into several concentric circles, called tracks. On each concentric orbit, it seems that there are countless small magnets arranged randomly, representing the states of 0 and L respectively. When these small magnets are influenced by the magnetic force from the magnetic head, their arrangement direction will change accordingly. Using the magnetic force of the magnetic head to control the direction of some designated small magnets, so that each small magnet can be used to store information.
(2) Tray body
The disk body of a hard disk consists of multiple disks, which are stacked together and placed in a sealed box. Driven by the spindle motor, they rotate at high speed, with the rotating speeds of 3600 rpm, 4500 rpm, 5400 rpm, 7200 rpm, 65438 rpm +00000 rpm or 65438 rpm +05000 rpm.
(3) magnetic head
The head of a hard disk is used to read or modify the state of magnetic substances on the disk. Generally speaking, each magnetic surface will have a magnetic head, starting from the top and numbering from 0. The magnetic head is in contact with the disk when it stops working, but it is in flight when it works. The magnetic head starts and stops in the landing area of the disk in a contact manner, and the landing area does not store any data, so the magnetic head starts and stops in this area, and there is no problem of damaging any data. When reading data, the disk rotates at high speed. Due to the ingenious aerodynamic design of the head movement, the head is in a "flying state", with a height of 0.2-0.5 micron from the data area of the disk. Contact with the disk surface will not cause wear, and data can be read reliably.
(4) Motor
The motors in the hard disk are all brushless motors, which can work continuously for a long time with little mechanical wear under the support of high-speed bearings. The high-speed rotating disk has obvious gyro effect, so the hard disk in work should not be moved, otherwise it will increase the workload of the bearing. The seek servo motor of hard disk head mostly adopts voice coil rotation or linear motion stepping motor, which accurately tracks the track of the disk under the adjustment of servo tracking, so there should be no impact and collision when the hard disk works, and it should be handled with care.
1956, an engineering team of IBM showed the world the first disk storage system Ramac. Winchester technology was put forward in 1968, and the hard disk has gone through 50 years. Although hard disk technology has made a lot of progress, it has also spawned many different forms, such as SCSI, IDE, SATA, etc., just need to develop different interfaces to adapt to new applications. The structure of hard disk still does not exceed the definition of Winchester technology: sealed, fixed, high-speed rotating plated disk, the magnetic head moves along the radial direction of the disk, and the magnetic head floats above the high-speed rotating disk without contacting the disk.
A hard disk basically consists of a control circuit board and a disk body:
The control circuit board consists of interface, DSP processor, ROM, cache, head drive circuit and disk motor drive circuit. The interface includes a power interface, a data interface, a disk motor interface and a magnetic head interface inside the hard disk, wherein the power interface provides the current required for the hard disk to work, the data interface provides a channel for exchanging data with the computer, the disk motor interface provides the current required for the disk motor to rotate, and the magnetic head interface is used for providing the signal connection from the circuit board to the magnetic head and the voice coil motor; DSP processor is used to control signal and data conversion, coding and other operations; Some programs of hard disk initialization operation are stored in ROM, and some are independent chips (maybe EPROM, Flash, etc. ), and some of them are integrated in DSP. Cache is used to temporarily store the data exchanged between the disk body and the interface, so as to solve the difference between the interface speed and the internal reading and writing speed of the hard disk. The size of the cache has a certain impact on the data transfer rate of the hard disk. With the continuous development of hard disk, the capacity of cache is also increasing. The magnetic head driving circuit is responsible for driving the magnetic head to accurately position and shaping and amplifying the magnetic head signal. The motor drive circuit is responsible for accurately controlling the rotation speed of the optical disc.
The disk body consists of a disk cavity, an upper cover, a disk motor, a disk, a magnetic head, a voice coil motor and other auxiliary components. In order to ensure the normal operation of the hard disk, the cleanliness of the disk body is very high. In order to prevent dust from entering, the tray body is in a relatively sealed state. Because the hard disk will generate heat during operation, in order to ensure the balance between the air pressure in the disk cavity and the outside world, there are breathing holes on the disk body, and a small air filter is installed in the breathing holes. Hard disks with different designs have different vent positions and structures. At the same time, because the servo information will be written to the disk after assembly, there is a servo information writing entry on the disk. In the dust-free workshop of the factory, special writing equipment is inserted into the disk to write servo information, which will be sealed with aluminum foil after writing.
Generally, the disc cavity is made of aluminum alloy casting. Other parts of the disk body are directly or indirectly installed on the disk cavity, and there are screw holes in the disk cavity to install the hard disk to other equipment.
The upper cover is generally made of aluminum alloy or soft magnetic metal materials, some of which are single-layer and some are bonded by multi-layer materials; Its main function is to form a relatively sealed whole with the intervertebral disc cavity, which is basically connected with the intervertebral disc cavity through screws. In order to ensure sealing, the joint surface between the upper cover and the disc cavity is generally provided with a gasket.
The main function of the CD motor is to drive the CD to rotate. Under the control of the disc motor driver chip on the control circuit board, the disc motor drives the disc to rotate at a set speed, and the rotation speed of the disc motor is increased from less than 4000 rpm to 10000 rpm, or even 15000 rpm. The increase of disk speed directly determines the seek time of hard disk; Of course, while increasing the speed, the heat, vibration and noise of the hard disk will also affect the stable work of the hard disk, so some new technologies are constantly applied to the disk motor, from the initial ball bearing motor to the current liquid bearing motor.
The platter of hard disk is one of the core components of hard disk, and different hard disks may have different platters. All data are stored on the disk, which is made by coating thin layers of magnetic materials, protective materials, lubricating materials and other different functions on aluminum alloy or glass substrate. The physical properties of magnetic materials and the structure of magnetic layers directly affect the storage density and stability of data. In order to improve the storage density and prevent the occurrence of superparamagnetic effect, various related institutions have done a lot of research work to continuously improve the physical properties and structure of the magnetosphere. The recording mode of magnetic recording layer has also developed from the previous longitudinal magnetic recording to the current vertical magnetic recording. Before the hard disk leaves the factory, servo information will be written on the disk, and the disk surface of the hard disk will be divided into concentric circles, called tracks. The tracks in the same position of multiple disks form a concentric cylinder, which is the cylinder of the hard disk. Each track is divided into sectors with the same storage capacity as the smallest unit for storing data. In order to make the hard disk work normally, the hard disk must have corresponding initialization and management programs, some of which are written into a specific area of the disk, which is often called the firmware area. For different hard disks, the physical location of this area is different, and the number and functions of recorded programs are also different. Because the complete consistency of the whole disk cannot be guaranteed in the production process, there are bound to be a few sectors that cannot read and write data stably, which is what we call bad tracks. Every hard disk should be tested for aging before leaving the factory, and the location of bad tracks should be written into the factory bad track table (p-List) in the firmware area of the hard disk. At the same time, during the use of the hard disk, there may be a few sectors that cannot read and write data correctly for various reasons, and the positions of these bad tracks can also be written into the G-List in the firmware area of the hard disk.
Magnetic head is also the core component of hard disk, and its performance has a great influence on the data storage density and internal transmission rate of hard disk. The first application of magnetic head is ferromagnetic material. 1979 invented the thin film magnetic head, which made it possible to further reduce the volume, increase the capacity and improve the reading and writing speed of the hard disk. In the late 1980s, IBM developed MR magnetoresistive head, and later developed GMR giant magnetoresistive head. Nowadays, all hard disks use GMR heads, which use the resistance value of special materials to follow the magnetic field. The magnetic head does not contact with the disk in the working process, but flies on the disk at a very low height under the aerodynamic force driven by the high-speed rotation of the disk. In order to improve the sensitivity of the magnetic head, the flying height of the magnetic head is decreasing. Usually, the magnetic head consists of a metal head arm, a voice coil motor coil and a preamplifier circuit. Driven by the voice coil motor, the magnetic head moves back and forth according to the need of reading and writing data, and locates the track where the data is located.
Because the magnetic head needs to fly by aerodynamic force driven by disk rotation, the magnetic head can't fly when the hard disk doesn't work or the rotation speed of the disk motor doesn't reach the predetermined value, and the read-write surface and disk of the magnetic head are very smooth. If they are in direct contact, adhesion will inevitably occur, which will hinder the rotation of the disk or cause damage to the head and disk. Therefore, the magnetic head needs to be parked outside the data area when it is not working. Hard disk can meet this requirement in two ways: the first way is to open an annular head parking area inside the disk, where the head is parked when it is not working. In order to prevent adhesion, the parking area is specially processed into an area with certain roughness, so that there is some air between the head and the disk when the head is parked here, but this will inevitably lead to serious friction between the head and the disk when the hard disk is started and stopped, thus damaging the head, so the hard disk also has the index of starting and stopping times; The second way is to install a head parking rack outside the disk and park it on the parking rack when the head is not working, so that the head will never touch the surface of the disk under normal circumstances, and there is no problem of starting and stopping times.
In order to prevent accidents when the hard disk is not working, different hard disks are also designed with different head locking mechanisms. When the hard disk does not work or the disk does not reach the predetermined speed, the head locking mechanism locks the head in the parking position. Some netizens reported that there was noise when the hard disk was shaking, which was caused by the head locking mechanism. In order to prevent the magnetic head from hitting the spindle of the disk motor or moving out of the disk or parking rack due to accidents, a head limit device is also designed.
Voice coil motor consists of one or two magnets with high magnetic field strength and peripheral magnetic steel, as well as a closed magnetic field and a voice coil motor coil. Under the control of the head driving circuit, the head is driven to reciprocate above the disk according to the requirements of reading and writing data, so that the head is located on the required data track.
After the hard disk is powered on, DSP first runs the program in ROM. Some hard disks check the integrity of all components, and then the disk motor starts to rotate. When the rotational speed reaches the predetermined rotational speed, the magnetic head starts to move to locate the firmware area of the disk and read the firmware program and bad track table of the hard disk. The physical location of the firmware area on the hard disk is uncertain, which is completely determined by the design of the hard disk. At the same time, not all firmware must be written on disk. Of all the firmware of the hard disk, only the password of the hard disk must be written into its firmware area. Some hard disks will first compare the serial number stored in the ROM with the serial number on the disk. If not, the hard disk will terminate the initialization work. If the key sectors or files of the firmware are damaged, the hard disk may be hit, which cannot be recognized by the BIOS or recognized as an error. When all necessary firmware is read out normally, the head will be positioned to the 0 cylinder, 0 head, 1 sector of the hard disk, which is often called 0 track. Generally speaking, the 0 head of the hard disk is located near the bottom of the disk motor, that is, the hard disk, and the 0 track is close to the edge of the disk, and then we can operate the hard disk.
Respondents: gogo 1 102- magician level 410-2516: 41.
A hard disk basically consists of a control circuit board and a disk body:
The control circuit board consists of interface, DSP processor, ROM, cache, head drive circuit and disk motor drive circuit. The interface includes a power interface, a data interface, a disk motor interface and a magnetic head interface inside the hard disk, wherein the power interface provides the current required for the hard disk to work, the data interface provides a channel for exchanging data with the computer, the disk motor interface provides the current required for the disk motor to rotate, and the magnetic head interface is used for providing the signal connection from the circuit board to the magnetic head and the voice coil motor; DSP processor is used to control signal and data conversion, coding and other operations; Some programs of hard disk initialization operation are stored in ROM, and some are independent chips (maybe EPROM, Flash, etc. ), and some of them are integrated in DSP. Cache is used to temporarily store the data exchanged between the disk body and the interface, so as to solve the difference between the interface speed and the internal reading and writing speed of the hard disk. The size of the cache has a certain impact on the data transfer rate of the hard disk. With the continuous development of hard disk, the capacity of cache is also increasing. The magnetic head driving circuit is responsible for driving the magnetic head to accurately position and shaping and amplifying the magnetic head signal. The motor drive circuit is responsible for accurately controlling the rotation speed of the optical disc.