The hardware structure and working principle of internal hard disk are explained in detail.

The product label is affixed to the front of the hard drive. Mainly includes manufacturer information and product information. such as trademarks, models, serial numbers, production date, capacity, parameters and master-slave setting method.

This information is fundamental to the correct use of the hard disk. The meanings of them are described in more detail below.

Hard disk mainly by the disk body, Control circuit board and interface components, such as the composition, 1-1 see.

The disc body is a sealed cavity. The internal structure of the hard disk usually refers to the internal structure of the disk, and the control circuit board mainly includes the hard disk BIOS, the hard disk cache (i.e. cache) and the main control chip. 1-2 of what you see. The hard drive interface consists of a power outlet, a data interface, and a master, slave jumper, 1-3 see.

Figure 1-1 the appearance of the hard drive

Figure 1-2 Control circuit board

Figure 1-3 HDD Interface

The power outlet is connected to the power supply to provide power for the hard drive. The data interface is a channel for data exchange between the hard disk and the motherboard and memory. Connect using a 40-pin 40-wire (early) or 40-pin 80-wire (current) IDE interface cable.

The newly added 40 line is the signal shielding line. Used to mask crosstalk during fast and high frequency transmission of data. In the middle of the main, slave disk jumper sockets to set the main, from the hard disk, that is, set the access order of the hard drive. The setting method is usually labeled on the label outside the disc, and there are some markings on the interface, and the earlier hard disk may also be printed on the circuit board.

In addition There is a vent hole on the hard drive surface (see figure 1-1). Its role is to keep the internal pressure inside the hard drive consistent with the external atmospheric pressure. Because the disc body is sealed, the vent hole is not directly connected to the interior. But through an efficient filter and the body of the connection, to ensure that the inside of the body clean and dust-free, the use of attention do not cover it.

1.2 Internal structure of the hard drive

The internal structure of the hard disk usually refers to the internal structure of the disc.

The disk body is a sealed cavity, which is sealed with the head, disc (magnetic disc, disc) and other components. 1-4 of what you see.

Figure 1-4 Internal Drive structure

The hard disc is a hard magnetic alloy platter. Film thickness generally around 0.5mm, the diameter of the main 1.8in (1in=25.4mm), 2.5in, 3.5in and 5.25in 4 kinds, in which 2.5in and 3.5in platters are the most widely used. The speed of the disc is related to the size of the disc, taking into account the inertia and disc stability. The larger the disc, the lower the speed. Generally speaking. The speed of the 2.5in HDD is between 5 r/min~7 and R/min, 3.5in drives are between 4 and r/min~5 R/min, while the 5.25in hard disk speed is between 3 and r/min~4. With the progress of technology, now the speed of the 2.5in hard disk has reached the highest speed of r/min,3.5in hard drive has reached the highest level of r/min.

Some hard drives only have a single platter. Some hard disks have multiple discs.

These discs are mounted on the spindles of the spindle motor and are rapidly rotated with the drive of the spindle motor.

The capacity of each platter is called a single disc capacity, and the capacity of the hard disk is the sum of the total platter capacity. Early HDD because the single disk capacity is low, so. Platters are more, some even up to more than 10 pieces, modern hard disk is generally only a few pieces of the disc.

All the platters in a hard drive are all the same, otherwise the control part is too complicated.

A series of a brand is generally used on the same platter, using a different number of platters. There is a series of hard disk products with different capacities.

The complete construction of the disk body is seen in 1-5.

Figure 1-5 The complete structure of the disk body

The hard drive adopts a high precision, lightweight head drive/positioning system. Such a system allows the head to move quickly on the disk and can be positioned precisely on the track specified by the computer instruction in a very short period of time.

For now, the track density has been as high as 5 400Tpi (tracks per inch) or higher; New methods, such as squeezing (or etching) graphics, grooves, and spots on the disk as positioning and tracking markers to increase the channel density equal to the disc, are also being studied to maintain disk drive speed, high density, and high reliability , significantly increasing storage capacity.

The motor in the hard drive is a brushless motor, and the mechanical wear is very small under the support of the fast bearing and can be worked continuously for a long time.

The rapidly rotating disk body produces a noticeable gyro effect, so. It should not be moved when working hard. Otherwise, the bearing's workload will be added. To quickly store and read information, the hard drive has a small head mass and inertia, so the hard drive's seek speed is significantly faster than the floppy and CDROM drives.

Hard drive head and head arm and servo positioning system is a general. The servo positioning system consists of a coil behind the head arm and an electromagnetic control system fixed on the base plate.

Because of the limitation of the positioning System, the head arm can only move between the internal and external tracks of the disc.

As a result, the head is always on the platter, regardless of whether it is turned on or off, and the difference is that the head stays in the start-stop area of the disc when it is switched on, and the head "flies" over the disk.

How is the data on the hard drive organized and managed? The hard disk is first logically divided into tracks, cylinders, and sectors, and its structure is seen in relation to 1-6.

Figure 1-6 Head, cylinder, and sector

Each surface of each platter has a read-write head, and the partition of the disk surface area is 1-7 seen. The surface of the head close to the spindle, that is, the smallest line speed, is a special area that does not store any data, called a start-stop or landing area (Landing zone). The data area is outside the start-stop area. In the outer ring, the farthest from the spindle is the "0" track. The storage of hard disk data is started from the outer ring.

So, how does the head find the position of the "0" track? Can be seen from figure 1-5. There is a "0" track detector, which comes after the initial positioning of the hard disk.

The "0" track is so important. It is a pity that so many hard drives are scrapped only because of the "0" track damage. The repair techniques for such faults are described in detail in the following chapters.

Figure 1-7 Start-stop and data area of the hard disk disc

Early hard drives need to execute a program called parking before each shutdown, and the effect is to get the head back to the start-stop area. Modern hard drives have been designed to abandon this small, albeit uncomplicated, but unpleasant flaw. When the hard disk is not working. The head stays in the start-stop area when it needs to read and write data from the hard disk. The disk starts spinning. When the rotational speed reaches the rated fast. The head is lifted by the airflow generated by the disc rotation, and the head is moved to the area where the disc is stored. The spinning of the disc is quite strong enough to hold the head up and keep a small distance from the disc. The smaller the distance. The higher the sensitivity of the magnetic head to read and write data, the higher the requirement of the hard disk parts. Early-design disk drives keep the heads flying a few microns above the disk surface.

Some designs later reduced the flying height of the head on the disc to about 0.1μm~0.5μm, and today the level has reached 0.005μm~0.01μm. This is only one of the thousand points of the human hair diameter.

The airflow allows the head to disengage from the opening surface. It also keeps it close enough to the surface of the disk, and is very closely followed by a rolling motion of the disks. The head flight is in a strictly controlled state. The head must be flown above the disk surface. Instead of touching the disc face, this position avoids scratching the magnetic coating. It is more important not to let the magnetic coating damage the head. However, the head can not be too far away from the disk surface, otherwise, can not make the disk surface to achieve a strong enough magnetization. Hard-to-read magnetization flip on shavings (the form of magnetic pole conversion is the way the data is actually recorded on the disk).

The hard drive head has a low flying height and fast speed, and once there is little dust entering the hard drive seal chamber. Or, once the head and the disc collide, it can result in data loss. The formation of a bad block, and even caused damage to the head and disk body. Therefore, the hard disk system seal must be reliable, in non-professional conditions can not open the hard disk sealing chamber, otherwise, the dust will accelerate the damage of the hard disk. In addition, the hard drive head of the seeker servo motor with a voice-coil rotary or linear motion stepper motor, in the servo tracking adjustment to accurately track the disc's track, so. Do not have impact collision when working hard, handle with care when moving.

Such a hard drive is a hard drive made with Winchest (Winchester) technology. So it is also called Wen Pan. Its structural characteristics such as the following.

① heads, platters and motion mechanisms are sealed in the disc body.

The ② head is in contact with the disc when it starts and stops, and rotates quickly due to the disc at work. Drive the magnetic head "suspension" on the disc to the flight state (aerodynamic principle). The height of "suspension" is about 0.1μm~0.3μm, this height is very small, figure 1-8 marked this height with hair, soot and finger print size, from here can intuitively "see" the height of how "high".

Figure 1-8 Disc structure and head height

The ③ head is not in direct contact with the disc when working. The magnetic head is small in size, the head can be made very delicate, the ability to detect the track is very strong, can greatly improve the bit density.

④ disk surface is very smooth, can do mirror use.

The following is a description of the meanings of "disc", "track", "Cylinder" and "sector".

1. Panel number

Hard disk disks are generally made of aluminum alloy substrate, fast hard disk may also be made of glass substrate.

The glass substrate is more easy to achieve the desired flatness and finish. and has a very high hardness.

The head drive device is a component that makes the head component move radially. There are usually two types of actuators. One is the drive device of the stepper motor of rack drive; There is also a voice coil motor drive.

The former is a fixed-projected transmission positioner, while the latter is returned to the correct position using servo feedback. The head drive has a very small equidistant distance to make the head part radially movable to change the track.

Each disc of the hard disk has two disk faces (Side), that is, the upper and lower disk surface, usually each disk surface will be used, can store data, become a valid disc, there are very few hard disk face number is singular.

Each of these effective discs has a plate number, sequentially numbered from top to bottom, starting with "0". In the hard drive system. The disk face number is also called magnetic number one, because each effective disk surface has a corresponding read and write head. Hard disk disc group in 2~14 tablets, usually have two or three platters, so the panel number (magnetic number one) for 0~3 or 0~5.

2. Track

The disk is divided into concentric circles when it is formatted. These concentric circles are called tracks. Tracks are numbered sequentially from 0 in the outward order. Each disk face of the hard drive has a 300~1 024 tracks. The number of tracks on each side of the new high-capacity hard drive is many others. The information is recorded in the form of a burst of pulses in which the concentric circles are not continuously recorded data, but are divided into segments of arcs that have the same angular velocity as the arcs. Because the radial length is not the same, the line speed is not the same, the outer ring line speed is greater than the line speed of the inner ring. That is, at the same speed, the outer ring is in the same period of time. The length of the circular arc is larger than the arc length across the inner ring.

Each arc is called a sector, the sector is numbered from "1", and the data in each sector is read or written as a unit at the same time. A standard 3.5in hard disk face typically has hundreds of to thousands of tracks. The track is "see" Missing, is only a special form of the plate magnetization of the magnetic area, in the disk format has been planned to complete.

3. Cylinder surface

The same track on all disks forms a cylinder. Usually called cylinder (Cylinder). The heads on each cylinder are numbered from the top down, starting with "0". The reading/writing of the data is performed on the cylinder, i.e. the head reads/writes the data first from the "0" head within the same cylinder. In turn down on the same cylinder on the different disk surface is the head on the operation, only in the same cylinder all the head of the whole read/write completed after the head is transferred to the next cylinder, because the selected head only by electronic switching can be, and select the cylinder must be mechanically switched. Electronic switching is fairly fast. It is much faster than the mechanical head moving towards the adjacent track, so the reading/writing of the data is performed on the cylinder. Instead of on the side of the disc. Other words. Once a track is filled with data, it is written on the next face of the same cylinder, and a cylinder is full before moving to the next sector to start writing data. Reading data is also done in such a way that it improves the read/write efficiency of the hard drive.

The number of cylinders (or the number of tracks per disk) of a hard drive depends on the width of each track (the same. is also related to the size of the head, depending on the size of the distance between the tracks determined by the positioning mechanism. For more in-depth content, please refer to other books, confined to space. No more in-depth introduction here.

4. Sectors

The operating system stores information on the hard disk as a sector (Sector), with 512 bytes of data and some other information in each sector.

A sector has two main parts: The identifier that stores the data location and the data segment where the data is stored. 1-9 of what you see.

Figure 1-9 The composition of the hard disk sector

An identifier is a sector header that contains three numbers that comprise the three-dimensional address of a sector: the head (or disk) where the sector is located, the track (or cylinder number), and the position of the sector on the track, the sector area code. A field is also included in the header. The display sector can reliably store data. Or if a fault has been found that is not suitable for use in the tag. Some hard disk controllers also record an indicator word in the sector header. Directs the disk to the replacement sector or track when there is an error in the original sector. At last. The sector header is terminated with a cyclic redundancy check (CRC) value for the controller to verify the readout of the sector header, ensuring accuracy.

The second major part of the sector is the data segment that stores the data, which can be divided into data and data-protection error-Correcting codes (ECC). During initial preparation, the computer fills this section with 512 virtual information bytes (the place where the actual data is stored) and ECC numbers corresponding to these virtual information bytes.

The sector header includes a sector area code that identifies the sector on the track.

Interestingly, these sector codes are not physically numbered consecutively. They do not have to be specified in any particular order. The design of sector headers agrees that the sector area code can be from 1 to a maximum value. In some cases up to 255. The disk controller does not care what number in the above range is arranged in which sector header. In very special cases, the sector can share the same number. The disk controller even simply reads out the data it finds, regardless of the size of the data area, or writes the data it needs to write.

The simplest way to number a sector is to l,2,3,4,5,6 sequential numbers.

Suppose the sectors are numbered sequentially around the track. So. During the process of processing data from a sector, the disk rotates too far, exceeding the interval of the sector (the interval is very small), and the next sector that the controller reads or writes to has passed through the head, which may be a considerable distance.

In this case, the disk controller can only wait for the disk to spin again for almost a week, enabling the required sectors to reach the head below.

Obviously, to solve the problem, by increasing the interval of fan interval is unrealistic, it will waste a lot of disk space. Many years ago, an outstanding project Engineer from IBM came up with a fantastic way to use a cross-factor (Interleave) to number a sector without sequential numbering.

The crossover factor is represented by a ratio method, such as 3:1, which indicates that the 1th sector on the track is sector 1th. Skipping two sectors i.e. the 4th sector is sector 2nd, the process continues until a logical number is assigned to each physical sector.

Like what. A disk with 17 sectors per track is numbered as a cross factor of 2:1: l,10. 2,11,3,12,4,13,5,14,6,15. 7. 16,8,17. 9. The cross-factor number by 3:1 is: l,7,13,2,8,14,3. 9,15,4,10. 16. 5,11,17. 6,12. When setting the cross-factor of the 1:l, it is assumed that the hard disk controller processes the information fast enough. All sectors on the track will only need to be rotated for a week, but assuming that the hard disk controller's post-processing action is not so fast, the number of laps on the disk equals the number of sectors on a track, and the ability to read all the data on each track. When the crossover factor is set to 2:1, the head reads all the data on the track, and the disk only needs to be transferred for two weeks. Suppose the cross factor of the 2:1 is still not slow enough, the number of weeks the disk rotates is approximately the number of sectors of the track. You can adjust the crossover factor to 3:1. 1-10 of what you see.

Fig. 1-10 example of effect demonstration of different cross factors

The typical MFM (Modified Frequency modulation) is seen in Figure 1-10. Improved FM coding) hard disk with 17 sectors per track, with three different sector cross-factor numbers drawn.

The sectors on the most outer ring track (cylinder NO. 0) are numbered consecutively in simple order, equivalent to the sector crossover factor is 1:1. The sector of track 1th (cylinder) is numbered by the cross factor of 2:1, while track 2nd is numbered by the sector cross factor of 3:1.

In the early days of hard disk Management, setting the crossover factor required the user to complete their own work. When you use a low-level formatter in the BIOS to format a hard disk, you need to specify a crossover factor. Sometimes it is necessary to set several different values to compare their performance, and then determine a better value, in order to achieve better performance of the hard disk. Today's hard drive BIOS has solved the problem on its own, so the general low-level formatter no longer provides this option setting.

When the system stores files on disk. In the manner of cylinder, head, sector, that is, the first head of the 1th track (that is, the first track of the 1th disc) of all sectors, and then, the same cylinder is the next head, .... Once a cylinder is fully stored, it advances to the next cylinder until all the file contents are written to disk. The system also reads the data in the same order. read out the data by telling the disk controller to read out the cylinder number, the number of magnets, and the sector area code (three components of the physical address) of the sector. The disk controller directly moves the head assembly to the corresponding cylinder and the corresponding head is selected. Wait for the requested sector to move to the head. When the sector arrives. The disk controller reads the header of each sector, comparing the address information in these headers with the expected detected head and cylinder number (that is, seek), and then, looking for the required sector code. When the disk controller finds the sector header, it determines whether to convert the write circuit or read the data and tail records, depending on whether the task is a write sector or a read sector.

When a sector is found, the disk controller must post-process information for that sector before continuing to look for the next sector.

Assuming that the data is read, the controller calculates the ECC code for this data, and then. Compare the ECC code with the recorded ECC code. Assuming that the data is written, the controller calculates the ECC code for this data, which is stored with the data.

During the necessary processing of the data in this sector by the controller. The disk continues to rotate.

Because the post-processing of information takes a certain amount of time. During this time, the disk has been turned to a considerable angle.

The determination of cross-factor is a system-level problem. The crossover factor for a particular hard drive depends on the speed of the disk controller, the clock speed of the motherboard, the operating speed of the output bus connected to the controller, and so on. Assuming that the cross-factor value of the disk is too high, it takes more time to wait for the data to be deposited and read out on disk. Assuming that the cross-factor values are too low, disk performance is greatly reduced.

Already mentioned earlier. When the system writes information to the disk, it fills a track and then goes to the next head of the same cylinder. When the cylinder is full. Then turn to the next cylinder face. From one track on the same cylinder to another track, move from one cylinder to the next. Each transition requires time, during which the disk remains rotated. This poses a problem: Assume that the system has just finished writing the previous sector of a track, and that the best cross factor ratio has been set. You are now ready to write to the first sector of the next track. Then. Must wait until the head is converted. Let the head assembly be ready again to be positioned on the next. Assuming such an operation takes longer than a point, although it is interleaved, the head will still arrive late. The solution to this problem is to take the original track location as the benchmark, the new track on all the sector area to move about one or several sector location, this is the head twist oblique. The head twist can be understood as the cross-factor between the cylinder and the cylinder, which has been set up by the production plant, and the user generally does not have to change it. The change in the head skew is more difficult, but they only work when the file is very long and exceeds the end of the track to read and write, so. The skew setting does not result in a much less time-lost than the loss of an incorrect sector cross-factor value.

Cross-factor and head skew can be tested and changed using special tool software. More detailed content is no longer detailed here, after all, many users today have not seen these parameters.

The sector area code is stored in the sector header, and the information about the sector crossover factor and the head skew is also stored here. Initially, the hard drive low-level formatter simply exercised the specialized function of the disk controller to complete the setup task.

Because this process can destroy all the data on low-level formatted tracks, it is rarely used.

The sector crossover factor is set by the number written to the header of the sector, so each track can have its own cross-factor.

On most drives. All tracks have the same crossover factor. But sometimes due to operational reasons. It may also lead to different sectors of each track crossing factors. When factors such as cross-reset program works, due to power interruption or man-made, this can cause some changes in the orbit coefficient, and there are many cross--track factors unchanged.

Such contradictions are not adversely affected by the computer, but are only the factors that work best across the track speed than other tracks.

The hardware structure and working principle of internal hard disk are explained in detail.