Deep understanding of Hard Disk Structure

Not long ago, my old computer's hard drive broke down and there was a lot of information in it, so it was very depressing. I wanted to recover the hard disk data and asked about the price. I was shocked and decided to learn more about the hard disk restoration technology. You must have a full understanding of the overall physical structure of the hard disk before you have a deep understanding of disk opening data recovery. As an accessory with high precision, the external structure of the hard disk is relatively simple. The real high-tech content lies in the inside of the disk.

1. External Structure of the hard disk

The external structure of the hard disk is not complex. It consists of the Power interface, data interface, and control circuit board. The external structure of the IDE Hard Drive, Serial-ATA hard drive, and SCSI hard drive is slightly different.
Power supply Interface
The power interface is used to connect the power of the host to provide sufficient power for hard disk operation. Generally, hard disks use the most common 4-pin D-shape Power interface. However, you must note that the latest
The Serial-ATA hard drive is not replaced by a 4-pin D-Power interface, but by an easy-to-plug interface. This interface has 15 pins, but its width is equal to that of the previous power supply interface. Hard Drive Controller manufacturers such as Silicon, Promise, and other motherboard manufacturers provide essential power adapter lines in their product packaging. At this time, you can still use 4-pin D-type power interface. From the future development trend, The ATX power supply that can directly expand the Serial-ATA Hard Drive Power Interface line will become more and more popular in the future.
Data Interface
The data interface is an important part of the hard disk. It is used to connect the nanqiao chip on the motherboard or other independent disk controller chips. Taking the most common IDE hard drive as an example, there is a 40-pin interface in front of it. You need to connect the motherboard or the IDE interface on the raid/ATA card through a flat ide data cable. In the past, older hard disks used common 40pin data lines. However, to improve the transmission performance of hard disks, major hard disk manufacturers have jointly launched the ultra DMA transmission mode, that is, the ata66/100/133 hard disk transmission mode. Because the amount of data transmitted in this mode increases, it is necessary to ensure the accuracy of signal transmission. To improve the electrical performance of the IDE data line, we used to increase the number of 40pin ide data lines to 80pin, where 40pin is used for signal transmission, and 40pin is used for ground line, used to effectively shield clutter signals.
Compared with IDE hard disks, SCSI hard disk interfaces are more complex. The SCSI hard disk interface types can be roughly divided into 68-pin interface and 80-pin interface, the former can be directly connected using the SCSI control card, and the 80-pin interface product must use the LVD adapter. It should be noted that the quality of the LVD adapter and the SCSI data line determines the performance of the SCSI hard disk, and the poor quality of the adapter will degrade the performance. in addition, when installing a SCSI hard disk, you do not need to design a master-slave concept similar to an IDE hard disk. Instead, you need to use the ID number to differentiate it.
Among all hard disks, the data cable connection of serial-Ata is the simplest, because it adopts the point-to-point connection mode, that is, each serial-Ata cable (or channel) only one hard disk can be connected. You do not need to set a Master/Slave jumper like the IDE hard disk. It is commendable that the serial-Ata data line occupies a small amount of space, which is very conducive to heat dissipation and can improve the stability of data transmission.
Control Circuit Board
The control circuit board is usually exposed to the bottom surface of the hard disk to facilitate heat dissipation. However, some brands of hard disks have completely closed it, which can better protect various control chips and reduce noise. The control circuit board of the hard disk consists of the spindle speed control circuit, head drive and servo positioning circuit, read/write control circuit, control and interface circuit. In addition, an efficient single-chip ROM chip is used to solidify the software. It is used to initialize the hard disk, execute power-on and start the spindle motor, and add the initial tracing, locating, and fault detection. Of course, high-speed cache is also indispensable for the control board, generally with 2 ~ 8 Mb SDRAM.

The read/write control circuit is the most important in the hard disk control circuit board. It has two main functions: first, it is responsible for converting binary codes into analog signals. When data information needs to be written, the binary code representing the data is transmitted by the central processing system to the head. This circuit is the only way to pass these binary codes, it is responsible for converting the binary code here into a simulated signal that can change the current size and transmitting it to the head. It is also responsible for converting the analog signal into a binary code and amplifying the signal. When reading data, the head obtains the current generated by the magnetic field from the disk. When the current is transmitted to the center processing system, it must also go through the front amplification circuit, at this time, the circuit works to convert the current of the analog signal to the binary code that can be recognized by the Central Processing System, and to enlarge the weak signal.

For most serial-ATA hard disks, we can also see a transfer chip. The 7200.7 series is not a real serial-ATA hard drive during development, but is implemented through the transfer chip of Marvell. The function of this chip on the hard disk is to convert the source and source parallel signals generated by the hard disk into serial signals and transmit them to the Southern bridge chip of the system, or convert the received serial signal to the parallel signal that the hard disk can receive. In this way, the conversion process will inevitably lead to performance loss. Of course, it does not mean that the serial-ATA Hard Disk using the transfer chip is not good, but that it is difficult to exert the maximum power of the serial-ATA hard disk, we also hope that such chips will disappear from the serial-ATA hard disk in the future.

 

2. Internal Structure of the hard disk

 

Although there are some differences between various hard disks in terms of the external structure, the internal structure is still completely the same. After all, the basic working mode of the hard disk will not change. After opening the hard disk shell, we can see the mysterious internal world. Its core parts include the disk body, spindle motor, read/write head, track motor, and other main components. However, we need to remind everyone that we should never open the shell of the hard disk at will, which will make the entire hard disk decommission 100%, because the internal disk of the hard disk cannot be contaminated with a drop of dust, otherwise it will be immediately decommissioned. Generally, maintenance of the internal structure of the hard disk even requires strict cleaning room.
From the physical point of view, the disk is divided into four structures: the disk side, the track, the cylinder, and the sector. The magnetic surface is the upper and lower sides of each disk. The first side of the first disk is 0, and the next side is 1. The first side of the second disk is 2, and so on ....... A magnetic track is a number of concentric circles divided into disks during disk formatting. The magnetic channels on the outermost layer are 0 and increase toward the magnetic surface center. The data in the closest part to the center is not recorded, which is called the landing zone. It is the position where the head starts and stops each time the hard disk is started or shut down. The magnetic channels with the same radius on all disks constitute a cylinder, which is called a cylinder. A cylindrical disk can be used to calculate the capacity of a logical disk.

Slice is the most basic unit for disk data access, that is, dividing each track into an area adjacent to two radius. This makes it difficult to understand that each track contains an equal number of sectors, the start of the slice contains the unique ID of the slice address. The Slice and slice are separated by gaps to facilitate identification by the operating system. In fact, the structure of the disk is very similar to that of a floppy disk. However, the disc is composed of multiple overlapping disc segments separated by washers, And the disc is made of metal disc (IBM used glass as the material), the surface is extremely smooth, and coated with magnetic substances.
Read/write head assembly

The read/write head component consists of a read/write head, a drive arm, and a drive shaft. During actual operation, the head scans the disc with a fixed radius through the drive arm and drive shaft to read and write data. The head is a combination of multiple heads made by the integrated process and adopts a non-contact structure. After the hard disk is powered on, the read/write head is flying on the high-speed rotating disk surface, and the gap between the flying height is only 0.1 ~ 0.3 μm for extremely high data transmission rate. The new MR (Magnetoresistive heads) Magnetic Head adopts a read/write splitting head structure. The traditional magnetic induction head is used for write operations, while the MR head is used for read operations.
Since IBM invented the Winchester hard drive in 1973, the basic principles of the core mechanical structure of the hard drive have not been removed from the "Winchester" Mode for nearly 30 years. The essence of the "Winchester" mode is that each storage surface of a disk with a fixed and high-speed rotation has a head that moves radial along the disk. Objectively speaking, this mode severely hinders Hard Drive Speed improvement, but it is not easy to change it. At least the current mainstream hard drive has not yet taken the first step. In the future, there may be multi-head hard disk technology. By coordinating multiple independent heads, the track time of the heads will almost completely offset each other, and the duration of reading and writing data blocks will partially offset. When one head reads and writes a segment, the other head searches for the next segment. After finding the segment, you can perform read and write operations immediately or enter the preparation status of the read and write operations, wait for the previous head to complete the previous section and take over the job immediately. It is optimistic that this technology will enter the substantive application phase five years later.
Head Drive Mechanism
For a hard disk, the head drive mechanism is like a commander, which controls the reading and writing of the head, directly sending commands for the drive arm and the drive shaft. The head drive mechanism consists of a sound ring motor, a head drive car, and a anti-vibration mechanism. The head Drive Mechanism correctly drives the head and precisely locates the track specified by the system command in a short time to ensure the reliability of data reading and writing.

Generally, the motor of the head mechanism includes three types: stepping motor, torque motor and audio ring motor. Currently, the hard drive is mostly driven by audio ring motor. The sound ring is the coil with a magnetic rod connected to the head in the middle. When the current passes through the coil, the magnetic rod will be displaced, and then drive the car carrying the head, the head movement distance is obtained based on the information encoding of the Controller's head position on the disk to achieve accurate positioning. It is worth noting that if the head drive mechanism is poorly designed, it may easily cause damage to the disk or bad track. The advanced head drive mechanism should effectively optimize the reading mode, provide performance, and make appropriate judgments and timely and appropriate measures against unknown situations such as sudden power outages and severe external shocks.

 

3. Spindle Components

The spindle components of the hard disk are mainly bearings and motors. We can generally think that the bearing determines the noise performance of a hard disk, while the motor determines the performance. Of course, this is not completely correct, but it basically expresses the importance of these two items in the hard disk. From ball bearings to oil-immersed bearings to liquid bearings, Hard Drive bearings are constantly being improved. At present, liquid bearings have become an absolute mainstream market, supported by segate, matrox, WD, IBM, sunbench, and many other vendors. Because the liquid is used as the bearing, there is no direct friction between metals. In this way, apart from extending the life of the spindle point solution and Reducing Fever, the most important point is to achieve a breakthrough in hard disk noise control. However, it should be pointed out that the use of liquid bearings does not have any benefits for the performance, but may even extend the seeking time. It seems that noise and performance are a contradiction that is always hard to balance.
As for the motor, Its intuitive understanding is the speed at which the head rotates. The higher the speed, the larger the area of the scanned disk, so the read/write speed can also be improved accordingly. At present, the speed of mainstream IDE hard disks and serial-ATA hard disks is 7200 RPM, while a few low-end IDE hard disks and notebook hard disks are only 5400 rpm and 4200 rpm. Relatively speaking, the speed of SCSI hard disks is much higher. 10000 RPM seems to be an entry-level product, and mainstream products are maintained at 15000 rpm.