Talking about the error statement about hard drives
[Abstract] From 1957 IBM, IBM has successfully developed the first true hard disk memory in the real sense of hard disk, and people have been misunderstood for hard drives. Many people think that the hard disk is vacuum, 16 heads in the hard disk. I analyzed from these two questions, making the reader out of the misunderstanding.
[Keyword] hard disk structure, hard disk works; hard disk addresses; logical address; physical address
Almost all computers are used to use hard drives, and hard drives are widely understood as an indispensable important part of the computer. In short ten years, from dozens of M developed to now a few hundred g, the capacity of more than 10,000 times. At the same time, the hard drive has a natural vulnerability, so that everyone will soon be respectful, because even if a little impact will cause fatal damage to it. Because of this, the hard disk has a mysterious veil. So far, many people include some computer professionals are thinking: "There is a vacuum in the hard disk," a hard disk has 16 heads. " Why do you have such misunderstandings? The reason is that there is no explanation of this problem in various textbooks. This article will begin to explain these two problems from the beginning of the physical structure of the hard disk.
I. Hard disk internal structure
After removing the hard drive, we can see that the hard disk consists of major components such as spindle, magnetic disk, magnetic head, magnetic head arm, motor.
Now the hard disk, whether it is IDE or SCSI, all of which are "Warcome" technology, all of which are characterized:
The disc is the surface of the disc at an aluminum alloy (new material also useful glass, such as IBM Tenglong Second Generation). These magnetic powders are divided into several concentric circles, which are called "tracks". The disc body consists of a plurality of discs, which are superimposed together in a sealed box, and they rotate at a very high speed under the drive of the spindle motor, and their rotation speed is 3600, 4500, 5400, 7200 or even even the above. The magnetic head is used to read or modify the state of magnetic substance on the disc, which generally, each magnetic surface will have a magnetic head, starting from the top, starting from 0. When the magnetic head is stopped, it is in contact with the disk, but is a flight state when working. The magnetic head is taken in a manner in which the tray is stored, the landing area does not store any data, and the magnetic head is started and stops in this area, and there is no problem with any data. When reading data, the disc is rotated at high speed, and since a delicate aerodynamic design is taken on the magnetic head motion, the magnetic head is in the "flight state" of 0.2 - 0.5 microns height from the disk surface data area. It is neither a wear with a disk, and it is well possible to read data. The temperature of the magnetic head can float, which is completely the buoyancy of the air. If there is no air, the magnetic head will be in direct contact with the disk unless it is possible to make the zero-grinding absolute plane, otherwise the entire disk surface and the head are worn in an instant.
The motor in the hard disk is a brushless motor, which is small under high-speed bearing support, and it can work for a long time.
High-speed rotating tray produces a significant gyro effect, so the hard drive in the work should not move, otherwise the workload of the bearing will be increased. The search feed motor of the hard disk magnetic head is multi-voiced rotation or a straight motion step motor, and the track is accurately tracked under the adjustment of the feed track.
two. Precautions for hard drives:
1. The hard disk cannot be suddenly turned off when the hard disk is working. When the hard disk is started, it is generally in high-speed rotation. If we suddenly turn off the power in the middle, it may cause the magnetic head to violently frozen the hard disk. Therefore, it is best not to shut down. When shutting down, it is necessary to pay attention to whether the hard disk indicator on the panel is still flashing. Only when the hard disk indicator stops flashing, the hard disk ends the read and write, turn off the computer's power switch. Suddenly, the power outage will make the magnetic head in direct contact with the disc in contact with the disc, which may cause a bad sector on the surface of the disk. 2. It is very huge to prevent dust from dust to the hard drive. This is because the hard disk is easily attracted to dust particles in the dust, and the attracted dust is long-term accumulated in the internal circuit of the hard disk, and the components will affect the heat of the electronic components, so that the board isometric The temperature of the device rises, generates leakage and burn the component. Even so, but don't worry that dust will enter the hard disk, the disk is completely sealed, the only way to communicate with the interior is the servo port. Readers who are familiar with the hard drive know that there is a hole on the side of the hard disk, which is generally sealed with aluminum stickers, and some even use metal sheets to enclose the stickers of the sea, prevent it from being destroyed, this is the servo. Some salesperson misunderstand the internal part of the hard disk, and this sealing is called this "vacuum seal", which is wrong. When the seal is damaged, the dust will enter the tray, first of all, the hard disk is very slow, followed by the hard disk's noise. In this case, the length of use will result in the loss of the hard disk data, which may cause damage to the disc. So we have to pay special attention not to destroy the seal.
Different dust may also absorb moisture, corrode the electronic line inside the hard disk, causing some inexplicable problems. Therefore, the dust is small, but the harm to the hard disk is unhaffably. Therefore, environmental hygiene must be maintained, reducing the humidity and dust in the air.
3. To prevent temperature over high temperature, it also affects the life of the hard disk. A certain amount of heat is generated when the hard disk is working, and there is a heat dissipation problem in use. The temperature is preferably 20 ~ 25 ° C, the temperature is too high or too low, can cause the hard disk circuit component failure, and the magnetic media will also cause recording errors due to thermal translation; the temperature is too low, the water in the air is condensed in the integrated circuit component On, it may cause a short circuit. Also, try not to bring your hard drive near strong magnetic field, such as speakers, speakers, motors, radios, mobile phones, etc., so that the data recorded by the hard disk is damaged due to magnetization. Don't have a hit collision when working in the hard disk, and be careful when moving.
Third. The number of physical heads and logical heads of the hard disk
Prior to explaining the physical head and logic head, list this set of data first:
Cylinders Heads Sectors
2491 255 63
Hard disk capacity = 2491x255x63x512 = 19.08g
The above parameters are obtained from a gold diamond 20g hard drive. It is obvious that its column number is 2491, the number of magnetic head is
255, the number of sectors on each track is 63. The misunderstanding begins, if we don't know the physical structure of the hard disk, we will think that this hard disk has 255 heads. But try it carefully, it will find it not to be established.
A single-sided disk requires one
Tag, double-sided disc needs
Two magnetic heads, if all are double
Vessel plate, 255 heads at least
128 discs, and 128
The thickness of the disc is stacked than a hard
More than a thick, this has not been considered
The gap between the discs.
In fact, we look in the BIOS.
The parameters of the reached hard drive are just a logical value. Most of the hard drives are single-disc, single heads. Take the gold diamond nine generation 80g, it is a single disc. That is to say, it has only one head, but why do we display 255 heads when testing the test software? The answer has to be said many years ago. Since the earlier hard disk capacity is relatively small, when the design of the BIOS is designed to convert the address from the address register of the INT 13 to the address register, only 10-bit cylindrical addresses in INT 13 management are used to correspond to the hard disk. The 16-bit cylindrical register, and only 6 bits of sector addresses correspond to the 8-bit sector register in the hard disk, where the bit is not set to 0. And only 4 bits will represent the head. Therefore, at this time, the maximum number of disk cylinders is 1024 (10 times), the maximum number of the magnetic head is 16 (4 times), the maximum number of sectors is 63 (2 of 6 times) . Therefore, the number of sectors that can be addressed will become 1,032,192 (1,024 x16x63). The capacity of a sector is 512 bytes, that is, if the CHS addressing mode, the maximum capacity of the IDE hard drive is 528.4MB. This way of addressing is Normal mode.
Using the LBA (Logical Block Addressing logic block addressing mode management hard disk space can reach 8.4GB. In LBA mode, parameters such as the set cylinders, heads, and sectors are not physical parameters of the actual hard disk. When accessing the hard disk, the logical address determined by the cylinder, the head, sector, etc. is converted to the physical address of the actual hard disk by the IDE controller. In LBA mode, the maximum number of magnetic heads can be set is 255, and the remaining parameters are the same as normal mode.
At this time, the number of heads is just a virtual number, and there is only one physical head. But hard disk manufacturers convert the physical address of the hard disk into a virtual logical address in order to allow the BIOS system to properly identify and use the hard disk. And in this address we saw 255 heads. The actual work is that the number of cylinders is in addition to one 255, while the number of magnetic head is multiplied by a 255, and the total representation is still not changed.
Four. Thoughts arising from two wrong statements
After half a century, the hard disk has been in the past, the speed has arrived in the past. However, its development has been restricted by old technologies, and has to sacrifice some good methods and technologies in order to compatibility. Now SATA's hard drive has a substitute PATA hard drive, and performance values chased SCSI hard drives. The hard disk is an indispensable part of the computer, and walks into thousands of households. Like the "Hard Disk is vacuum", the sealing of the hard disk servo is called "vacuum seal", "is widely circulated between major IT stores and professionals in the country. Today, we have to popularize its basic knowledge today.
[references]
[1] Zhang Zhongshi. Large-capacity hard disk repair technology and data management. University of Electronic Science and Technology Press
[2] Lin Junhao Liu Dan and other modifications. DIY hard disk management / data backup / system recovery. People's Posts and Telecommunications Publishing House
