I chose to tile the mobile hard disk, but I came in to discuss it in detail. Why?

Hard disk is the main storage medium of computer, which consists of one or more disks made of aluminum or glass. These disks are covered with ferromagnetic materials. Most hard disks are fixed hard disks, which are permanently sealed and fixed in hard disk drives. However, nowadays, mobile hard disks are becoming more and more popular and there are more and more types.

The hard disks used by most desktop computers use either IDE interface or SCSI interface. The advantage of SCSI interface hard disk is that up to seven different devices can be connected to the same controller panel. Because the hard disk rotates at a constant high speed of 3000- 10000 revolutions per second, it only takes a short time to read data from the hard disk. In a notebook computer, the hard disk can stop spinning when idle, thus extending the battery life. The storage capacity of the old hard disk is only 5MB, and the disk with a diameter of 12 inch is used. Now the storage capacity of hard disk is as high as tens of GB. The disk diameter used in desktop computer hard disk is generally 3.5 inches, and the disk diameter used in notebook computer hard disk is generally 2.5 inches. The new hard disk is generally formatted at the assembly plant in order to store some original sector identification information on the hard disk.

Sata (Serial ata), namely serial ata interface, is a new hard disk interface technology first proposed by intel Corporation in early 2000. Although compared with traditional parallel ata storage devices, sata hard disk has incomparable advantages. The real serialization of the disk system started from the motherboard, and the sata interface of the motherboard was ready long before the serial hard disk was officially listed. However, before intel ich5, sis964 and via vt8237 which really supported sata, the sata interface of the motherboard was realized by a third-party chip. These chips are mainly sil 3 1 12 of siliconimage and pdc20375 and pdc20376 of promise, which are based on pci bus, and some products are also made into special pci raid control cards.

Hard disk maintenance

As one of the most durable devices in computer accessories, hard disk can be used for 6 ~ 7 years if it is well maintained. The following describes how to properly maintain the hard disk.

Hard disk maintenance is divided into two aspects. First, from the perspective of hardware, especially DIY players of supercomputers, we should pay attention to the following problems. They usually don't need a chassis. Putting the computer on the desktop is beneficial to heat dissipation and easy to disassemble, which greatly increases the chance of damaging the hardware, especially the hard disk, because when they start working, they are generally in a state of high-speed rotation and are not fixed on the desktop. Instability is the most likely cause of violent friction between the head and the disk, which will damage the hard disk. There is also the need to prevent the computer from getting too hot when it is used. Excessive temperature will not only affect the normal operation of the hard disk, but also cause damage to the hard disk.

Excessive temperature will affect the data reading sensitivity of thin film magnetic head, change the clock frequency of crystal oscillator, cause the failure of hard disk circuit components, and cause recording errors of magnetic media due to thermal expansion effect.

Too high a temperature is not appropriate, and too low a temperature will also affect the work of the hard disk. Therefore, in the air-conditioned room, be careful not to drop the temperature of the air conditioner too much, which will generate steam and damage the hard disk. Generally, it is advisable to keep the room temperature at 20 ~ 25℃. Next, talk about the problem of hard disk in use.

Many friends don't form a good habit when using computers. When they are finished with their computers, they will unplug them before they are completely shut down. Some people turn off the switch directly after using the computer, and the hard disk has not been reset yet. So when you turn it off, be sure to pay attention to whether the hard disk indicator on the panel is still flashing. Only when the hard disk indicator light stops flashing and the hard disk finishes reading and writing can we turn off the power switch of the computer, thus forming a good habit of using the computer.

Some friends pay great attention to the maintenance of the hard disk, but due to improper operation, it will also cause some damage to the hard disk.

Someone read in the newspaper that the data on the hard disk should be sorted regularly, but he didn't realize the word "regularly". He sorted the hard disk after using the computer every day, thinking that it would improve the speed, but he didn't know that it would improve the utilization rate of the hard disk. Over time, the hard disk not only failed to achieve the effect, but turned it upside down.

Of course, if you don't tidy up your hard disk for a long time, it won't work. If a lot of fragments are accumulated, it may take us a long time to read a file in the future, which will not only reduce the access efficiency, but also damage the track. The problems we often encounter are not limited to these.

Also, when some friends copy files, they always copy several files at a time. In exchange, they get screams from the hard disk. Antivirus the hard disk regularly. For example, CIH will destroy the partition table of the hard disk, resulting in the loss of your precious "wealth". Do not use the hard disk compression technology in system tools. Now that the hard disk is very large, there is no need to save space on that hard disk. What's more, this will greatly slow down the speed of reading and writing data on the hard disk, and at the same time, it will unconsciously affect the life of the hard disk.

It can be seen that it is very important to form a good habit of using computers, which will directly affect the life of computers and even hard disks. Get into the habit slowly, so that your computer can work for you for a long time.

Physical structure

1, head

Magnetic head is the most expensive component in hard disk, and it is also the most important and key link in hard disk technology. The traditional magnetic head is an electromagnetic induction head which combines reading and writing. However, reading and writing on the hard disk are two completely different operations. Therefore, the design of this two-in-one magnetic head must consider both reading and writing characteristics, which leads to the limitations of hard disk design. The magnetoresistive head (MR head) adopts the separated head structure: the writing head still adopts the traditional magnetic induction head (MR head can't write), and the reading head adopts the new MR head, which is called inductive writing and magnetoresistive reading. In this way, the design can be optimized according to their different characteristics to obtain the best read/write performance. In addition, MR magnetic head senses the signal amplitude through the change of resistance instead of current, so it is quite sensitive to the signal change, and the accuracy of reading data is also improved accordingly. Moreover, because the reading signal amplitude has nothing to do with the track width, the track can be made very narrow, thus improving the disk density, reaching 200MB/ in2, which can only reach 20MB/ in2 by using the traditional magnetic head, which is the main reason why the MR magnetic head is widely used. At present, MR heads have been widely used, and giant magnetoresistance heads made of multi-layer structure and materials with better magnetoresistance effect are gradually popularized.

2. Track

When the disk rotates, if the heads stay in one position, each head will draw a circular track on the surface of the disk. These circular tracks are called tracks. These tracks are invisible to the naked eye, because they are only areas magnetized in a special way on the surface of the disk, and the information on the disk is stored along such tracks. Adjacent tracks are not adjacent, because the magnetization units are too close, the magnetism will affect each other, which also brings difficulties to the head reading and writing. A 3.5-inch floppy disk with 1.44MB has 80 tracks on one side, but the track density on the hard disk is much higher than this value, usually there are thousands of tracks on one side.

3. Department

Each track on the disk is equally divided into several arc segments, which are the sectors of the disk. Each sector can store 5 12 bytes of information. Disk drives should read and write data to the disk in sectors. 1.44MB3.5-inch floppy disk, each track is divided into 18 sectors.

4. Cylindrical surface

A hard disk usually consists of a set of overlapping disks. Each disk surface is divided into an equal number of tracks, and numbered from "0" on the outer edge. Tracks with the same number form a cylinder, which is called the cylinder of the disk. The number of cylinders on the disk is equal to the number of tracks on the disk surface. Because each disk has its own head, the number of disks is equal to the total number of heads. The so-called CHS of the hard disk, namely Cylinder, Head and Sector, can determine the capacity of the hard disk as long as the CHS number of the hard disk is known, and the capacity of the hard disk = number of cylinders, number of heads and number of sectors 5 12B.

Brief introduction of hard disk logical structure

1. hard disk parameter description

Today, the hard disk parameters that people often say are still the ancient CHS (cylinder/head/sector) parameters. So why use these parameters and what do they mean? What are their values?

A long time ago, when the capacity of the hard disk was still very small, people used a floppy disk-like structure to make the hard disk, that is, each track of the hard disk had the same number of sectors, which produced the so-called 3D parameters, that is, head, cylinder, sector and corresponding addressing methods.

These include:

The number of magnetic heads indicates how many magnetic heads there are in the hard disk, that is, how many disks there are, up to 255 (stored in 8 binary bits);

Cylindrical surface indicates that there are several tracks on each disk of the hard disk, and the maximum is 1023 (stored by 10 binary bit);

Sectors indicate how many sectors there are on each track, up to 63 (stored in 6 binary bits).

Each sector is generally 5 12 bytes, which is unnecessary in theory, but it seems to have no other value.

Therefore, the maximum disk capacity is:

255 *1023 * 63 * 512/1048576 = 8024gb (1m =1048576 bytes) or units commonly used by hard disk manufacturers:

255 *1023 * 63 * 512/100000 = 8414 GB (1m =1000000 bytes).

In CHS addressing mode, the values of head, cylinder and sector range from 0 to Heads- 1, 0 to Cylinders- 1, 1 to Sectors (note that it starts from 1).

2. Introduction of basic Int 13H call

BIOS Int 13H call is a basic disk I/O interrupt call provided by BIOS, which can complete functions such as reset, read, write, check, locate, diagnose and format. Disks (including hard disks and floppy disks). It uses CHS addressing mode, so it can access about 8 GB hard disk at most (unless otherwise specified in this article, it is 1m = 1000).

3. Brief introduction of modern hard disk structure

In the old hard disk, because the number of sectors of each track is equal, the recording density of the outer track is much lower than that of the inner track, thus wasting a lot of disk space (just like a floppy disk). In order to solve this problem and further improve the capacity of hard disk, people use equal density structure to produce hard disk. In other words, the outer track has more sectors than the inner track. After adopting this structure, the hard disk no longer has actual 3D parameters, and the addressing mode is changed to linear addressing, that is, addressing by sectors.

In order to be compatible with old software using 3D addressing (such as software using BIOSInt 13H interface), an address translator is installed in the hard disk controller, which is responsible for translating old 3D parameters into new linear parameters. This is why there are many options for 3D parameters of hard disks (different working modes correspond to different 3D parameters, such as LBA, large and normal).

4. Introduction of extended Int 13H

Although modern hard disks have adopted linear addressing, due to the basic Int 13H limitation, programs using BIOS Int 13H interface, such as DOS, can only access the hard disk space within 8 G. In order to break this limitation, several companies, such as Microsoft, have formulated the extended Int 13H standard and used linear addressing to access hard disks, thus breaking through the 8 G limitation and increasing the access to hard disks.

Basic parameter

I. Capacity

As the data storage of computer system, the capacity of hard disk is the most important parameter.

The capacity of the hard disk is in megabytes (MB) or gigabytes (GB), 65438+GB = 1024 MB. However, hard disk manufacturers usually take 1G= 1000MB as the nominal capacity of the hard disk, so the capacity we see in BIOS or when formatting the hard disk will be smaller than the nominal value of the factory trademark.

For users, the capacity of hard disk is just like memory, and it will never be too little or too much. Windows operating system brings us not only simpler operations, but also larger and larger file sizes and quantities. Some applications will eat up hundreds of megabytes of hard disk space easily, and there is a growing trend. Therefore, it is wise to prepare in advance when buying a hard disk. At present, the capacities of mainstream hard disks are 10G and 15G, and the large-capacity hard disks above 20G have gradually become popular.

In fact, the larger the hard disk capacity, the cheaper the price per byte. For example, the price of fireball 10G is 1000 yuan, and the price per g byte is 100 yuan; The price of fireball 15G is 1 160, which is less than that of 80 yuan per GB.

The capacity index of hard disk also includes the storage capacity per disk of hard disk. The storage capacity per disk refers to the capacity of a single hard disk. The larger the storage capacity of each disk, the lower the unit cost and the shorter the average access time. At present, the single disk storage of most hard disks on the market is above 6.4G, and the higher one is 10G.

Second, speed.

Speed (or spindle speed) refers to the revolutions per minute of the hard disk, and the unit is rpm.

At present, the speed of mainstream IDE hard disks on the market is generally 5200 rpm or 5400 rpm, while Seagate's Grizzly Bear series and Maxtor reach 7200 rpm, which is the fastest among IDE hard disks. As for the hard disk with SCSI interface, the speed generally reaches 7200 rpm, and even higher reaches 10000 rpm.

Third, the average visit time.

The average access time refers to the time required for the head to reach the target track position from the starting position and find the data sector to be read and written from the target track.

The average access time reflects the reading and writing speed of the hard disk, including the seek time and waiting time of the hard disk, namely:

Average access time = average seek time+average waiting time.

Hard disk average seek time refers to the time required for the hard disk head to move to the designated track on the disk surface. Of course, the shorter the time, the better At present, the average seek time of hard disk is usually between 8ms and 12ms, while SCSI hard disk should be less than or equal to 8ms.

The waiting time of hard disk, also called waiting time, refers to the time when the head is already on the track to be accessed, waiting for the sector to be accessed to rotate below the head. The average waiting time is half of the time required for a disk to rotate once, and usually it should be less than 4 milliseconds.

Fourth, the transmission rate

Data transfer rate The data transfer rate of a hard disk refers to the speed at which the hard disk reads and writes data, in megabytes per second (MB/s). Hard disk data transfer rate includes internal data transfer rate and external data transfer rate.

The internal transfer rate, also known as the persistent transfer rate, reflects the performance of the hard disk buffer when it is not used. The internal transmission rate mainly depends on the rotational speed of the hard disk.

External transfer rate, also known as burst data transfer rate or interface transfer rate, nominally refers to the data transfer rate between the system bus and the hard disk buffer. The external data transfer rate is related to the type of hard disk interface and the size of hard disk buffer.

At present, the maximum external transmission rate of fast ATA interface hard disk is 16.6MB/s, while that of Ultra ATA interface hard disk is 33.3 MB/s. ..

Verb (abbreviation for verb) concealment

Like the RAM cache on the motherboard, the purpose of hard disk cache is to solve the problem of mismatch between the reading and writing speeds in the front and back of the system, so as to improve the reading and writing speed of the hard disk. At present, the cache of most IDE hard disks is between 128K and 256K, while Seagate Grizzly series uses 5 12K cache.

Hard disk data protection technology

The capacity of hard disk is getting bigger and bigger, and more and more data are stored. So, how safe is it to store so much data in such an iron box? Although the MTBF of most hard disks has reached more than 300,000 hours, it is still not enough, and a failure is enough to cause disastrous consequences. Because for many users, especially business users, data is the most expensive part of PC system, what they need is to be able to predict faults in advance. It is this demand and trust crisis that drives manufacturers to seek hard disk security monitoring mechanism, so a series of hard disk data protection technologies came into being.

1, Royal Swedish Technology Company

The full name of S.M.A.R.T technology is self-monitoring, analysis and reporting technology, namely "self-monitoring, analysis and reporting technology". In ATA-3 standard, S.M.A.R.T technology is formally established. The objects monitored by S.M.A.R.T include magnetic heads, disks, motors, circuits, etc. The monitoring circuit of the hard disk and the monitoring software on the host analyze and compare the running state of the monitored object with the historical record and the preset safety value, and will automatically warn the user when it exceeds the safety value range. More advanced technology can also remind network administrators to automatically reduce the speed of hard disk and transfer important data files. Through S.M.A.R.T technology, it can effectively predict the potential failure of hard disk and improve the security of data. However, we should also see that the S.M.A.R.T technology is not omnipotent, it can only monitor the gradual failures, and for some sudden failures, such as the sudden rupture of the disk, the hard disk is powerless. So in any case, backup is still necessary.

2.DFT technology

DFT(Drive Fitness Test) technology is a data protection technology developed by IBM for its PC hard disk. It uses DFT program to access DFT microcode in IBM hard disk to detect the hard disk, so that users can conveniently and quickly detect the running state of the hard disk.

According to research, most of the hard disks returned for repair by users are in good condition. DFT can reduce this situation, save time and energy for users and avoid data loss caused by misjudgment. It divides a separate space for DFT program on the hard disk, which can be called even if the system software can't work normally.

DFT microcode can automatically register error events and save the registered data in the reserved area on the hard disk. DFT microcode can also perform real-time physical analysis on the hard disk, such as reading servo position error signals, calculating disk exchange, servo stability, repetitive motion and other parameters, and giving graphs for users or technicians' reference. This is a brand-new concept, and the control signal of the hard disk subsystem can be used to analyze the mechanical condition of the hard disk itself.

DFT software is an independent software that does not depend on the operating system. When any other software of the user fails, it can run.

About extended partitions

Because the main partition table can only be divided into four partitions, which can not meet the demand, an extended partition format is designed. Basically, the information of extended partition is stored in the form of linked list, but there are some special places. First of all, there must be a basic extended partition entry in the main partition table, and all extended partitions belong to it. In other words, the space of all other extended partitions must be included in this basic extended partition. For DOS/Windows, the type of extended partition is 0x05. All the extended partitions except the basic extended partition are stored in the form of linked list, and the data items of the latter extended partition are recorded in the partition table of the previous extended partition, but the spaces of the two extended partitions do not overlap.

The extended partition is similar to a complete hard disk and must be further partitioned before it can be used. However, only one other partition can exist in each extended partition. This partition is a logical disk in a DOS/Windows environment. Therefore, the partition table of each extended partition (also stored in the first sector of the extended partition) can only have at most two partition data items (including the data items of the next extended partition).