Technical indicators of hard disk performance

Technical indicators of hard disk performance, including hard disk capacity, hard disk speed, hard disk rotation speed, interface, cache, hard disk single disk capacity, etc.

Hard Disk Interface

ATA, the full name of Advanced Technology Attachment, uses a traditional 40-pin parallel port data cable to connect the motherboard and hard disk. The maximum external interface speed is 133MB/s. , because the anti-interference performance of the parallel port cable is too poor, and the cable takes up space, which is not conducive to computer heat dissipation, it will gradually be replaced by SATA.

IDE

The full English name of IDE is "Integrated Drive Electronics", which is "electronic integrated drive", commonly known as PATA parallel port.

SATA

Hard drives using the SATA (Serial ATA) port are also called serial hard drives and are the future trend of PC hard drives. In 2001, the Serial ATA Committee composed of major manufacturers such as Intel, APT, Dell, IBM, Seagate, and Maxtor officially established the Serial ATA 1.0 specification. In 2002, although Serial ATA related equipment has not yet been officially launched, Serial ATA The ATA committee has taken the lead in establishing the Serial ATA 2.0 specification. Serial ATA uses a serial connection method. The Serial ATA bus uses an embedded clock signal and has stronger error correction capabilities. Compared with the past, its biggest difference is that it can check the transmission instructions (not just data). If Errors are automatically corrected when found, which greatly improves the reliability of data transmission. The serial interface also has the advantages of simple structure and support for hot swapping.

SATA2

Seagate adds NCQ local command array technology to SATA and increases the disk speed.

SCSI stands for Small Computer System Interface. It has gone through many generations of development, from the early SCSI-II to the current Ultra320 SCSI and Fiber-Channel. There are also different types of connectors. Various. SCSI hard drives are widely used in workstation-level personal computers and servers because they rotate quickly, up to 15,000 rpm, and consume less CPU computing resources during data transmission. However, the unit price is also more expensive than ATA and SATA hard drives of the same capacity.

SAS (Serial Attached SCSI) is a new generation of SCSI technology. Like SATA hard drives, it adopts serial technology to obtain higher transmission speeds, which can reach 3Gb/s. In addition, the internal space of the system is improved by reducing the connection cables.

In addition, since SAS hard disks can share the same backplane as SATA hard disks, in the same SAS storage system, SATA hard disks can be used to replace some expensive SCSI hard disks, saving overall storage costs.

Hard drive size

5.25-inch hard drive; used in desktop computers in the early days, has withdrawn from the stage of history.

3.5-inch desktop hard drive; very popular and widely used in various computers.

2.5-inch notebook hard drive; widely used in notebook computers, desktop all-in-one machines, mobile hard drives and portable hard drive players.

1.8-inch micro hard drive; widely used in ultra-thin laptops, mobile hard drives and Apple players.

1.3-inch micro hard drive; single product, Samsung's unique technology, only used in Samsung's mobile hard drives.

1.0-inch micro hard drive; first developed by IBM, MicroDrive micro hard drive (MD for short). Because it complies with CFII standards, it is widely used in SLR digital cameras.

0.85-inch micro hard drive; single product, Hitachi’s unique technology, known to be only used in one HD mobile phone from Hitachi.

The physical structure of the hard disk

1. Magnetic head

The internal structure of the hard disk The magnetic head is the most expensive component of the hard disk, and also The most important and critical part of hard disk technology. The traditional magnetic head is an electromagnetic induction head that combines reading and writing. However, reading and writing on a hard disk are two completely different operations. For this reason, the design of this two-in-one magnetic head must take into account both reading and writing. These two characteristics have resulted in limitations in hard drive design. MR heads (Magnetoresistive heads), that is, magnetoresistive heads, use a separated magnetic head structure: the write head still uses a traditional magnetic induction head (MR heads cannot perform writing operations), and the read head uses a new MR head. The so-called inductive writing and magnetoresistive reading. In this way, the different characteristics of the two can be optimized separately during design to obtain the best read/write performance. In addition, the MR head senses the signal amplitude through resistance changes rather than current changes, so it is very sensitive to signal changes, and the accuracy of reading data is also improved accordingly. And since the read signal amplitude has nothing to do with the track width, the track can be made very narrow, thereby increasing the disk density to 200MB/inch2, while using traditional magnetic heads can only reach 20MB/inch2. This is also the case with MR heads. The main reason why it is widely used. At present, MR magnetic heads have been widely used, and GMR magnetic heads (Giant Magnetoresistive heads) made of materials with a multi-layer structure and better magnetoresistive effect are also gradually becoming popular.

2. Track

When the disk rotates, if the heads remain 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 just magnetized areas on the disk that are magnetized in a special way. The information on the disk is stored along such tracks. Adjacent tracks are not immediately adjacent to each other. This is because when the magnetized units are too close to each other, the magnetism will affect each other, and it will also make it difficult for the magnetic head to read and write. A 1.44MB 3.5-inch floppy disk has 80 tracks on one side, while the track density on a hard disk is much greater than this, usually with thousands of tracks on one side.

3. Sector

Each track on the disk is divided into several arc segments. These arc segments are the sectors of the disk. Each sector The area can store 512 bytes of information. The disk drive uses sectors as the unit when reading and writing data to the disk. 1.44MB 3.5-inch floppy disk, each track is divided into 18 sectors.

4. Cylinder

Hard disks are usually composed of a set of overlapping platters. Each disk is divided into an equal number of tracks, and starts from the outer edge. Numbering starts with "0", and tracks with the same number form a cylinder, which is called the cylinder of the disk. The number of cylinders on a disk is equal to the number of tracks on a disk. Since 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 is Cylinder (cylinder), Head (head), and Sector (sector). As long as the number of CHS of the hard disk is known, the capacity of the hard disk can be determined. The capacity of the hard disk = number of cylinders * number of heads * Number of sectors*512B.

The logical structure of the hard disk

1. Hard disk parameter explanation

So far, the hard disk parameters that people often talk about are still The ancient CHS (Cylinder/Head/Sector) parameters. So why are these parameters used? What is their meaning? What is their value range?

A long time ago, when the capacity of the hard disk was still very small, people used a structure similar to that of a floppy disk to produce hard disks. That is, each track of the hard disk platter has the same number of sectors. This resulted in the so-called 3D parameters (Disk Geometry). They are the number of heads (Heads), the number of cylinders (Cylinders), the number of sectors (Sectors), and the corresponding addressing methods.

Among them:

The number of heads (Heads) indicates how many heads the hard disk has in total, that is, how many platters there are, the maximum is 255 (stored in 8 binary bits);

The number of cylinders (Cylinders) indicates the number of tracks on each side of the hard disk, with a maximum of 1023 (stored in 10 binary bits);

The number of sectors (Sectors) indicates the number of tracks on each track Several sectors, the maximum is 63 (stored with 6 binary bits);

Each sector is generally 512 bytes. Theoretically, this is not necessary, but it seems that there is no other value. .

So the maximum disk capacity is:

255 * 1023 * 63 * 512 / 1048576 = 7.837 GB (1M =1048576 Bytes) or the unit commonly used by hard disk manufacturers:

255 * 1023 * 63 * 512 / 1000000 = 8.414 GB (1M =1000000 Bytes)

In the CHS addressing mode, the value range of the head, cylinder, and sector is 0 to Heads - 1.0 respectively. To Cylinders - 1. 1 to Sectors (note starting from 1).

2. Introduction to basic Int 13H call

BIOS Int 13H call is the disk basic input and output interrupt call provided by BIOS, which can complete the disk (including hard disk and floppy disk) Reset, read and write, verification, positioning, diagnosis, formatting and other functions. It uses the CHS addressing method, so it can access a hard disk of about 8 GB at maximum (unless otherwise specified in this article, the unit is 1M = 1048576 bytes).

3. Introduction to modern hard disk structure

In old hard disks, since the number of sectors in 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 (same as floppy disks). In order to solve this problem and further increase the hard disk capacity, people switched to using equal density structure to produce hard disks. 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 method is also changed to linear addressing, that is, addressing in units of sectors.

In order to be compatible with old software that uses 3D addressing (such as software that uses the BIOSInt13H interface), an address translator is installed inside the hard disk controller, which is responsible for translating the old 3D parameters into new linear parameters. . This is also the reason why there are many choices for the 3D parameters of hard disks now (different working modes correspond to different 3D parameters, such as LBA, LARGE, NORMAL).

4. Introduction to Extended Int 13H

Although modern hard disks have adopted linear addressing, due to the constraints of the basic Int13H, programs using the BIOS Int 13H interface, For example, DOS can only access hard disk space within 8 G. In order to break this limitation, several companies such as Microsoft have developed the Extended Int 13H standard (Extended Int13H), which uses linear addressing to access the hard disk, thus breaking the 8G limit, and also adding support for removable media (such as movable media). hard drive) support.

Basic parameters of hard disk

1. Capacity

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

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

The capacity index of the hard disk also includes the single disk capacity of the hard disk. The so-called single disk capacity refers to the capacity of a single hard disk platter. The larger the single disk capacity, the lower the unit cost and the shorter the average access time.

For the user, the capacity of the hard disk is just like the memory, there will always be too little and not too much. In addition to simpler operations, the Windows operating system has also brought about the increasing size and number of files. Some applications can easily consume hundreds of megabytes of hard disk space, and there is a trend of continuous increase. . Therefore, it is wise to be appropriately advanced when purchasing a hard drive. In the past two years, the mainstream hard drive has been 80G, and large-capacity hard drives above 160G have also begun to become more popular.

Generally speaking, the larger the hard disk capacity, the cheaper the price per byte, but there are slight exceptions for hard disks that exceed the mainstream capacity. As of early December 2008, the price of a 1TB (1000GB) Seagate hard drive in Zhongguancun was RMB 700, and a 500G hard drive was about RMB 320.

2. Rotation speed

Rotation speed (Rotationl Speed ​​or Spindle speed) is the rotation speed of the motor spindle in the hard disk, which is what the hard disk platter can rotate in one minute. Maximum number of revolutions completed. The speed of rotation is one of the important parameters that indicates the grade of the hard disk. It is one of the key factors that determines the internal transmission rate of the hard disk and directly affects the speed of the hard disk to a large extent. The faster the hard disk rotates, the faster the hard disk searches for files, and the relative transmission speed of the hard disk is also improved. The hard disk speed is expressed in revolutions per minute, and the unit is RPM. RPM is the abbreviation of Revolutions Per minute, which is revolutions per minute. The larger the RPM value, the faster the internal transfer rate, the shorter the access time, and the better the overall performance of the hard drive.

The spindle motor of the hard disk drives the platter to rotate at high speed, generating buoyancy to make the magnetic head float above the platter. To bring the sector of data to be accessed under the head, the faster the rotation speed, the shorter the waiting time. Therefore, the rotational speed determines the speed of the hard drive to a large extent.

The speeds of ordinary hard drives for home use generally include 5400rpm and 7200rpm. High-speed hard drives are also the first choice for desktop users; while for notebook users, 4200rpm and 5400rpm are the main ones, although some companies have released 7200rpm. notebook hard drives, but they are still relatively rare in the market; server users have the highest requirements for hard drive performance. SCSI hard drives used in servers basically use 10,000 rpm, and even 15,000 rpm, and their performance is much higher than that of household products. Higher rotational speed can shorten the average seek time and actual read and write time of the hard disk. However, as the hard disk rotation speed continues to increase, it also brings negative effects such as temperature increase, increased motor spindle wear, and increased operating noise. The rotation speed of laptop hard drives is lower than that of desktop hard drives, which is partly affected by this factor. The internal space of the notebook is small, and the size of the notebook hard drive (2.5 inches) is also designed to be smaller than the desktop hard drive (3.5 inches). The temperature rise caused by the increase in rotation speed puts higher requirements on the heat dissipation performance of the notebook itself; the noise becomes louder. , and necessary noise reduction measures must be taken, which puts more requirements on notebook hard drive manufacturing technology. At the same time, the increase in rotational speed, while keeping other things unchanged, means that the power consumption of the motor will increase, the more electricity will be consumed per unit time, and the working time of the battery will be shortened, which will affect the portability of the notebook. Therefore, laptop hard drives generally use relatively low-speed 4200rpm hard drives.

The speed changes with the improvement of hard disk motors. Now fluid dynamic bearing motors (Fluid dynamic bearing motors) have completely replaced traditional ball bearing motors. Liquid bearing motors are usually used in the precision machinery industry. They use mucous membrane liquid oil bearings, using oil films instead of balls. This can avoid direct friction on the metal surface, minimizing noise and temperature; at the same time, the oil film can effectively absorb vibration, improving the earthquake resistance; it can also reduce wear and extend service life.

3. Average Access Time

The average access time (Average Access Time) refers to the time when the magnetic head reaches the target track position from the starting position and finds the desired location from the target track. The time required to read and write data sectors.

The average access time reflects the read and write speed of the hard disk, which includes the seek time and waiting time of the hard disk, that is: average access time = average seek time average waiting time.

The average seek time of a hard disk (Average Seek Time) refers to the time required for the hard disk's head to move to a specified track on the disk surface. Of course, the smaller the time, the better. Currently, the average seek time of hard disks is usually between 8ms and 12ms, while SCSI hard disks should be less than or equal to 8ms.

The waiting time of the hard disk, also called latency, refers to the time it takes for the magnetic head to be on the track to be accessed and waiting for the sector to be accessed to rotate under the magnetic head. The average waiting time is half of the time it takes for the disc to rotate once, and should generally be less than 4ms.

4. Transmission rate

Transfer rate (Data Transfer Rate) The data transfer rate of the hard disk refers to the speed at which the hard disk reads and writes data. The unit is megabytes per second (MB/s). The hard disk data transfer rate also includes internal data transfer rate and external data transfer rate.

Internal Transfer Rate (Internal Transfer Rate) is also called the Sustained Transfer Rate (Sustained Transfer Rate), which reflects the performance of the hard disk buffer when it is not used. The internal transfer rate mainly depends on the rotation speed of the hard drive.

External Transfer Rate is also called Burst Data Transfer Rate or interface transfer rate. It is nominally the data transfer rate between the system bus and the hard disk buffer. , the external data transfer rate is related to the hard disk interface type and the size of the hard disk cache.

The current maximum external transfer rate of Fast ATA interface hard disk is 16.6MB/s, while the Ultra ATA interface hard disk reaches 33.3MB/s.

Hard drives using the SATA (Serial ATA) port are also called serial hard drives and are the future trend of PC hard drives. In 2001, the Serial ATA Committee, composed of major manufacturers including Intel, APT, Dell, IBM, Seagate, and Maxtor, formally established the Serial ATA 1.0 specification. In 2002, although Serial ATA related equipment has not yet been officially launched, the Serial ATA Committee has taken the lead in establishing the Serial ATA 2.0 specification. Serial ATA uses a serial connection method. The Serial ATA bus uses an embedded clock signal and has stronger error correction capabilities. Compared with the past, its biggest difference is that it can check the transmission instructions (not just data). If Errors are automatically corrected when found, which greatly improves the reliability of data transmission. The serial interface also has the advantages of simple structure and support for hot swapping.

Serial hard disk is a new type of hard disk interface that is completely different from parallel ATA. It is famous for its use of serial method to transmit data. Compared with parallel ATA, it has many advantages. First of all, Serial ATA transmits data in a continuous serial manner, and only 1 bit of data is transmitted at a time. This can reduce the number of pins in the SATA interface, reduce the number of connecting cables, and be more efficient. In fact, Serial ATA can complete all the work with only four pins, which are used to connect cables, connect ground wires, send data, and receive data. At the same time, this architecture can also reduce system energy consumption and reduce system complexity. Secondly, Serial ATA has a higher starting point and greater development potential. The data transfer rate defined by Serial ATA 1.0 can reach 150MB/s, which is higher than the highest data rate of 133MB/s that the fastest parallel ATA (i.e. ATA/133) can achieve. The transfer rate is still high, and the data transfer rate in Serial ATA 2.0 reaches 300MB/s. Eventually, SATA will achieve a maximum data transfer rate of 600MB/s.

5. Cache

Cache (Cache memory) is a memory chip on the hard disk controller. It has extremely fast access speed. It is the internal storage and storage of the hard disk. Buffer between external interfaces. Since the internal data transmission speed of the hard disk is different from the external interface transmission speed, the cache plays a buffering role. The size and speed of the cache are important factors directly related to the transmission speed of the hard disk, and can greatly improve the overall performance of the hard disk. When the hard disk accesses fragmented data, it needs to continuously exchange data between the hard disk and the memory. If there is a large cache, the fragmented data can be temporarily stored in the cache, reducing the load on the external system and increasing the data transmission speed.

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