Notes a file system, disk physical structure
Introduction: file system fundamentally speaking, is abstract and dress up the operating system on the disk by. Therefore, knowledge of the physical structure of the disk, are the basis of our study of the file system.
First, the introduction of the concept of disk
And the code data from the main memory required for running computer (memory). If the computer is not running, the data and code which is stored in it? Memory is not a persistent storage medium, it is the process of processes running in the temporary storage space allocated. Once the process is running over, its share of the memory space is released, stored will be lost inside the code and data. Therefore, data and long codes in order to save , you need a more permanent place to store, this place is stored in the disk .
For most people, the computer field, is often seen as an external disk device. Available for modern operating systems in terms of disk is indispensable. Earlier operating systems can be based on the tape, with the operating system complexity and performance rising, outdated tape as a carrier of the operating system, it replaced the disk. Because the operating system needs to be stored on the disk, and the disk files within the operating system is mainly based. Therefore, the disk is an integral part of the operating system .
Second, the disk definition
Popular terms, the disk is shaped like a plate of magnetic storage media , such properties are permanent storage medium , the above data is present under normal circumstances will not disappear; magnetic, round its salient features, so called disk; cost inexpensive and can be widely used. For the modern computer, the disk has become an indispensable component.
Hard disk (English: Hard Disk Drive, referred to as HDD) is to use a hard disk based on the rotation of the non-volatile computer storage device that data on a flat surface of the magnetic storage and retrieval of digital information by the magnetic head close to the magnetic surface from , to change the flow by the electromagnetic polarities are written to disk electromagnetic current, the information can be read by a reverse manner. A hard disk including the number of sheets to the high speed rotation of the magnetic disk and the magnetic head is placed on the boom actuator. - Wikipedia
Third, the disk structure
3.1, external structure
Learn the definition of the disk, and now we want from outside to inside, simple to understand the structure and how it works disk. From the outside, the structure includes a metal disk fixed panel, three parts of the control board and the electric connector.
Metal mounting panel : there will always be a metal disk external panel to protect the entire hard disk, usually affixed to the front of their product labels, labeling the product type, origin, parameters , etc. This information is based on the proper use of basic disks. Metal panels and the bottom plate sealed into one whole, to ensure stable operation of the disk.
The control circuit board : the metal cover of the disk will be fixed to a circuit board, the circuit board is disk drive circuit board. To save space, the general welding SMD components, these components consisting of different electronic function of the electronic circuits, which comprises a spindle speed control circuit, a drive head, positioning servo motor, read and write circuit, and a control interface circuit . There are several main circuit board of the chip: the master chip, the BIOS chip, the cache chip, a motor driver chip.
Interface : In the top there will be several different hard disk drive interface, these interfaces include power socket interface , data interface , the master jumper from the interface . Wherein the main power socket and is connected to the power supply, provides power to work hard to ensure. Data interface and the data is hard for quality control board link circuit switched transmission. Middle of the main, the jumper from the disk interface to the hard disk from a master set, i.e., set the hard disk drive access order.
3.2, the internal structure
Open the disk enclosure, its internal structure at a glance. The internal structure of a disk assembly including a magnetic head, a magnetic head drive assembly, with the disk spindle assembly and the pre-control circuit.
Magnetic head assembly : the head assembly includes a read-write heads of three parts, the drive arm shaft composition. The most important part is the head, the other two can be regarded as part of the head support device. Drive shaft drive transmission arm, the head reaches the developing position. In operation the disk, a head to read data by sensing changes in the magnetic field rotation on the disk, data is written by the magnetic field change on the disk . To avoid wear of the head and the disk, in working condition, the magnetic head floating above the platter, only 0.1 -0.3um gap.
Head drive assembly : head movement is driven by component implementation , and the length of time and find a head disk drive components are closely related. Capable of high-precision head drive mechanism for driving the magnetic head and the correct positioning, and the positioning system can accurately track the instruction designated in a short time, to ensure the reliability of data read and write.
Disk and spindle assembly : the carrier disc is a hard disk for storing data, the next section will focus on presentation. Spindle assembly includes a spindle drive motor and the other pad member. With the expansion of hard drive capacity and speed, spindle motor speed is improving.
- Pre control circuit : a signal control circuit amplifies the pre-induced in the magnetic head , the spindle motor speed, and head positioning servo positioning, since the head reads the signal is weak, the amplifier circuit may be sealed within the cavity of the external signal to reduce interference, increase the accuracy of the operation instructions.
3.3, the disk structure
A hard disk for storing data carriers. A disk is actually not only a piece of the disc, but by multiple platters, the pros and cons of each disc can store all the data. On each disk it is equipped with a read-write head, and all the read-write head attached to a shared magnetic arm. When the disk arm movement, the heads are all doing the same movement. Places disk constant speed spinning. This rotation speed is typically from 3,500 to 10,000 revolutions per minute, i.e., approximately every one rotation 6ms to 17ms. (Case 10000, 10000 rpm / min, i.e., 10,000 rpm consumed 1 * 60 * 1000 = 60000ms)
To facilitate data storage, people will each disk is divided into tracks and sector .
Tracks : a track is a concentric circle. When the disk rotates, if it is stored in a head position, the head will each draw a circular path on the disk surface, the circular path is called a track. Typically one surface of the disc there are thousands of tracks, the disk along the track above information is stored, but between adjacent tracks at a distance, to avoid magnetic interaction when the magnetization unit is similar.
Sector : each side of each disk are divided into many concentric tracks, but also each concentric circle is further divided into a plurality of equal arc, which is arcuate sectors (also called sector). Data then stores sector, the sector is the smallest unit of disk I / O operations. Sector typically contains a title, data, ECC error correction information, which includes the synchronization title and location information, ECC function is to provide error detection and correction of the data segment.
- Cylinder : a plurality of disk drives typically composed, and each surface is divided into an equal number of tracks, and numbered starting from the outer edges (i.e. the edges of the track is most track 0 are sequentially entered accumulation). Track thus with the same number of tracks will form a cylinder, the cylinder is called the cylinder. Number of cylinders of the disk and the number of tracks on a disk are equal.
Summary: The disk is persistent non-volatile storage medium, characterized by a circular magnetic. Understand its physical structure, have enabled us to learn the contents of the file system.
Cenkaoziliao:
"Philosophy Caozuoxitong of" Zou Hengming the
Wikipedia, the physical structure of the disk of
Baidu - hard physical structure and how it works
