**硬盘**
相信很多人对硬盘的了解不多，特别是非计算机专业的朋友.我觉得有必要将硬盘的知识梳理一下，一来是巩固自己对硬盘的认识，二来是帮助不清楚硬盘的朋友了解硬盘.
硬盘分为机械硬盘、固态硬盘、混合硬盘(注：混合硬盘为机械硬盘与固态硬盘的结合体)，机械硬盘(HDD)造价低寿命长，固态硬盘(SSD)噪音小效率高.这里主要讲解机械硬盘.
硬盘其实是由许多的盘片、机械手臂、磁头与主轴马达所组成的，如下图所示：
Our data is actually written on a disc with a magnetic substance. Reading and writing are mainly done through the reading head on the robotic arm. In actual operation, the spindle motor makes the disc rotate, and then the robotic arm can be extended for reading The head reads and writes on the disk. In addition, due to the limited capacity of a single disk, some hard disks have more than two disks inside. The
most basic component of the hard disk is made of hard metal material. Discs with magnetic media, the number of discs with different capacities varies. Each disc has two sides and can record information. The entire disc seems to have a pie chart drawn by multiple concentric circles, and the center of the disc is radial The smallest storage unit of the disk is divided into sectors. Each sector can store 128x2 to the second power, which is 512 bytes. Concentric circles with different radii are called tracks. In a hard disk, different disks are composed of tracks with the same radius. The cylinder is called cylinder.
Sectors, cylinders, and magnetic heads constitute the basic parameters of the hard disk structure. The calculation formula of hard disk capacity is: storage capacity = number of heads x number of cylinders x number of sectors per track x 512bytes. (Note: number of tracks = Number of cylinders) When
general hard disk manufacturers describe the capacity of hard disks, most of them are calculated in decimal. Therefore, a 500G hard disk on the market will actually only have a capacity of about 460G. The
hard disk interface is divided into three types IDE interface, SATA interface, SCSI interface. The hard disk is mainly accessed by the spindle motor rotating the disk, so the speed of the speed directly affects the performance. The mainstream desktop computer hard disk is 7200 rpm, and the notebook is 5400 rpm. The hard disk contains A buffer memory is mainly used to cache data frequently used by the hard disk to accelerate the read performance of the system, because the speed of reading from the buffer memory is much faster than reading directly from the hard disk.
Note, the content of the article is optional From Brother Bird's book on Linux explanations and network friends' explanations on hard drives.