Shulou(Shulou.com)06/03 Report--

In this issue, the editor will bring you a physical unit about what is a disk read and write operation. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

The physical unit in which the disk reads and writes is: the sector. The operating system reads / writes to the disk in sectors, which are the smallest physical units in which the disk stores information.

The sector refers to the area divided on the disk. Each track on the disk is equally divided into several arc segments, which are the sectors of the disk, and the read and write of the hard disk is based on the sector.

Each side of the disk is divided into many tracks, that is, some concentric circles on the surface, and the closer to the center, the smaller the circle.

And each track is divided into sectors by 512 bytes, called sectors. In the parameter list of some hard drives, you can see the parameters that describe the number of sectors per track, which is usually identified by a range, such as 373 sectors. This means that the outermost track has 746 sectors, while the innermost track has 373 sectors, so it can be calculated that the track capacity is from 186.5KB to 373KB (190976B--381952B).

The disk drive reads and writes data to the disk in sectors.

On disk, the DOS operating system allocates disk space to files in "clusters". The cluster of a hard disk is usually multiple sectors, depending on the type of disk, the DOS version, and the size of the hard disk partition.

Each cluster can only be occupied by one file, even if there are several bytes in this file, never allow more than two files to share a cluster, otherwise it will cause data confusion.

This mechanism with clusters as the minimum allocation unit makes it relatively easy for the hard disk to manage data, but it also causes a waste of disk space, especially in the case of a large number of small files, a large hard disk with a large number of gigabytes. the wasted disk space can reach hundreds of megabytes.

In order to find and manage sectors, sectors need to be numbered, starting with track 0, starting with 1 sector, followed by 2 sectors and 3 sectors. After the sector number of track 0 ends, the starting sector of track 1 accumulates the number until the last sector of the last track (n sector).

For example, if a hard disk has 1024 tracks, each of which is divided into 63 sectors, the sector number of track 0 is 1x63, the starting sector number of track 1 is 64, and the last sector number of the last track is 64512.

There are some differences between hard disk and floppy disk in sector numbering. In a track of floppy disk, the sector number is arranged at once, that is, 1, 2, 3. N sector. Due to the high rotational speed of the hard disk, the magnetic head must transfer the data to the microcomputer after reading and writing data from a certain sector, which takes a time, but at this time the hard disk continues to rotate at a high speed, and when the data transmission is completed, when the magnetic head reads and writes the second sector, the disk has been rotated to another sector. Therefore, in the early hard disk, the sector number was arranged according to a certain interval coefficient jump.

The above is the physical unit of disk read and write operations shared by the editor. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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