Glossary:
- Track: concentric ring on disk
- Cylindrical: all concentric rings with the same radius form a cylindrical
- Sector: The track is divided into small segments along the radius line. Each segment is called a sector.
- Seek: Move the head to the target track
- Rotation: rotate the disk to rotate the target sector to the bottom of the head.
- Locality Principle: when a piece of data is used, the nearby data is usually used immediately.
- Page: the page is the logical block for the computer to manage the memory. The hardware and operating system usually divide the primary storage and disk storage areas into contiguous blocks of the same size, each block is called a page (the page size is usually 4 KB)
- Disk prefetch: Read data of a certain length from the target location into the memory (the pre-read length is generally an integer multiple of the page)
- Disk Directory: the disk directory maps the Logical Data address to the corresponding physical sector address.
- Disk I/O time: data transmission time + disk directory read time + seek time + rotation time
Disk location: the operating system transmits the Logical Address of the data to the disk. the disk first reads the disk directory to determine the address of the physical sector of the data. Then, locate the head to the target track by seeking the track, and position the target sector to the bottom of the head by rotating. In this case, you can access the data on the disk through the head. When the disk reads data, it performs disk prefetch based on the local principle.
