Disk structure
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Platter: A disk has multiple platters;
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Track: A circular band-shaped area on the disk surface. A disk surface can have multiple tracks;
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Track Sector: An arc on a track. A track can have multiple sectors. It is the smallest physical storage unit and currently has two sizes: 512 bytes and 4 K;
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Head: It is very close to the disk surface and can convert the magnetic field on the disk surface into an electric signal (reading), or convert the electric signal into a magnetic field on the disk surface (writing);
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Actuator arm: used to move the magnetic head between tracks;
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Spindle: Rotate the entire disk surface.
Disk scheduling algorithm
The influencing factors of the time to read and write a disk block are:
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Rotation time (the spindle rotates the disk surface to make the head move to the appropriate sector)
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Seek time (braking arm moves to make the head move to the appropriate track)
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Actual data transfer time
Among them, the seek time is the longest, so the main goal of disk scheduling is to make the average seek time of the disk