In a magnetic disk, a cylinder is
options:
1) the number of concentric tracks on the disk.
2) the number of concentric tracks on one surface.
3) the number of blocks on one track.
4) the amount of data that can be transferred without moving the head.
The correct answer and explanation is:
The correct answer is 2) the number of concentric tracks on one surface.
In a magnetic disk, a cylinder refers to the set of all tracks at a given position across all disk surfaces. Each track is a concentric ring on the surface of the disk where data is stored. The cylinder is created by aligning these tracks vertically across all surfaces of the disk. When a read/write head moves to a specific track on one surface, the other read/write heads positioned on different surfaces (but at the same radial position) also align with the corresponding tracks, forming a cylinder. This is why the number of concentric tracks on one surface is referred to as a cylinder.
The number of tracks on a disk can vary depending on the number of surfaces and the disk’s design. Typically, a disk has multiple platters (disk surfaces), each of which can have its own set of tracks. A single cylinder, therefore, is made up of tracks that are directly aligned vertically on each platter. The read/write head does not need to move radially to access different tracks within the same cylinder, which allows data to be read or written more efficiently.
This definition of a cylinder is crucial when discussing disk geometry, as it helps understand how data is organized and accessed. Each cylinder can be accessed without moving the head radially across the disk, thus reducing seek time, which is the time it takes for the read/write head to position itself over the correct track. This efficiency is key to improving the overall performance of the disk when accessing data spread across multiple tracks and surfaces.