What is cylinder ?

What is cylinder ? How many cylinder = 1MB or 1 gbytes ?
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Well, in a hard drive, there are several platters (or independent disks) with two sides usable sides to each (on newer drivers).  Each platter is divided into concentric rings called tracks (as on a cd or vinyl album).  If you look at the outer track on the top of the first platter, each surface of each platter below it has a matching track.  These together forma a cylinder.  Similarly, each progressive track towards the center of the platters form progressivly smaller cylinders.  In the old days, the tracks were divided into sectors, each one being the same size in bytes.  Each track, no matter ho large (distance from center) had the same capacity and same number of tracks.  In those days, it would be easy to answer your question.  However, now, in an effort to maximize space on a disk, they are now using LBA mode, which is logical block addressing.  This method does not rely on sectoring.  Likewise, each track/cylinder contains a different amount of data proportional to its size.  You will have to refer to your drive's manufacturer website for specifications.  The newer drives can be set up with cylinders and sectors instead of LBA mode, but some amount of space is wasted with this method.  

More specific to your question, as you can see, the more platters in your disk, and the more tightly packed the data on the cylinders, the fewer cylinders are required for a GB.  It really depends on the disk and the storage scheme.

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