Disks are a very interesting matter of hardware to look at; especially the magnetic disk, in which a magnetic polarity is given to be able to store data including pictures, sound…etc the disk mechanism is simple, a disk that revolves around its axis, and a header that is relatively stationary. In relatively stationary I mean it only moves to the inside of the disk to the outside; changing the track it is reading.

As you might know the length of an arc on a circle is defined by the following:

Length of an arc = angle in radians * radius

Thus one may infer an inner track has a shorter length because the radius is shorter than that track on an outer track. (The circumference is the same the angle is 360 degrees or 2 pi radians) thus one would expect that an outer track would have more blocks or bits if they were packed as a tightly as the inner track. A problem occurs if this method is used if the disk is rotating at a constant speed because the head read/writes more bits on the outside than the inside when rotating the same angle. To fix this problem the outer blocks are packet loosely; meaning the number of bits on an inner block is equivalent to the number of bits on an outer block. This mechanism uses what is called a “constant angular velocity” in which the disk spins a certain angle (say 2pi in radians of course) at the same speed.

This fixes the problem; however it is not so efficient because you are wasting disk space, in the literal sense. If you pack the bits tightly together, using all the disk space you increase the efficiency of the use of the disk but then you would need the disk to rotate at different speeds on each track. This mechanism uses a constant linear velocity in which the head travels over a specific distance or arc length in a given time. The problem that arises here is how would the disk motor know what speed is necessary at which track.  This loses its efficiency in that you need to know where you are on the disk to be able to spin the disk at the required speed. To solve this problems some disks use zoning. In which each zone has a specified speed. This is like a common ground for not wasting as much “disk space” and not having to go through the hassle of figuring out the required disk speed on every track.