Assume that a hard disk has the following characteristics:Rotation speed = 7200 rev/minArm movement time = 0.5 msec fixed startup time+ 0.05 msec for each track crossed. (The startup time is a constant no matter how far the arm moves.) Number of surfaces = 2 (This is a double-sided disk. A single read/write arm holds both read/ write heads.)Number of tracks per surface = 500Number of sectors per track = 20Number of characters per sector = 1024a. How many characters can be stored on this disk?b. What are the best-case worst-case and average-case access times for this disk?