A magnetic disk has 1000 cylinders, 10 tracks per cylinder, 128 sectors per track, 1 KB per sector. The rotation time is 6 msec, maximum seek time is 150 msec, switching between adjacent cylinders takes 15 msec, and switching between adjacent tracks within a cylinder takes no time. Assume this disk has 4 MB of data stored on it.If data is stored on consecutive tracks and is twice as likely to start on the first half (upper 5 tracks) of a cylinder than the second half (lower 5 tracks), find the average access timeSolution'#Tracks: 4 MB x 1024 KB/1 MB x 1 sector/1 KB x 1 track/128 sectors = 32 tracks Transfer time = 32 x 6 = 192 msecExp. switch and wait: Probability (twice as likely) -> If x = probability, 5 x 2x + 5 x 1x = 1 -> x = 1/15         Track  Probability   # switch s/w time           1     2/15               3               18x3            2     2/15               3               18x3           3     2/15               3               18x3           4     2/15               3               18x3           5     2/15               3               18x3           6     1/15               3               18x3           7     1/15               3               18x3           8     1/15               3               18x3           9     1/15               3               18x3          10     1/15               4               18x4        Exp. s/w = 5 x [(18x3) x 2/15] + 4 x [(18x3) x 1/15] + [(18x4) x 1/15] = 55.2 msec        Exp. access time = exp seek + exp latency + transfer + exp s/w = (1/3 x 150) + (1/2 x 6) + 192 + 55.2                = 300.2 msecIs there a easier method to this question maybe with formulas or something, 
magnetic Disk Calculation
mathematical foundations;filesystems