Calculating Hard Disk Read/Write Time & Capacity

[nerdygazilio]

Homework Statement

Suppose the hard disk above has 1024 cylinders, 8 tracks per cylinder, 32 sectors per track and 512 Bytes per sector. The maximum seek time is 450 msec, the time to move between adjacent cylinders is 10 msec, the rotation time is 14.

a) If the entire disk was full of data stored consecutively, how much time would it take to read the entire disk if the read/write head is already positioned on the first sector of the first track of the first cylinder of the disk?

b) Find the total capacity of the disk?

c) Find the maximum access time (worst case) for 800KB of data not stored on consecutive tracks. Clearly explain your solution/working.

Homework Equations

and

The Attempt at a Solution

1024 cylinders
8 tracks/ cylinder (8192 tracks)
32 sectors/ track (262144 sectors)
512 bytes/ sector (134217728 bytes)
Maximum seek = 450 ms
Switch/wait = 10ms + 4ms
Latency(rotational time) = 14 ms

a) Total time = number of tracks × rotational time
= 8192 tracks×14 ms
= 114688 ms


b) Total capacity = cylinders×tracks×sectors×512 bytes
= 1024 cylinders×8 tracks×32 sectors×512 bytes
= 134217728 bytes
= 134217728 bytes÷2^20
= 128 MBytes

c) Maximum access time = seek + latency + transfer + switch/wait

#tracks = (800×2^10 )bytes×(1 sector)/(512 bytes)×(1 track)/(32 sectors)
= 50 tracks

Transfer time = #tracks ×rotational time
= 50 tracks × 14 ms
= 700ms

Switch/ wait = 10ms +4ms = 14ms

Maximum access time = seek + latency + transfer + switch/wait
= 450ms+14ms+700ms+98ms
= 1262ms

 

[KataKoniK]

Explanation: The maximum access time for 800KB of data not stored on consecutive tracks is calculated by first determining the number of tracks needed to store the data, which is 50 tracks. Then, the transfer time for these tracks is calculated by multiplying the number of tracks by the rotational time of 14 ms. Next, the switch/wait time is added, which is 14 ms. Finally, the seek time and latency time are added to get the maximum access time of 1262 ms. This is the worst case scenario, meaning that the read/write head would have to move between the maximum number of cylinders and wait for the disk to rotate to the correct sector before accessing the data.