The total time for the data transfer (in milliseconds) from the hard disk is _________. (rounded off to one decimal place)
Calculating Hard Disk Data Transfer Time
The total time for data transfer from a hard disk is composed of three main components: Seek Time, Rotational Latency, and Data Transfer Time. We will calculate each component for the given scenario.
1. Seek Time Calculation
Seek time is the time taken by the read/write head to move to the correct track. The head moves between tracks sequentially.
- Initial position: Track 0
- Move to Track 5: From Track 0 to Track 5. Time = $ |5 - 0| \times 1 \, \text{ms} = 5 \, \text{ms} $.
- Move to Track 12: From Track 5 to Track 12. Time = $ |12 - 5| \times 1 \, \text{ms} = 7 \, \text{ms} $.
- Move to Track 7: From Track 12 to Track 7. Time = $ |7 - 12| \times 1 \, \text{ms} = 5 \, \text{ms} $.
- Total Seek Time = $ 5 \, \text{ms} + 7 \, \text{ms} + 5 \, \text{ms} = 17 \, \text{ms} $.
2. Rotational Latency Calculation
Rotational latency is the time taken for the desired sector to rotate under the read/write head. We use the average rotational latency for random accesses.
- Rotational Speed = 15000 rpm.
- Revolutions per second = $ \frac{15000}{60} = 250 \, \text{rps} $.
- Time for one full revolution = $ \frac{1}{250} \, \text{s} = 0.004 \, \text{s} = 4 \, \text{ms} $.
- Average rotational latency = $ \frac{1}{2} \times (\text{Time for one revolution}) = \frac{1}{2} \times 4 \, \text{ms} = 2 \, \text{ms} $ per sector access.
- Total number of sectors to access = 10 sectors/track $ \times $ 3 tracks = 30 sectors.
- Total Average Rotational Latency = 30 sectors $ \times $ 2 ms/sector = $ 60 \, \text{ms} $.
3. Data Transfer Time Calculation
Data transfer time is the time required to read the actual data from the sectors.
- Time for one full revolution = 4 ms.
- Number of sectors per track = 400.
- Time to transfer all sectors on one track = 4 ms.
- Time to transfer one sector = $ \frac{4 \, \text{ms}}{400 \, \text{sectors}} = 0.01 \, \text{ms/sector} $.
- Total number of sectors to transfer = 30 sectors.
- Total Transfer Time = 30 sectors $ \times $ 0.01 ms/sector = $ 0.3 \, \text{ms} $.
4. Total Data Transfer Time
The total time is the sum of seek time, average rotational latency, and data transfer time.
- Total Time = Total Seek Time + Total Average Rotational Latency + Total Transfer Time
- Total Time = $ 17 \, \text{ms} + 60 \, \text{ms} + 0.3 \, \text{ms} $.
- Total Time = $ 77.3 \, \text{ms} $.
The total time for data transfer, rounded to one decimal place, is 77.3 ms.
Important Questions from Secondary Memory
Which of the following can be said about primary storage in comparison with secondary storage?
__________ is the time taken to locate the disk arm to a specified track for data read/write.
For a magnetic disk with concentric circular tracks, the seek latency is not linearly proportional to the seek distance due to
If one track of data can be transferred per revolution, then what is the data transfer rate ?
Given below are two statements:
Statement I: The disk has a total number of 2000 cylinders.
Statement II: 51200 bytes is not a valid block size for the disk.
In the light of the above statements, choose the correct answer from the options given below:
