Understanding Disk Data Transfer Rate Calculation

The question asks us to calculate the data transfer rate of a disk drive based on its specifications. The data transfer rate is the speed at which data can be read from or written to the disk. It is typically measured in bytes, kilobytes, or megabytes per second.

We are given the following relevant information:

• Sector size: 512 bytes
• Sectors per track: 50
• Transfer condition: One track of data transferred per revolution

The other specifications like tracks per surface, number of platters, and seek time are not directly needed for calculating the data transfer rate under the given condition of transferring one track per revolution.

Calculating Data Per Track

First, we need to determine how much data is stored on a single track. A track consists of multiple sectors, and we know the size of each sector and the number of sectors per track.

Data per track = Number of sectors per track $\times$ Sector size

Data per track = $50 \text{ sectors/track} \times 512 \text{ bytes/sector}$

Data per track = $25600 \text{ bytes/track}$

To express this in Kilobytes (KB), we divide by 1024 (since 1 KB = 1024 bytes):

Data per track = $25600 \text{ bytes} / 1024 \text{ bytes/KB}$

Data per track = $25 \text{ KB/track}$

Relating Transfer to Revolutions

The question states that one track of data is transferred per revolution. This means that the time it takes to transfer one track is equal to the time it takes for the disk to complete one full rotation (one revolution).

Calculating Time Per Revolution

The time per revolution is determined by the rotation speed of the disk, usually measured in Revolutions Per Minute (RPM). If the disk spins at RPM revolutions per minute, then the number of revolutions per second is RPM / 60. The time taken for one revolution is the reciprocal of this value.

Time per revolution = $\frac{1}{\text{Revolutions per second}}$

Time per revolution = $\frac{1}{\text{RPM } / 60} = \frac{60}{\text{RPM}} \text{ seconds}$

Calculating Data Transfer Rate

The data transfer rate is the amount of data transferred divided by the time taken to transfer it. Since one track is transferred per revolution, the data transfer rate is the data per track divided by the time per revolution.

Data Transfer Rate = $\frac{\text{Data per track}}{\text{Time per revolution}}$

Data Transfer Rate = $\frac{25 \text{ KB}}{60 / \text{RPM } \text{ seconds}}$

Data Transfer Rate = $25 \times \frac{\text{RPM}}{60} \text{ KB/second}$

The options provided are numerical values for the data transfer rate. Let's see which standard RPM value would yield one of the options. Common RPM values for hard drives include 5400, 7200, 10000, etc.

Let's test RPM = 5400:

Data Transfer Rate = $25 \times \frac{5400}{60} \text{ KB/second}$

Data Transfer Rate = $25 \times 90 \text{ KB/second}$

Data Transfer Rate = $2250 \text{ KB/second}$

This calculated rate of 2250 KBytes/second matches one of the provided options.

Conclusion

Based on the calculation using a standard disk speed of 5400 RPM, the data transfer rate is 2250 KBytes/second.

Revision Table: Disk Drive Concepts

Additional Information: Factors Affecting Disk Performance

While the question focused on data transfer rate per revolution, other factors significantly impact overall disk performance:

• Seek Time: Moving the read/write heads is often the slowest part of accessing data, especially for random access. Average seek time is an important performance metric.
• Rotational Latency: Waiting for the desired sector to spin under the head adds to the access time. Higher RPM reduces rotational latency.
• Controller Overhead: The disk controller also adds some delay in processing requests.
• Interleaving: The arrangement of sectors on a track can affect the effective transfer rate. With 1:1 interleaving, consecutive sectors are arranged sequentially, allowing potentially faster continuous reads.
• Cache/Buffer: Disk drives often have a built-in cache memory that stores frequently accessed data, improving performance.
• Interface Speed: The speed of the interface connecting the disk drive to the computer (e.g., SATA, SAS) can be a bottleneck for data transfer, especially for fast drives.

The data transfer rate calculated here ($2250 \text{ KB/second}$) represents the maximum instantaneous rate for reading a continuous track once the head is positioned. Actual performance in a system can be lower due to seek time, latency, and controller overhead.