How to Calculate Average Disk Read Time

Hard disk performance has a major effect on overall system performance.

The hard disk performance is one of the most important aspects when it comes to the speed of your system. Moreover, a very slow disk read time will always affect the performance of other components of the system as well. When computing the disk read time, a number of factors should not be missed, such as the speed of rotation, the size of the sector to be read and the average seek time for the device.

Instructions

1. Find out the average seek time of your hard disk. You can use the manufacturer's website for this purpose, or just search online for this specific information. In this example, assume this value is 5ms.

2. Estimate the usual transfer rate of your hard disk. You can do this by moving files between different locations on your local disk. Drag a large file from one location on the drive to another. Take note of the transfer rate, which is displayed in the transfer window, once the rate stabilizes. For the sake of this example, suppose the transfer rate is 10MB/s.

3. Decide upon the size of the sector to be read. Take a 512 byte sector for this example.

4. Find the controller time of your hard drive. As in step 1, you can also use the Internet to search for the information. In this example, use 2ms.

5. Search for the speed of rotation of your hard drive. If, for example, your disk is rotating at 7200 RPM, it will take around 8.4ms to perform a rotation. However, on average, only half a rotation is part of the waiting time, so 4.2ms will be used in this example instead.

6. Add up all the values to obtain the average disk read time. Considering the values mentioned above, the following result is obtained: 5ms (average seek time) + 4.2ms (rotation speed) + 0.03 (0.5 KB / 15MB) + 2ms (controller time) = 11.23ms.

References

• CS162 - Operating Systems and Systems Programming: Lecture 17: Disk Management and File Systems; Joseph, Anthony
• jact.ac.il: Disk Read Time