# How to Calculate the Average Latency of a Disk Drive

By G.S. Jackson

For platter-style hard drives, latency is an issue. "Latency" is the term used to denote the lag in time between a request for information from the disk drive and the disk drive's readiness to return that information. Because disk platters have to spin to a certain location, or "sector," before the disk can retrieve the information on that platter, there is a possible down time of a few milliseconds during data requests. Using a simple formula, the programmer can determine an average latency for a hard drive.

## Step 1

Check the model number from the hard drive, either in drive's documentation or by physically looking at the hard drive in the case. Often, the model number appears on a sticker attached to the case of the hard drive.

## Step 2

Find out the spindle speed through the vendor's website. You can determine specifications on Samsung model hard drives, for example, by looking up the model number on the Samsung website. Spindle speed is usually given in rotations per minute.

## Step 3

Use the following formula to determine average latency for that specific hard drive. This example calculates latency for a hard drive with 6,000 RPM:

(1 / (SpindleSpeed / 60)) * 0.5 * 1000 = (60/6000) * 500 = 500/100 = 5 milliseconds