How is the speed of a hard drive measured?

The speed of a hard drive is primarily measured in revolutions per minute (RPM). This metric indicates how many times the platters inside a hard disk drive spin in one minute. A higher RPM generally allows for quicker data access and retrieval times, as the read/write heads can access data more frequently. For instance, common RPM values for hard drives are 5400 RPM and 7200 RPM, with the higher figure typically providing better performance.

In contrast, while the data transfer rate and megabits per second are associated with how quickly data can be moved, they are not direct indicators of the hard drive's inherent speed characteristics as determined by RPM. Storage capacity, on the other hand, refers to the total amount of data a drive can hold and does not reflect its operational speed. Thus, RPM stands out as the most relevant and common measure used to evaluate a hard drive's speed.