RPM stands for "Rotations Per Minute". It is a measurement term for how many times the circular platter on a disk drive can complete a 360-degree rotation per minute.

Because hard drives must spin to access and transfer data, a higher RPM hard drive can access and transfer data faster.

During operation, higher RPM is noticeable when starting new programs that force the computer to access the hard drive, or when transferring and writing large amounts of data to the hard drive.

A hard drive's RPM will have less impact on the computer's running speed after a program is started, as the data needed for faster access will be saved in the computer's RAM.