That whirring you hear when you boot your computer or when it wakes from sleep mode is the sound of your hard drive’s magnetic disks beginning to spin. Conceptually not dissimilar to a record player, a hard disk drive (HDD) is an electromechanical device with an actuator arm that positions itself over spinning disks, called platters, in order to read or write information.
While record players top out at 78 rpm, today’s enterprise-grade HDDs can spin at 15,000 rpm. Even at that speed, however, there are unavoidable delays associated with heads finding the spot on the drive that contains the data being requested. And sometimes a drive may need to read from multiple locations in order to complete a command, multiplying wait times.