Abstract: A method for controlling a rotating disk magnetic data storage device employing several reduced power modes which are automatically entered and exited under the control of the rotating disk device microcontroller. Two modes are provided which are fully responsive to host computer commands, and are thereby transparent to the host computer user, all providing significant power savings. An additional full power down mode is provided which can be initiated by a command from the host computer user, wherein the operational state parameters of the rotating disk device are stored in the host computer until the host computer powers on the device. At this time the stored state parameter are restored into the rotating disk device allowing it to resume its operational state immediately prior to the power suspension.