A device with an autonomous sleep characteristic, which is in communication with a host, is described. The device includes one or more communication subsystems. Each communication subsystem maintains a sleep activity indicator that indicates whether a corresponding communication subsystem is allowed to go to sleep. Each communication subsystem can autonomously enter a sleep state, when its sleep activity indicator indicates that the corresponding communication subsystem is, in fact, allowed to go to sleep. The device also includes a controller. The controller has a block memory which stores data written to the device from the host. The controller further includes a sleep state indicator that indicates a sleep state of each communication subsystem.