powerstate

Power state is a designation for the operational condition of an electronic device or system with respect to its power consumption and its ability to function. It is used to manage energy use, temperature, and performance, while balancing responsiveness and data integrity. Power states can apply to individual components (such as CPUs, disks, or network interfaces) as well as to whole systems (such as computers or virtual machines).

In computing hardware and operating systems, power states are often formalized for energy management. A common framework is ACPI, which defines sleep-like states such as S0 (fully on and active), and S1 through S3 as progressively deeper low-power sleep modes. S4 represents hibernation, where the system state is saved to nonvolatile storage and the device powers down, and S5 denotes a soft-off condition. Not all systems expose every state, and transitions between states are influenced by hardware capabilities, user settings, and software policies.

In virtualization, power state refers to the status of a virtual machine. Typical states include powered on (the VM is running), powered off (the VM is shut down), and suspended or saved (the VM’s state is preserved in memory or on disk and can be resumed later). Management tools use these states to schedule resources, perform migrations, or perform controlled shutdowns.

Devices in software and firmware environments may have power states such as D0 (fully on), D3 (off or minimal functionality) and intermediate levels (D1, D2) that describe the device’s readiness and wake-up requirements. Efficient power state design aims to minimize energy use while meeting performance and reliability needs, considering wake latencies, data retention, and user expectations.