softoff

Softoff, in the context of electronics and computing, refers to a software-controlled shutdown state in which the system powers down most active circuitry while leaving a minimal level of standby power available to detect wake events. It is commonly associated with the soft-off state defined by modern power-management standards.

In the ACPI framework, soft-off corresponds to the S5 state. When an operating system initiates a shutdown, the system transitions to this state, appearing off to the user. Although most components are powered down, a small amount of power continues to flow to the chipset or other standby circuitry to monitor for wake signals, such as a power button press or configured wake events. This enables the system to be restarted without a full power cycle.

Implementation involves coordinated action between the operating system, firmware (BIOS or UEFI), and hardware. The OS flushes data to non-volatile storage as part of a proper shutdown, and the firmware places the machine into a low-power configuration. Once in soft-off, the vast majority of circuits are inactive, reducing energy consumption while preserving the ability to wake quickly.

Soft-off is distinct from sleep states (where memory remains powered) and from a complete hard power-off that removes all residual power. It is also differentiated from hibernation, which saves the system state to disk and then powers down without keeping memory active. Soft-off is widely used in desktop and laptop computers to provide a safe, software-controlled shutdown with rapid reactivation capabilities.