SuspendtoRAM

SuspendtoRAM is a low-power sleep state in which the system’s main memory (RAM) remains powered and retains its contents while most other components are powered down or placed in low-power modes. In this state, the CPU is paused and most peripherals are disabled; the system can be awakened by input devices, network activity, timers, or other wake events. The term is often written as suspend-to-RAM or abbreviated S3, and it is contrasted with suspend-to-disk (hibernation).

Implementation and operation vary by platform, but suspend-to-RAM is typically realized through ACPI’s S3 sleep state. The operating system initiates a suspend request, devices are quiesced, and firmware puts the platform into S3. On resume, the firmware performs wake-up and the OS restores execution from RAM. In Linux, suspend-to-RAM can be triggered via commands such as systemctl suspend or by echoing mem to /sys/power/state; the kernel’s power management (PM) framework coordinates device suspension, RAM retention, and resuming. The mem_sleep_default kernel parameter can influence which sleep state is preferred by default on wake.

Compatibility and considerations: S3 support depends on hardware, firmware, and drivers. Some systems use alternate sleep states or do not support suspend-to-RAM at all, opting for hibernation or hybrid sleep; virtual machines typically do not expose real RAM-based suspend. Reliability of suspend-to-RAM improves with proper BIOS/firmware support and up-to-date drivers. While it offers fast resume and lower sustained power than a powered-on state, a fault during suspend or resume can lead to data loss in RAM, and increased RAM refresh activity can slightly increase standby power in some configurations.