# How do wake timers work

sleepwake-up

Windows most commonly places a computer in S3 (standby/save-to-RAM) mode, where power is cut from the CPU but not to RAM.

If power is cut to the CPU, then how are wake timers triggered? Which component knows when to automatically wake the computer up?

If it is in the BIOS, how does Windows inform the BIOS of the next wakeup time?

The programming of these registers is done in the Linux kernel in cmos_set_alarm.