Estados de energia do sistema
Para o usuário, o sistema parece estar ativado ou desativado. Não há outros estados detectáveis. No entanto, o sistema suporta vários estados de energia que correspondem aos estados de energia definidos na especificação Advanced Configuration and Power Interface (ACPI). A tabela a seguir lista os estados de energia do maior para o menor consumo de energia.
Working
S0
The system is fully usable. Devices that are not in use can save power by entering a lower power state.
Sleep
S1
S2
S3
The system appears to be off. Power consumption is reduced to one of several levels, depending on how the system is to be used. The lower the level of power consumption, the more time it takes the system to return to the working state.
Hibernation
S4
The system appears to be off. Power consumption is reduced to the lowest level. The system saves the contents of memory to a hibernation file, preserving the state of the operating system, applications, and open documents.
Soft Off
S5
The system appears to be off. Some components remain powered so the computer can wake from input from the keyboard, LAN, or a USB device. The working context can be restored if it is stored on nonvolatile media.
Mechanical Off
G3
The system is completely off and consumes no power. The system returns to the working state only after a full reboot.
Mais aqui:
ACPI / Gerenciamento de energia - Suporte a arquitetura e drivers