电源选项中S1，S2，S3，S4，S5的含义 以 ACPI 的規格來說吧！

S1 ⇒Standby。即指說系統處於低電源供應狀態，在 windows or BIOS 中可設定螢幕訊號輸出關閉、硬碟停止運轉進入待命狀態、電源燈號處於閃爍狀態。此時動一動滑鼠、按鍵盤任一鍵均可叫醒電腦。

S2 ⇒Power Standby。和 S1 幾乎是一樣。

S3 ⇒Suspend to RAM。即是把 windows 現在存在記憶體中的所有資料保存不動，然後進入「假關機」。此時除了記憶體需要電源來保持資料以外，其它的設備、裝置全部停止供電。也就是說，理論上可以把 CPU, PCI, AGP device 拿掉又插回去，電腦也可能正常完成開機及運作，只要不動到記憶體和電源的部份。這時只剩下電源燈號一閃一閃的，其它和關機沒什麼兩樣。（電源供應器的風扇也停止運轉喔）重新開新後，電腦只是把記憶體的資料完整性確認後，即立刻會回到你進 S3 前的畫面。記得有人試過，在燒錄中啟動 S3 ，CDRW 還會自動啟動 Just-Link ，等你回復後它又自動繼續燒。（聽說而以，自己沒試過）。

S4 ⇒Suspend to Disk。即是把 windows 記憶體中的資料完整的存在硬碟中。等開機時就直接從存這些資料的地方直接完整的讀到記憶體，不需要跑一堆應用程式。使用這種模式的話，硬碟一定要騰出一個完整的連續空間。Windows 98/SE 必需要用軟體去製作一個大檔案或是一個磁區來提供 win98/SE 執行 S4 這功能，WinME/2000/XP 本身就有製作一個大檔案來給 S4 功能用（在電源管理中有一個啟動休眠，就是這個啦） 。在啟動後，在 C: 下會看到一個和你電腦現有記憶體大小一樣的大檔案。

S5 ⇒Shutdown….這不用說了吧！

S1/S3 在 windows 中都叫「待命 or standby」，所以在 BIOS 裏會有一個選項，設定說 Standby mode 為何，是要 S1 還是 S3，所以啦。S1 和 S3 是不能同時存在的。不是 S1,S4,S5 就是 S3,S4,S5 。

Sleep States S1 - “Stopgrant” Power to cpu is maintained, but no instructions are executed. The CPU halts itself and may shut down many of its internal components. In Microsoft Windows, the “Standby” command is associated with this state by default.

S2 While defined in the spec, this state is not currently in use. It resembles S3 with the qualification that some devices are permitted to remain on.

S3 - “Suspend to RAM” All power to the cpu is shut off, and the contents of its registers are flushed to RAM, which remains on. In Microsoft Windows, the “Standby” command can be associated with this state if enabled in the BIOS. Because it requires a high degree of coordination between the cpu, chipset, devices, OS, BIOS, and OS device drivers, this system state is the most prone to errors and instability. Pavel Machek has created a small document with some hints how to solve problems with S3. You can find it in the kernel sources at Documentation/power/tricks.txt. S3 is currently _not_ supported by the 2.4.x kernel series in Linux.

S4 - “Suspend to Disk” CPU power shut off as in S3, but RAM is written to disk and shut off as well. In Microsoft Windows, the “Hibernate” command is associated with this state. A variation called S4BIOS is most prevalent, where the system image is stored and loaded by the BIOS instead of the OS. Because the contents of RAM are written out to disk, system context is maintained. For example, unsaved files would not be lost following an S4 transition. S4 is currently _not_ supported by the 2.4.x kernel series in Linux, but you might have good luck with SWSUSP. Some machines offer S4_BIOS whose support is considered to be experimental within Linux/ACPI.

S5 - “Soft Off” System is shut down, however some power may be supplied to certain devices to generate a wake event, for example to support automatic startup from a LAN or USB device. In Microsoft Windows, the “Shut down” command is associated with this state. Mechanical power can usually be removed or restored with no ill effects.