Most portable computers include power-saver modes that suspend system operations when the computers are not in use. Different manufacturers have different names for their power-saver modes such as: suspend, hibernate, or conserve, but they all usually refer to two different states of power conservation: one state continues to power the system's RAM, while the other does not.
Generally, the suspend mode virtually shuts down the entire system after a certain period of inactivity. However, power continues to be supplied to RAM, and the system can be reawakened almost immediately.
The hibernate mode writes the entire contents of memory into a special swap file and then shuts down the system. When reactivated, the file is read back to memory. The hibernate mode takes a little longer to reactivate than the suspend mode, but conserves more battery life. In some systems, the swap file used for the hibernate mode is located in a special partition of the hard drive. If it is inadvertently destroyed, it might require a special utility from the manufacturer to re-create it.
A document jointly developed by Intel and Microsoft-known as the Advanced Power Management (APM) standard-has been, for the most part, responsible for defining the interface (interaction) between the power-management policy driver and the operating system. This interface is usually implemented in the system BIOS.
Another standard currently under development by Intel, Microsoft, and Toshiba is called the Advanced Configuration and Power Interface (ACPI). This standard is designed to place the power-management functions under the control of the operating system. As power-management techniques develop, it becomes difficult for the BIOS to maintain the complex information states needed to run the more advanced functions. Placing power management under the control of the operating system allows applications to interact with the operating system to let it know which of its activities are crucial and which can wait until the next time the hard disk drive is activated.
