Power Management
To increase battery life, power management can be used to shut down portable computer components that do not need to run continuously. Most portable computers include power-saving modes that suspend the system operations when the computers are not in use. These power-saving modes are generally called suspend mode and hibernate.
Suspend Mode:
In Suspend Mode the entire system except the RAM is shut down after a certain period of inactivity. As
power is supplied to the RAM, the data contained in memory is retained and the portable computer
system can be reactivated almost immediately.
Hibernate Mode:
In Hibernate Mode the entire contents of memory is written to special swap file before the system is
completely shuts down. When the portable computer system is reactivated, the swap file is read back to
memory. The hibernate mode takes a little longer to reactivate than the suspend mode, but it conserves
more battery life.
There are currently two standards that define the interface between the power-management policy driver and the operating system,. The first is the Advanced Power Management (APM) standard which was jointly developed by Intel and Microsoft. This interface is usually implemented in the system BIOS. The second standard is called the Advanced Configuration and Power Interface (ACPI) and was developed Intel, Microsoft, and Toshiba. This standard places the power-management functions under the control of the operating system.