A. Portable computers that support APM (Advanced Power Management) will have the ability to go into standby mode.
While on standby, your entire computer switches to a low power state where devices, such as the monitor and hard disks, turn off and your computer uses less power. When you want to use the computer again, it comes out of standby quickly, and your desktop is restored exactly as you left it. Standby is particularly useful for conserving battery power in portable computers. Because Standby does not save your desktop state to disk, a power failure while on Standby can cause you to lose unsaved information so its best to save any open documents before going into standby.
A small amount of power is still used as the machine is not totally turned off as it has to maintain the memory state so any programs running when put in standby will still be active.
To put your machine in standby mode manually select 'Stand by' from the shutdown menu. Some portables will also support tapping the power button which will also but in suspend mode rather than powering off but check the manual.
You can also configure the machine to automatically go into standby or hibernate after x minutes using the Power Options control panel applet.