Originally Posted by kumaiti
If it is identical to shuting down completely AND will come back faster (in other words: it has two advantages and no disvantage as you put), why isn't it the default action used by the operational system? Are you sure there is no con of using Hibernate??
Hibernate is a process where the contents of RAM are written to the hard drive, then the computer shuts down physically, can be unplugged, battery removed, stored for ten years, etc.
When the computer reboots, the OS (WindowsXP) recognizes the existence of the hibernated condition and rather than loading Windows, it loads the previous RAM contents stored on the hard drive back into RAM and comes back to life exactly where you left off. Everything you were doing on your PC before you shut down are exactly the way you left it including open documents, web pages, applications, etc. You may continue working is if you never shut down. The time required to hibernate (on or off) is dependent on the amount of RAM on your system and the performance of your hard drive. i.e. it takes longer to write 2GB to the hard drive than 256MB. It is almost always significantly quicker to start from hibernate than a full system reboot.
Sleeping is different, and a much faster process. The contents of RAM are maintained in RAM by keeping power on the system but with reduced requirements. The optical drives and hard drives are shut down and the heads parked so it is safe to move the equipment. The overall system power is reduced to very low amounts so the cooling fans can often shut down completely. The graphics system is also shut down and if the monitor is complient it will also automatically enter standby mode to reduce power. When you "wake up" the computer it comes back to life in mere seconds, depending on the system, since nothing has to be loaded into RAM.
If you encounter problems with sleep or hibernate it is likely there are issues with the hardware or the operating system. Each componenet in the system has to be set up properly to sleep and the wake conditions have to be set. For example, an installed modem may be set to never go to sleep or to wake the system everytime it detects a phone call. A network card may also be configured incorectly. The BIOS on the motherboard may not be compatible with sleep mode in WindowsXP if it is an older system or it may simply not be set up right. If you build your own system these are issues you need to personally deal with. If you buy a pre-built system with a pre installed OS it should be set up properly by the manufacturer.
One thing to remember with sleep or hibernate is that any conditions in your OS that exist prior will still be there such as memory leaks, failed applications that are hanging, etc. If your OS is running smoothly you should not have any issues.