What's sleep mode?

Sleep mode is your pc's operations are suspended, to save power. it hibernates till you take it to WAKE UP!

I'll have to keep an eye on this discussion because I've never been able to figure this out either! I've had a pc for years and have never intentionally used the sleep mode but have noticed they do it on their own sometimes.

Sleep Mode shuts down the power to the monitor and transfers data to RAM before shutting down the disk drives, so no programs will be running during this period. The idea is that energy is conserved and the computer can be restarted without the need to boot up from cold. The same principle applies to Hibernation, except that the data is transferred to the hard drive rather than to RAM. The problem with either of these systems is that too often the system is reluctant to wake up and you may end up having to manually switch off the computer to restart it.

It is basically a Mode wherein a Computer is not at its full Operational Mode but is not off either -i.e a kind of Power Saving Mode .