What is the difference between "sleep" and "hibernate" ?
That's a good question. Windows has several different power-saving states that trade off the amount of power savings against how long it takes for the computer to turn back on, and whether power is required.
Sleep turns on quickest, but has the lowest power savings and requires some power to keep the computer going. I routinely let my computers go into sleep state after 15-30 minutes of inactivity. It takes a couple seconds for the computer to restart from this state.
Hibernate completely* turns the computer off, but supports faster restart than a cold boot because the running state of programs is saved at the time of hibernation. Depending on your computer it can take 10-30 seconds or more to return from hibernate, based in part on how much memory you have and how many programs you have running.http://windows.microsoft.com/en-us/wind ... -questions
provides more detail on the tradeoffs.
Windows 8 has some big improvements in this area, primarily with a feature called "hybrid sleep". That combined with a SSD (flash) drive gives excellent startup performance. Most Windows 8 computers are configured to use hybrid sleep instead of shutdown, meaning the system only reboots (in the classic sense) for certain driver and update installations.
If you have slow hibernate or resume times, this article
points you to the section of the event log that will show which driver on your computer is slowing things down. Slow hibernate/resume times are often due to third party drivers taking a long time to start/shut down.