And besides all that, hibernate is fundamentally more complex than sleep. With sleep, when waking up the computer resumes directly to the already loaded operating system in RAM, and the operating system "only" has to restore all the hardware state. With hibernate, the computer does a clean boot of a fresh copy of the operating system, which has to initialize all hardware, read the hibernation image, de-initialize (quiesce and/or power off) all hardware, and finally jump to the copy of the operating system found in the hibernation image, which only then will restore all hardware state.