Hybernate/sleep vs normal shutdown & boot?

Hibernating and sleeping the computer stores everything on the hard disk, then moves everything back to memory, including the state the CPU was in, etc. The operating system doesn't need to load into RAM or anything.

Turning the computer off then rebooting requires the operating system to load into memory, set up user variables, and register everything, including all devices, all hardware (RAM, hard disks, printers, monitors, CPUs, etc., etc.), and that takes time for each and every item to register itself.

Again, when you wake up a computer from hibernation or sleep mode, nothing has to register, nothing has to load - a "snapshot" of RAM and CPU status that was stored in the HD is simply restored, just as if nothing ever happened.

When the computer is put into sleep mode it just powers down everything except the memory, that way when you power it up again it just carries on from where it left off. If you hibernate it then it saves the processor registers and memory contents to the hard drive, when it starts again it just loads these back in again and then carries on from where it was like before. However, when it starts up or reboots it has to load up Windows from scratch, configure the hardware and start various programs running, this takes time as it involves hundreds of separate tasks.