Fast Startup (called Fast Boot in Windows 8) works similarly to the hybrid sleep mode of previous versions of Windows. By saving the operating system state to a hibernation file, it can make your computer boot up even faster, saving valuable seconds every time you turn your machine on.
Fast Startup combines elements of a cold shutdown and the hibernate feature. When you shut down your computer with Fast Startup enabled, Windows closes all applications and logs off all users, just as in a normal cold shutdown. At this point, Windows is in a state very similar to when it’s freshly booted up: No users have logged in and started programs, but the Windows kernel is loaded and the system session is running. Windows then alerts device drivers that support it to prepare for hibernation, saves the current system state to the hibernation file, and turns off the computer.
When you start the computer again, Windows does not have to reload the kernel, drivers, and system state individually. Instead, it just refreshes your RAM with the loaded image from the hibernation file and delivers you to the login screen. This technique can save considerable time off your start up.
In this video demo you can learn how to enable “Fast Startup” in Windows 10.