What is "fast startup"?

Hello, jaygourley

My name Is Alonso, I am an independent advisor.

Normally, when you turn off the computer, all the information in the RAM memory (both the operating system and the applications) that is stored in it is erased so that when you press the power button again, everything is reloaded from scratch , from the BIOS to the Windows Kernel and all the drivers.

With Windows 10 Quick Start, when you turn off your computer, the operating system closes all applications and processes that are running, and closes the session. However, instead of discarding all the information in RAM, Windows sends a message to the drivers that it is going into hibernation, copying part of the kernel and drivers to the hard disk.

When you turn your computer back on, instead of loading the entire operating system from scratch, the hibernated system is loaded directly into memory, so the login screen can be reached in less than half the time as if Windows would have had to boot from scratch. If you use a normal hard drive instead of an SSD, the time can be up to a tenth of the boot time.

I hope I have been helpful friend

Exactly my friend.

Thanks, AlonsoMoreno2_917.  If I understand correctly, it amounts to a kernel-only hibernation.  In other words, it's like hibernate except that all applications and processes are closed without storing.