What is “Fast” Startup doing?

I‘ve recently (3 Oct ‘20) completed the Win7 –> Win10 migration (whilst the jury’s still out on whether I consider it an upgrade I’ll confess it’s going much better than feared) and am familiarizing myself with the changed environment. One thing that’s puzzling me is Fast Startup. Given the lack of consensus found on the net regarding the value of Fast Startup I ran some tests to satisfy my curiosity. My methodology was to (a) turn off AV, (b) shutdown from cmd window (shutdown /s /f /t 0) and (c) run vbs script with different scenarios:


The second Fast Startup UNchecked is because I was so startled at the first run having the same reboot time as Fast Startup checked. Apparently the most charitable thing that can be said – based on these observations – about the impact of Fast Startup on boot/reboot times is that it’s negligible at best.

What is Fast Startup doing since it doesn’t actually seem to have anything to do with starting up? Is it integral to some other function (?sleep, maybe?) or is it marketing trivia I can safely ignore?

Short answer.....

If you have an SSD as your boot drive, Fast Startup is basically frivolous. If your boot drive is an HDD, you will see a measurable difference.

Fast Startup actually does it's prep work on Shutdown. It writes system files in memory and other static data to hiberfil.sys on the drive. Then, at boot time from a start up reads that instead of search around the drive looking for all the pieces. It can cause more problems than it's worth. It's required for Hibernation type sleep mode, otherwise turn it off and forget it.

Just read your sys specs. In your case, Fast Startup can, should be, off. No advantage whatsoever. Only thing is if you want to Hybrid Sleep, it must be on. Other than that, ditch it. When OFF, you will regain ~4-6GB of SSD space. When it is ON, you will have several GB of writes to your SSD on shutdown. More unnecessary wear and tear on the SSD cells.

I know you've bounced around the web reading about it, but this is a good explanation in tech layman terms, meaning not too techy, but not 1st grade.

The Pros and Cons of Windows 10’s “Fast Startup” Mode

Fast startup is pointless if you have a SSD. Fast start up options in the BIOS can also cause problems.