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In Windows 8, is there a difference between:

Shutting down my computer (inside W8) and then instantly turn it back on again
Restarting it from inside Windows 8

Edit: Talking about normal Windows 8 desktop (not RT).
Edit2: Reason for asking is that shutting down and turning on my computer did not fix something where I needed a reboot, but a Restart did. I've heard that when shutting down the kernel is hibernated, but not when doing a restart.

What are the implications of doing one instead of another. When do I need to do one instead of the other?

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Would you like to share the objective of your experiment? That way people would be better able to advise. For me, shutdown gives a chance for the electrical / mechanical parts to stop completely. – Guy Thomas Nov 20 '12 at 10:28
@GuyThomas thanks for your reply. Updated my question. – Matsemann Nov 20 '12 at 13:45
@Matsemann: Thank You!!! Searching upon it coldbooted my info repository too... :D – Viral Jain Dec 3 '12 at 3:50
up vote 20 down vote accepted

Straight from Microsoft Blog:

Here’s the key difference for Windows 8: as in Windows 7, we close the user sessions, but instead of closing the kernel session, we hibernate it. Compared to a full hibernate, which includes a lot of memory pages in use by apps, session 0 hibernation data is much smaller, which takes substantially less time to write to disk. If you’re not familiar with hibernation, we’re effectively saving the system state and memory contents to a file on disk (hiberfil.sys) and then reading that back in on resume and restoring contents back to memory. Using this technique with boot gives us a significant advantage for boot times, since reading the hiberfile in and reinitializing drivers is much faster on most systems (30-70% faster on most systems we’ve tested).

Use of multiple cores: It’s faster because resuming the hibernated system session is comparatively less work than doing a full system initialization, but it’s also faster because we added a new multi-phase resume capability, which is able to use all of the cores in a multi-core system in parallel, to split the work of reading from the hiberfile and decompressing the contents. For those of you who prefer hibernating, this also results in faster resumes from hibernate as well.

Shutdown+TurnOn≡ColdBoot: Another important thing to note about Windows 8’s fast startup mode is that, while we don’t do a full “Plug & Play” enumeration of all drivers, we still do initialize drivers in this mode. Those of you who like to cold boot in order to “freshen up” drivers and devices will be glad to know that is still effective in this new mode, even if not an identical process to a cold boot.

And this point is worth mentioning regarding your Edit2 where shutdown+trunOn didn't fix your problem, but Restart did:

When to use Restart specifically: Of course, there are times where you may want to perform a complete shutdown – for example, if you’re opening the system to add or change some hardware. We have an option in the UI to revert back to the Windows 7 shutdown/cold boot behavior, or since that’s likely a fairly infrequent thing, you can use the new /full switch on shutdown.exe. From a cmd prompt, run: shutdown /s /full / t 0 to invoke an immediate full shutdown. Also, choosing Restart from the UI will do a full shutdown, followed by a cold boot.

More extended info, visit: Delivering fast boot times in Windows 8

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This explains why my computer boots extremely slow and uses loads of memory on start: The computer has 64GB Ram and SQL Server uses 50+GB - after a normal shutdown the boot process loads the 50GB into memory, which takes 10-20 minutes. And, of course, after reboot the 50gb ram are used. – Sam Sep 8 '15 at 18:28

Yes, there is a difference.

Shutdown will place the kernel in a "hybrid hybernation" mode, so it won't be loaded fully on the next boot, and you will have a faster boot.

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Hey, I have experienced that shut-down & corresponding boot is visibly faster over even Win7, but still won't a Restart be faster than shut-down & boot cycle? Given the span of time, we cannot ignore the time consumed to switch on the computer back again by pressing the button ... & I'm serious here... – Viral Jain Nov 20 '12 at 9:14
A restart is slower because it won't use the hybrid hybernation mode, and will load everything again – Magnetic_dud Nov 20 '12 at 13:25
I've explained the new startup here: If this is slow, check this topic on how to use xbootmgr to see cause of the slowness:… To answer your question about why reboot fixed an issue. Rebooting means compete reinitialization of devices, drivers, registry and all tools are started again, which the new shutdown only suspends and resumes the drivers/services. This is the important difference! After you've installed new tools always make a reboot. – magicandre1981 Nov 20 '12 at 14:41
Have you tried, or has anyone mentioned Fast startup? To turn off Fast Startup, seek the Power Options in the Control Panel. Start with 'Choose what the power buttons do'. Remember to 'Change settings that are not currently available'. Remove the tick next to 'Turn on fast startup' – Guy Thomas Nov 20 '12 at 15:35

You can turn on/off this under Power option→choose what the power buttons do→chnge settings that are currently unavailable and mark/unmark the Turn on fast startup option

What is fast startup?

Fast startup is a setting that helps your PC start up faster after shutdown. Windows does this by saving system info to a file upon shutdown. When you start your PC again, Windows uses that system info to resume your PC instead of restarting it.

What is the difference among shutdown, full shutdown and restart?

Simple shutdown saves the session in hibernation mode and when you turn back it on it just loads what you want.
A proper shutdown is doing in Windows 8 by using shutdown /s from run dialog or from command line.

While a reboot will followed by a full shutdown with "cold boot".

When do I need to do one instead of the other?

Obviously when you need a fast startup then you have choose the shutdown option from charm bar. But if you need a reboot then you have to shut it down using shutdown /s command. Also shutdown /r will restart the computer with full shutdown.

You need a full shutdown in case when you have made changes in policies(sometime) or a new hardware.

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While a reboot will followed by a full shutdown with "cold boot" Is that cold boot or warm boot..? I thought it is warm boot.. – Ramesh-X Jun 14 at 9:46

The fast start up setting doesn't apply to Restart. but what is fast start up? you can see below link for detail information about a windows 8 technology called Fast Start up (aka: hybrid boot or hybrid Shutdown)

Delivering fast boot times in Windows 8

but how to disable it, simply if you disable hypernation hybrid bood has been disabled and startup, restart shutdown works like windows 7:

1 - Open an Elevated Command Prompt.

2 - In the elevated command prompt, type:

powercfg -h off

and press Enter.

3 - Close the elevated command prompt.

4 - restart windows.

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To do a "normal" shutdown without the need of special command lines (or icons), you can hold down the Shift key while clicking the shutdown text over power off menu.
In response to the main question, yes, default shutdown is realy an ibernation.

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