What is Difference between shutdown (power off) and restart (reboot) ?
What type of signals passing at time of reboot and poweroff, to where ?
What is difference between these two signals ?
At the time of reboot,
Is the operating system go to shutdown mode ?
If it goes shutdown, Which is make it to start again ?
Please correct it, if you find and mistakes in my questions
For the operating system, shutdown and reboot are practically the same thing.
The OS will shut down as usual in both cases. The only difference is the signal sent to the hardware at the very last moment.
To switch off/reboot the computer, the OS will send a special signal to the hardware once it is finished shutting down. It's only this signal which will be different between a reboot and a shutdown.
The way the signal is sent depends on the exact hardware platform. On modern systems it is usually done via ACPI.
Go to https://en.wikipedia.org/wiki/Reboot
You may also find this article helpful:
https://en.wikipedia.org/wiki/Booting
While the accepted answer is generally true there is "Windows quick-start" under Windows-10 and Windows Server 2016 a setting which is making booting faster as per ninjaone by:
"[...] saving an image of the loaded Windows kernel and drivers into the hiberfile (hiberfil.sys) before a computer shuts down. Upon [booting], Windows uses this image to speed up the boot time[...]
Meaning that there is now a difference between manually shutting down & booting again vs using the "restart" option. Which in turn may cause issues. But it can be disabled:
- Navigate to the Control Panel and select ‘Power Options.’
- Choose ‘Choose what the power buttons do.’
- Click on ‘Change settings that are currently unavailable.’
- Under ‘Shutdown settings,’ uncheck the ‘Turn on fast startup’ box.
As for Windows 11 the feature is also available as per Howtogeek, you should go to Control Panel > System and Security > Power Options > "Change What the Power Buttons Do" and then:
On the following page, at the top, click "Change Settings That Are Currently Unavailable." Then, enable [or disable as needed] the "Turn On Fast Startup (Recommended)" option and choose "Save Changes."
The article also states:
One thing to note when enabling this feature is that not all your Windows updates will properly install when shutting down. This is because Fast Startup doesn't fully shut down and turn on your machine. For those occasions, reboot your PC instead of shutting it down, and your updates will install without issues.
The difference is that during reboot system is entering runlevel 6 and for shutdown it is runlevel 0.
It is similar to running
init <runlevel_number>
For more details on runlevels see https://en.wikipedia.org/wiki/Runlevel
Under /etc/rc<runlevel_number>.d/ (e.g. /etc/rc6.d/) directories you will find script executed on entering specific runlevel.
