Does the OS always stay with the hard drive?

[SizedMouse9]

I am trying to create a list for a new gaming pc around $1200-$1400 and was wondering if I replace all my parts except the hdd, will windows 10 stay on it? But I am also thinking of getting an ssd but dont know where the OS is supposed to go or if I should switch it to the ssd.
If I get the ssd will I have to buy a new OS and put it on the ssd?

Here is the list, make any comments or suggestions: https://pcpartpicker.com/list/Y2B3zM

 

[TJ Hooker]

The actual OS installation, yes. Although it's usually a good idea to reinstall the OS upon changing mobos anyway. Also, your Windows license is usually tied to your motherboard. If you link your Win10 license to an MS account it should transfer over if you use that account in the new build, otherwise you may have to call MS to activate Win10 on your new build.

 

[mazboy]

If you change everything but the HDD that the OS is on, it is unlikely that the computer will boot or run well. Win10 doesn't like when you do that. Rather than try to do it, get the SSD, assemble the computer (without the old HDD connected), load the OS onto the SSD, and make sure the computer runs properly before connecting the old HDD. The computer will always boot from the SSD, but you will have access to your old data on the HDD.

But the best thing to do would be to back up your data on the HDD, and after getting your computer running off of the new SSD, install the old HDD and format it so it is empty again, and you can begin using it like it were a new drive.