osher :
What's the difference between M.2 SSD and normal SSD?
Also, I want to buy a hard drive for gaming and use the SSD for Windows.
so I want to buy SSD to use it only for Windows and use a normal hard drive for gaming.
can I do that?. And if I could, should I?
Yes you can do that. I have a SSD for windows and programs, SSD for games, SSD for a scratch drive, 2 HDD for storage and work, 2 HDD for backup.
For what your using the PC for their no reason to buy a M.2 SSD their no real performance difference you will notice about a 0.5 second faster boot time for about double the price of a SATA SSD.
You install the SSD and install Windows and the drivers, then install the HDD, format it and assign it a drive letter (C drive is default for your OS drive) Then you can load your games on the HDD. Make a folder on the HDD called games or something and when it ask you where to download the game pick where that folder is. (games and the drive letter you picked for it)