Thanks. It's just about if I need to buy a new SSD with 120gb or something which is just for the OS or if I can use my current one (which already has the OS installed).fantomena If you mean just unplug the SSD from the current machine and put it into a new machine then I'd say sure, in my experience if it boots then windows will just use default drivers for the new hardware it finds. It might moan about the Serial Key but it should work. I wouldn't go swapping it back and forth between two PCs all the time but it should be fine to just swap over to a new build.
I simply plan to have one small SSD for OS, 2 1tb m.2 nvme SSDs for games and another regular external 2 TB HDD (in use now) for mostly games not really needing an SSD.