Because folk got tired of 5 to 10 minute boot times the SSD is your boot drive and for mass storage that's on the large HDD.
225GB is plenty for the OS and what apps won't store on drive C.
I'd move your files to the second HDD and install your apps and enjoy the fast new PC.
I got a new Dell with a 225 ssd (c drive) and a 2Tb storage hd (d drive). I have an older HP with a 1 Tb hd with about 575 gigs on it. I can't transfer all my 575 gigs to the new 225 ssd (too small). I want to make my 2 Tb my C drive and make my 225 ssd into my "d" drive. That way I can zinstall all my existing 575 gigs to my new computer. How do I change drive letters making my D drive my C, and my C drive my D. I want to put my OS on my larger 2Tb hd. Can I just copy all the stuff on my small ssd to my large hd and change the drive letters so my 2Tb becomes my C drive with my OS (windows 10) on it and make my smaller 225 ssd my "d" drive with my recovery info on it? I think it was pretty lame for Dell to make my OS on such a small ssd drive. Any suggestions? Please? Thx.