If you find all of that too hard / complicated / annoying to do
A sure fire way to find out is, reboot computer, go into bios, and it should display it there as a code, the code has the SPECIFIC hard drive you have, IF you have trouble understanding the code, just copy it and then google it, 100% the correct drive and you dont have to worry what OS you've got, (cus not everyone uses windows, not to mention the huge number of windows OS out there)
EDIT: to enter BIOS, after you restart computer, when its loading in that black ish screen, keep tapping Delete, or F8