There might be scattered articles about the differences among the many UNIX flavors, but at this point, there are 3 that are in major use. All are based on BSD. You might want see:
1. http://searchenterpriselinux.techtarget.com/answer/The-differences-between-System-V-and-BSD-Unix which requires a free login to see it.
2. https://kb.iu.edu/data/agjs.html for more historical info
You can also do a google search on "system V vs. bsd" spelled exactly like that (without the quotes) and see a few more references. The Wikipedia reference gives the names of the 3 major flavors.
