Treshim gonna be majoring in comp sci so im pretty sure im gonna need windows (not sure on this one)
my budgets like around 800, but im okay with spending a little more if its good
OS might be dependent on what exactly your department does but in my case i use eclipse which is on every OS. i have it on my mac and the pcs for in class labs are running some linux version (i think it's ubuntu or something similar). Look at what your specific university recommends for computers.
Also look if they have a student laptop program. Some (most?) universities partner with laptop companies to get you a discount if you buy the laptop through your universities bookstore. For example I could buy a macbook air with applecare for $210 cheaper. They probably won't have a great variety but it's a good way to save some money if one of them looks good for you. Plus, at least in my case you get tech support through the university and if it breaks they have a loaner pool while yours gets repaired. Still always be sure to price shop, it could always be cheaper somewhere else.