On my laptop I have W7 installed on sda2 (sda1 is a 100 MB partition that W7 makes by default). I installed arch and did
grub-mkconfig -o /boot/grub/grub.cfg grub-install /dev/sda
I didn't think about W7, it's my firs time actually installing Arch outside a VM. I read that you should install grub on sda1 to be able to dualboot Windows and Arch. So my question is, is there anyway I can dualboot the two without having to reinstall Arch?