boot = {
    loader.grub = {
      memtest86.enable = true;
      version = 2;
      enable = true;
      device = "/dev/sda";
      extraEntries = ''
        menuentry "Windows 7" {
          insmod part_gpt
          insmod chain
          set root="hd1,msdos1"
          chainloader +1
        }
      '';
    };