Scaling
Integer scaling
Integer scaling is scaling by a factor of a whole number, so 2x, 3x, 4x, etc. In RetroArch, the option scales the image up to the greatest integer scale below the set resolution. So for instance, if you set your fullscreen resolution to 1920x1080 and enable integer scaling, it will only scale a 320x240 image up to 1280x960, and leave black borders all around.