There are two types of high definition wallpaper – HD and 4K. Among them, 4K is the latest. It has a resolution of 3840×2160. It is the best option for mobile devices and desktops alike. The main difference between the two is the resolution. In other words, HD is the highest quality; whereas, a four-inch 4K screen is too small for mobile devices. However, if you are on a budget, a 4K wallpaper may be all you need.