If an innovation is perceived as difficult to use it will diffuse more slowly than one that is easy to understand. For example users of early personal computers needed an understanding of a programming language in order to use their machines. For most potential PC users this made the innovation too complex to consider buying. Then a graphical user interface was developed and incorporated by Apple Computer into the Lisa computer in 1983 (Figure 71) and more successfully into the Macintosh computer in 1984. Users could control their computer by using a mouse to point at visible icons on a virtual desktop and software became simpler to use. This approach was taken up by newly emerging PC manufacturers and the rate of diffusion of the personal computer increased. Of course, other factors contributed to the spread of the PC, such as falling cost, improved performance and more powerful software, but reduced complexity for users was a significant factor.