The more people buy iPhones and iPads, the more software developers and media companies want to write applications for them, as various as games and digital magazines. And consumers are more likely to buy iPhones and iPads when more entertainment and information applications are available on them. The combination of hardware, software and services is what corporate executives, economists and analysts call a platform. Successful technology platforms sustain and reinforce growth. And this self-reinforcing cycle is known as a network effect. It helps the platform owner and raises a barrier to competitors.