In 2004, Microsoft reached a high with Windows PCs sold outnumbering Mac PCs by 56 times. However, that has ratio has now fallen to below 20, a level that was last reached before Windows 95 launched. If we taken into account iOS devices the multiple drops to below 2 with parity expected within a year or two.
The consequences are dire for Microsoft. The wiping out of any platform advantage around Windows will render it vulnerable to direct competition. This is not something it had to worry about before. Windows will have to compete not only for users, but for developer talent, investment by enterprises and the implicit goodwill it has had for more than a decade.
Take a look at the chart below to see this visualized.