Simplify the following text for a Grade 4 native English-speaking person.
Original: As of October 2009 , Windows had approximately 91 % of the market share of the client operating systems for usage on the Internet . The most recent client version of Windows is Windows 7 ; the most recent server version is Windows Server 2008 R2 ; the most recent mobile OS version is Windows Phone 7 .
Simplified: The most recent change is Windows 7 which was made in 2009 .