Revised March 22, 2014. After the publication of this report on September 5, 2013, Microsoft brought to the authors’ attention new information about its partnership with Chinese company 21Vianet. The original version of the report inaccurately characterized certain aspects of the Microsoft-21Vianet partnership. A revised discussion of this partnership is provided on pages 32-34. The authors would like to thank Microsoft for their assistance in clarifying the details of 21Vianet’s Windows Azure service.