Microsoft hosts the Windows source in a 300GB Git repository

Just as Windows' development had become complex and fragmented, so too did the company's internal systems for things like source control, issue tracking, testing, building, code analysis, and all the other tasks that fall under the application lifecycle management umbrella. And just as Windows' development was unified as OneCore, the company has embarked on an effort to unify its ALM and develop what it calls One Engineering System (1ES).The cornerstone of 1ES is TFS, but for 1ES, the company wanted to do more than just standardize on TFS; it wanted to switch to a single version control system. TFVC, Source Depot, and Git were the obvious contenders, though other options such as Mercurial were also considered. In the end, the company standardized on Git.Why reinvent the wheel all the time, when you can just use a tool everybody else is already using anyway?