Microsoft's switch to using Git as the version control system for Windows' development has resulted in many challenges. Git wasn't really built for a 300GB repository with 3.5 million files, and the engineering effort to make Git scale in this way continues.
But in adopting and developing what the company is calling One Engineering System (1ES), the Windows and Devices Group (WDG) has adopted more than just Git; the group has also adopted Visual Studio Team Services (VSTS), the company's source control, item tracking, integration and testing system, and with VSTS a more integrated, devops style approach to developing. Git is an important part of this but far from the whole story. Microsoft wrote today about some of its experiences using VSTS, including some of the problems the scale of the operation has caused.
The adoption of VSTS features and devops practices isn't uniform across WDG. Continuous integration and continuous delivery make sense for some parts of WDG—online services are an obvious example, and even some of the apps in the Microsoft Store could qualify—but they're less applicable to the core Windows operating system itself. Nonetheless, the company has worked to standardize practices that are common to every component.