Microsoft's David Cole emailed Phil Barrett on September 30 1991: "It's pretty clear we need to make sure Windows 3.1 only runs on top of MS DOS or an OEM version of it," and "The approach we will take is to detect DR DOS 6 and refuse to load. The error message should be something like 'Invalid device driver interface."
MicroSoft wasn't exercising control over what you did with your Windows 3.1 there, they were just being a (anti-competitive) dick about what you ran it on. Having a controlled environment in this context is, controlling what can run in the environment that you provide, rather than controlling what environment the stuff you provide can run it.
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Microsoft's David Cole emailed Phil Barrett on September 30 1991: "It's pretty clear we need to make sure Windows 3.1 only runs on top of MS DOS or an OEM version of it," and "The approach we will take is to detect DR DOS 6 and refuse to load. The error message should be something like 'Invalid device driver interface."
MicroSoft wasn't exercising control over what you did with your Windows 3.1 there, they were just being a (anti-competitive) dick about what you ran it on. Having a controlled environment in this context is, controlling what can run in the environment that you provide, rather than controlling what environment the stuff you provide can run it.