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 !!Microsoft Business Practices 

  

 Windows 3.1 gave a warning message if it was being run on DRDOS rather than MSDOS, even though it worked just as well on either. Presumably this was to scare people into only using MSDOS. 

  

 In the early nineties, a company named "Stac" had as its flagship product a program named "Stacker", that transparently compressed and then de-compressed files on-the-fly. This product had versions for MS-DOS version 5, [IBM]'s OS/2, and [Apple]'s [Macintosh] operating systems. Microsoft 

 were interested in incorporating this functionality in their next version, MS-DOS 6, and approached Stac about licensing. During discussions, Microsoft gained information about technical details of the software. When MS-DOS 6 came out, it included !DoubleSpace, which eventually a jury found infringed on Stac's patents, and Stac was awarded US$120 million damages. But by then it didn't matter, as their product was effectively marginalised. (Incidentally, Microsoft counter-claimed that Stac had illegally reversed engineered MS-DOS because they were using undocumented DOS functions). Also, MSDOS 6.0 included changes that broke Stacker, although the company quickly produced an updated version that worked with 6.0.