What is U/WIN and what does it do? Solution U/Win is a software package. It is used to run Unix applications in windows. For eample if u have some programs which were written for the UNIX environment, you can use U/WIN to run those programs in windows systems by making few or no changes. U/WIN contains libraries that emulate UNIX environment by implementing the UNIX API. Most of the Unix API is implemented by the POSIX.DLL dynamically loaded library (DLL). Programs linked with POSIX.DLL run under the Win32 subsystem instead of the POSIX subsystem. so programs can freely intermix Unix and Win32 library calls..