 As released, Windows NT 3.x went through three versions (3.1, 3.5, and 3.51), changes were primarily internal and reflected back end changes.The 3.5 release added support for new types of hardware and improved performance and data reliability; the 3.51 release was primarily to update the Win32 APIs to be compatible with software being written for the Win32c APIs in what became Windows 95.After Windows 3.11, Microsoft began to develop a new consumer oriented version of the operating system codenamed Chicago.