The initial design and planning of Windows 95 can be traced back to around March 1992, just after the release of Windows 3.1. At this time, Windows for Workgroups 3.1 and Windows NT 3.1 were still in development and Microsoft's plan for the future was focused on Cairo. Cairo would be Microsoft's next-generation operating system based on Windows NT and featuring a new user interface and an object-based file system, but it was not planned to be shipped before 1994 (Cairo would eventually partially ship in July 1996 in the form of Windows NT 4.0, but without the object-based file system, which would later evolve into WinFS).