The internal development codename for Windows 95 was Chicago.
Microsoft’s initial planning for the operating system began around March 1992, before Windows 3.1 had shipped. The company was pursuing two broad directions: Cairo, a high-end Windows NT project, and a consumer-focused evolution of Windows 3.1. That lower-end, compatibility-oriented project became code-named Chicago.
Chicago was intended to bring a 32-bit underlying kernel and file system, plus protected-mode device drivers, to mainstream personal computers. Microsoft also wanted it to support existing MS-DOS and 16-bit Windows software while adding preemptive multitasking and a friendlier graphical interface.
The code name remained visible during the preview period. Microsoft distributed technical and promotional material describing “Chicago” before the product received its retail name, Windows 95. The final operating system launched to manufacturing on July 14, 1995, and reached stores on August 24, 1995.
Nashville and Detroit were not the canonical codename for Windows 95. Memphis was associated with Windows 98, while Cairo was a separate NT-related project that never shipped as originally planned.