What was the code name for Windows 95 during development?

The code name for Windows 95 during development was Chicago. Microsoft began developing the consumer-focused operating system around March 1992, shortly after Windows 3.1, with Chicago intended to modernize the Windows experience while preserving compatibility with existing MS-DOS and Windows software.

Chicago was planned as a major transition toward 32-bit computing. Microsoft incorporated the Win32 programming interface and worked toward features such as preemptive multitasking, Plug and Play hardware support, and a redesigned user experience. Some 16-bit components remained because backward compatibility was extremely important to users and software makers of the period.

Microsoft eventually replaced the development name with Windows 95, linking the product to its planned release year. The operating system was released to manufacturing on July 14, 1995, and reached retail stores on August 24, 1995. Other names in the options are associated with different Microsoft projects: Longhorn was an early codename for Windows Vista, while Neptune referred to a planned Windows release that was ultimately canceled.