After 30 Years, We Finally Know Why Windows 95's Installer Juggled Three Operating Systems

In a technical blog post, Microsoft veteran Raymond Chen has explained why Windows 95's installation process required users to pass through three different operating systems -- MS-DOS, Windows 3.1, and Windows 95. The design choice stemmed from the need to support upgrades from multiple starting points while maintaining a graphical user interface throughout the process. Rather than creating separate installers for MS-DOS, Windows 3.1, and Windows 95 users, developers opted for a unified approach using three chained setup programs. The process began with installing a minimal version of Windows 3.1 when starting from MS-DOS, followed by a 16-bit Windows application that handled core installation tasks, and concluded with a 32-bit Windows 95 program for final configuration steps.

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