The three desktop editions of Windows 8 support 32-bit and 64-bit architectures; retail copies of Windows 8 include install DVDs for both architectures, while the online installer automatically installs the version corresponding with the architecture of the system's existing Windows installation. The 32-bit version runs on CPUs compatible with x86 architecture 3rd generation (known as IA-32) or newer, and can run 32-bit and 16-bit applications, although 16-bit support must be enabled first. (16-bit applications are developed for CPUs compatible with x86 2nd generation, first conceived in 1978. Microsoft started moving away from this architecture after Windows 95.)
Is there an answer to this question (If it cannot be answered, say "unanswerable"): How does the online Windows installer know which version to uninstall?
unanswerable