page_title: Windows Neptune
hierarchical_section_title: Windows Neptune
caption_attribution_description: English: Windows Neptune showing the login screen.
context_page_description: Neptune was the codename for a version of Microsoft Windows under development in 1999. Based on Windows 2000, it was to replace the Windows 9x series and was scheduled to be the first consumer version of Windows built on Windows NT code.
context_section_description: Neptune  was the codename for a version of Microsoft Windows under development in 1999. Based on Windows 2000, it was to replace the Windows 9x series and was scheduled to be the first consumer version of Windows built on Windows NT code.
caption: Neptune build 5111 logon screen
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