As incredible as it may seem, Windows 7 still offered support for pre-2000 processors until recently, when Microsoft confirmed that machines without SSE2 support must be upgraded to continue receiving updates for the operating system. Back in March, the company mentioned that a workaround for non-SSE2 processors was under development.
https://www.notebookcheck.net/Microsoft-drops-Windows-7-support-for-Pentium-III-processors.310654.0.html