Microsoft is now officially blocking the installation of Windows 7 and 8.1 updates on systems with Intel 7th Generation Core (a.k.a. Kaby Lake) and AMD Ryzen processors: If your system has an Intel 6th Generation Core processor (a.k.a. Skylake), then only some of them will continue to be supported in Windows 7 and 8.1. 16 OEMs will support 7 and 8.1 on certain Skylake model machines. You can read the full details on this Ars Technica article.