Second System for Windows 8.1 is now here! Run many modern applications including the latest Firefox, Google Chrome and Steam clients, productivity applications like Kdenlive and more! And limited AVX emulation for when your older system needs an extra push.
Our work is far from done, however. Compatibility with Windows 10, 32 bit versions of Windows, D3D12, modern network cards, modern toast notifications and more is still on the way.
Some Installation Notes:
Windows 8.1 requires that some system DLL substitutes be present in the system32/syswow64 folders. For this reason, administrator privileges are required to install this version of Second System. Elevation will be prompted automatically upon running InstallSecondSystem.cmd.
Revised 2025-10-16 (1323 UTC-4, but only noted here at 1517 UTC-4 due to an omission) to change the 32-64 process hook and fix an issue in the wrapper for cfgmgr32.dll.
Revised 2025-10-25 (0308 UTC-4) to include subsystem version patching support for higher (2020+) update levels, definitions for several API set DLLs, fixes for Office 2019 applications and some reliability improvements regarding export forwards (primarily impacting version.dll):