Microsoft began testing Windows 11 builds that require POPCNT CPU instructions for certain system functionality back in February. The newer Windows 11 Build 26080 will not run on processors that do not support the POPCNT instruction set. Instead, the computer will get stuck in a reboot loop. Microsoft did not make an official comment on this change when asked by The Register.

The POPCNT CPU instruction set is part of the SSE4.2 instruction set. Intel introduced these instructions with the first generations of Core i5 and Core i7 processors, while AMD did it with the Bulldozer generation. Unfortunately, there is no workaround for missing CPU instructions.

The official system requirements for Microsoft Windows 11 include eighth generation Intel Core processors and higher, second generation Ryzen processors and higher, and other CPU models with TPM 2.0 support. The new change only affects users who bypassed these requirements on older computers. Users with computers that do not meet these requirements can still use Windows 10, but support for this version of the operating system ends in 2025, unless they pay for additional support, the price of which is not yet known.

Users with older processors will have to go back to Windows 10 or consider using other operating systems, such as Linux distributions. However, some apps and games may not work without the mentioned CPU instructions, such as the popular game Apex Legends. A new version of the Windows operating system may appear as Windows 12 and could have even more demanding system specifications than Windows 11. However, all processors that do not support POPCNT instructions are already officially unsupported, which means that many computers with such hardware will probably still they use older versions of the Windows operating system.