Older computers that do not meet the new Windows 11 requirement, POPCNT, stopped working after updating to version 26080.
The official system requirements for Windows 11 are much higher than Windows 10, but there are solutions for installation of the operating system on older computers, which bypass these requirements.
But some old computers running Windows 11 after the their recent update to version 26080, which is currently available to Insiders, have now stopped working due to new guidelines for their CPU.
Microsoft started testing it in February 2024 requirement that the computer's CPU has the POPCNT command. It wasn't clear at the time if the change was intentional or accidental, but the newer Windows 11 Build 26080 won't even boot if your processor doesn't support POPCNT.
If you have already installed Windows 11 on an old computer that does not have POPCNT and you update Windows to canary version 26080, when booting they will get stuck in an endless reboot loop!.
The CPU POPCNT instruction is part of the SSE4.2 instruction set. Intel added it with the first generation of Core i5 and Core i7 processors (Nehalem architecture) in 2008. AMD added the SSE4.2 instruction set to its Bulldozer processors in 2013. The POPCNT instruction was supported on earlier AMD CPUs, but only with the incomplete SSE4a instruction set, which Windows 11 does not appear to support. There is no workaround for the lack of CPU instructions.
Microsoft's official system requirements for Windows 11 already included an eighth-generation Intel Core processor or later, or a second-generation Ryzen processor or later, as well as other PC features such as TPM 2.0.
The latest update only affects people who bypassed these official requirements on computers with old processors.
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