In the new test build of Windows 11 24H2 Build 26058, Microsoft confirmed in the processor requirements the support of the PopCnt instruction (Population count — count number of bits set to 1, included in the SSE4.2 set for Intel or Advanced Bit Manipulation (ABM) for AMD). old CPUs do not have. When trying to boot Windows 11 24H2 on a PC with a CPU without PopCnt instruction support, the system does not startand hangs on the loading screen with the Windows logo.

AMD processors have supported the PopCnt instruction since 2006 after the release of the Barcelona architecture, Intel added PopCnt support in the Nehalem microarchitecture in 2008 (in the first generation of the Core i series). For example, AMD Turion II and Intel Core 2 Duo PCs do not have this instruction and will not be able to run the new version of Windows 11 on them unless a workaround is found for this limitation.

Until developers of third-party utilities to help with Windows 11 installation (such as Rufus) implemented a workaround for this limitation from Microsoft.

In fact, Windows 11 24H2 will run on a PC with an Intel Core 2 Quad Q9650, but the system will run on a Celeron J4005.

Profile experts added that while it is not clear why Microsoft has made support for this instruction mandatory, it may be required by some features of Windows 11 24H2, as the error description of the PC system requirements states that Microsoft considers the need to support the PopCnt instruction to be a critical feature.

Microsoft has previously struggled several times with workarounds to install Windows 11 on PCs without TPM 2.0 and modern CPUs. Microsoft insists that PCs with TPM and the new OS will help provide a higher level of protection against various attacks. Microsoft advises regular users to buy a new computer or laptop with Windows 11 instead of their outdated device.