Enlarge / We've installed Windows 11 on systems as old as this Core 2 Duo Inspiron tower. As of version 24H2, the OS may no longer be bootable on these systems. (credit: Andrew Cunningham)
Officially, Windows 11 has higher system requirements than Windows 10. But to date, once you've bypassed those requirement checks, there have been few consequences to running Windows 11 on old hardware. Unsupported or not, Windows 11 would run on pretty much any 64-bit PC that could boot Windows 10—we've run it on PCs as old as a Windows XP-era Core 2 Duo desktop.
That's apparently changing a bit in Windows 11's 24H2 update, which Microsoft began testing earlier this month. According to posts from a user named Bob Pony on X, formerly Twitter, the latest Windows 11 builds refuse to boot on older processors that don't support a relatively obscure instruction called "POPCNT." Short for "population count," it's used for "counting the number of bits in a machine word," according to an explainer by programmer Vaibhav Sagar.
It's unclear why POPCNT has become the load-bearing CPU instruction for a whole bunch of Windows components, but it looks like the Windows kernel, the system's USB and network drivers, and other core system files now require the instruction as of Windows 11 24H2.
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