I connected Sudderth with a top-level Microsoft support agent. Together, they determined that the issue was Sudderth's Intel DP35DP motherboard -- an older model that hasn't received a firmware update since 2009. While the Core 2 chips supported CMPXCHG16b, the motherboard itself did not. No Windows 8.1 for him -- or for this other Windows 8 user with an Intel DP35DP.
Unhappy Windows 8 users with an uncertain future
When asked to comment about compatibility issues, Microsoft representatives said technical support questions should go Microsoft's Answer Desk. However, Microsoft told Neowin that "the number of affected processors are extremely small, since this instruction has been supported for greater than 10 years."
As the troubles with Sudderth's shows, however, just because an instruction was supported 10 years ago doesn't mean it was ubiquitous 10 years ago. The Intel DP35DP was released six years ago, and the Core 2 family of processors was extremely popular.
"It's frustrating that an older but robust machine -- one that can play modern PC games and run Windows 8 flawlessly -- can be left behind after what is essentially a service pack release," Sudderth says. Other forum-goers echo the same irritation. "I hope that I'm a rare exception, but I'm also concerned that Windows developers will target Windows 8.1 and leave me behind just as Microsoft did."
The newly released modern UI Facebook app, for example, only runs in Windows 8.1.
More worrying than that, however, is Microsoft's plan to discontinue support for Windows 8 "vanilla" after 2015. Beyond then, you'll need Windows 8.1 installed to receive security patches and other updates.
What can you do if you're affected?
If you're stranded on Windows 8 and don't want to buy a new machine -- and why would you if it still rocks Battlefield without skipping a beat? -- all might not be lost.