Some users using Windows 8 CP reported on the Microsoft Answers forum that they’re getting a warning message from Upgrade Assistant when they try to run Windows 8 RP setup (online installer) on their Computers. Here is the message shown on the Windows 8 Setup window: “This PC doesn’t meet system requirements. If you want to install Windows 8, you may have to upgrade some of the hardware in this Computer.Your PC’s CPU isn’t Compatible with Windows 8”.

Where the problem lies? Why the CPU that worked in Consumer Preview totally gone incompatible with Windows 8 RP?

First check your system meets Windows 8 System requirements, to run Windows 8, your system’s Processor speed should be 1GHz or more. According to Steven.s, forum moderator in issue reported thread “ to install Windows 8 Release Preview on your PC, the processor (CPU) must support the following features: Physical Address Extension (PAE), NX, and SSE2.”  Where NX stands for “No Execute Bit”.

your PC's cpu not Windows 8 compatible

Most CPUs coming these days supports the above said features. “Windows 8 requires the NX capabilities of modern CPUs. This is done for security reasons to ensure that malware defense features work reliably. This is important as we want to ensure that people can feel safe using lots of different software including desktop apps and apps from the Windows Store. This means some very old CPUs will not work with Windows 8. In the CP we did not block the installer for the NX feature” said Bill fill of Microsoft.

Based on CP telemetry, for Release Preview, Microsoft made NX capabilities for CPUs as a must. That’s why you’re getting that error message as Windows 8 RP’s web installer set to block for NX features.

Workaround for the error

Enable NX in BIOS Security settings: Your CPU might support NX, but it might not had been enabled in the BIOS settings. You need to look for “No execute bit” or equivalent XD (“Execute Disable bit”) in security settings and enable the same, save the changes and restart your PC.

After making the above changes, when you run Windows 8 RP installation by booting from a DVD/USB drive, RP will be successfully installed. If you get a code 5D  blue screen error, that means, then your CPU doesn’t support NX capabilities.

P.S : I’ve not experienced this error, I produced the above screenshot by disabling “ Execute Disable bit” in BIOS Security settings and ran Windows 8 RP setup after that. I’ve done that to capture the screenshot, don’t play with the BIOS settings.