Your PC's CPU isn't compatible with Windows 8: Windows 8 Release Preview installation error
Did you try to install Windows 8 Release Preview and got stuck with the error - Your PC's CPU isn't compatible with Windows 8? Learn the causes of this Windows 8 RP installation error and the solution to this problem.
Windows 8 Release Preview was just announced by Microsoft and a lot of active Windows users have already started using it. If you have not installed Windows 8 RP yet, try to download Windows 8 Release Preview from Microsoft Windows 8 website.
Some people have reported an error "Your PC's CPU isn't compatible with Windows 8" while trying to install Windows 8 RP.
Error details
When running the Windows 8 upgrade assistant, the following error is displayed:
Your PC's CPU isn't compatible with Windows 8
If you want to install Windows 8, you may have to upgrade some of the hardware in this computer.
Your PC's CPU is not compatible with Windows 8
This error happens when upgrading to Windows 8 RP on some old computers which has a non compatible CPU. Even though Windows 8 Release Preview System Requirements does not mention anything specifically about these, it has been clarified that your CPU must support the following features:
If you like to install Windows 8 Release Preview on your computer, make sure your CPU supports the following features:
Most of the new CPUs have these features enabled by default. If you receive the error "Your PC's CPU isn't compatible with Windows 8", that indicates you may not have these features enabled or supported in your CPU.
Another potential reason for the Windows 8 release preview installation error while using virtualization software is, you may not have PAE or PAE-NX enabled. Check out the configuration settings for your virtualization software to find the PAE option and enable it before you proceed with Windows 8 RP installation.Solution for the error "Your PC's CPU isn't compatible with Windows 8"
Most people have reported that the error went away when they enabled XD in their BIOS setup. If you haven't tried enabling XD in your BIOS, try it now and see if it resolve your Windows 8 RP installation error.
To enable NX bit flag, follow the steps below:
1. Restart your computer
2. Press the system key to open BIOS
3. Go to security tab
4. Enable the NX/XD bit flag to ON
5. Save BIOS settings and start computer.
Learn more on how to enable NX or XD in BIOS for Windows 8Workaround for "Your PC's CPU isn't compatible with Windows 8" error
If you are unable to find and enable the NX bit, then you may try this work around suggested by Microsoft. This work around will work in most cases but could fail with a blue screen in case of old CPUs that has no NX capability at all.
After downloading the .ISO image for Windows 8 RP, make a bootable DVD or bootable flash drive. Then boot from the bootable device and start the installation from the media.
Microsoft suggests this work around may work out because when you boot from the media, the is installer uses a different setup program found in the root of the bootable media. This setup program used by the bootable media does not do the NX check on the CPU, instead, it tries to activate the NX bit by itself, provided your CPU supports the NX bit.
How to enable NX or XD feature for your CPU
If you get the Windows 8 Release Preview installation error and suspect that you do not have the NX feature enabled, go to your BIOS settings. To go to the BIOS settings, you will need to reboot your system and press some special keys while booting. The key to get the BIOS setup is different for each computer and is set by the manufacturer. Refer to your documentation to figure out how to get to the BIOS.
Look for the NX option in your BIOS setup under the security settings. If it is currently disabled, Enable it and start the computer. Try to install Windows 8 Release Preview again. Hopefully, you will not get the error Your PC's CPU isn't compatible with Windows 8 anymore.
If you cannot locate the NX settings in your BIOS, that may indicate you do not have that option and probably you have a very old BIOS version. In that case, you will need to contact the manufacturer to get the updated version of BIOS program to get NX setup option. Some old CPUs may not even support that option and that would make it incompatible with Windows 8 release preview.
Follow 
HI Good article but on my PC W8 Consumer preview is working fine bot W8 RP is showing this message.. Any Idea Why?...
My CPU is E2140 & all required bits are enabled in bios...