This behavior has been changed in Windows 8 Release Preview. Instead, users are blocked from installing if the processor (CPU) doesn’t support PAE, and receive the error:
Your PC’s CPU isn’t compatible with Windows 8
Setup then rolls back to Windows 7.
Whenever I try to install Windows 8 Consumer Preview, I get the following error:
Windows failed to start. A recent hardware or software change might be the cause. To fix the problem:
1. Insert your windows installation disc and restart your computer.
2. Choose your language settings, and then click "Next".
3. Click "Repair your computer."
If you do not have this disc, contact your system administrator or computer manufacturer for assistance.
Info: An unexpected error has occurred.
Before Windows 7 is reset, the Windows 8 Setup shows:
“We couldn’t install Windows 8 Consumer Preview. We’re not sure what happened, but we couldn’t finish installing Windows 8 Consumer Preview. We’ve set your PC back to the way it was.”