To run Win8, the processor must support PAE/NX/SSE2

What are PAE, NX and SSE2, and why does my computer need to support them in order to run Windows 8? Let's take a look at the detailed description of Microsoft's official website:
Physical Address Extension (PAE), NX Processor Bit (NX), and Streaming Single Instruction Multiple Data Extensions Instruction Set 2 (SSE2) represent the capabilities of the processor.
PAE Support 32-bit processors can access Windows with more than 4 GB of physical memory functional version, and it is a prerequisite for NX. NX allows the processor to help protect your computer from malware. SSE2, a long-standing standard for processors, is a set of instructions used by more and more third-party applications and drivers.

For Windows 8, for malware defenses to work, we require your processor to support NX. To enhance the reliability of third-party applications and drivers running in Windows 8, SSE2 is also required.
If your computer does not support PAE, NX and SSE2, you will not be able to install Windows 8. If your processor does not support PAE and SSE2, the Upgrade Assistant will provide you with an error message. If the processor does not support NX or the NX in the computer BiOS is turned off, you will also see a notification. Windows 8 installation will attempt to enable NX during installation, and if NX is not enabled, your computer will be restored to the current operating system.