From the System Requirements for Windows 10 Preivew:
"Basically, if your PC can run Windows 8.1, you’re good to go."
From the Windows 8(.1) system requirements:
If you want to run Windows 8.1 on your PC, here's what it takes:
- Processor: 1 gigahertz (GHz) or faster with support for PAE, NX, and SSE2
- RAM: 1 gigabyte (GB) (32-bit) or 2 GB (64-bit)
- Hard disk space: 16 GB (32-bit) or 20 GB (64-bit)
- Graphics card: Microsoft DirectX 9 graphics device with WDDM driver
So just like Windows 8.1, you'll need those CPU features to be able to run Windows 10.