Windows 8.1
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 (more info)
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