Windows 8.1  works great on the same hardware that powers Windows 8:

Processor: 1 gigahertz (GHz) or faster
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

Additional requirements to use certain features:

For 64-bit installations of Windows 8.1 , your CPU must also support CompareExchange16b, PrefetchW and LAHF/SAHF.
To use touch, you need a tablet or a monitor that supports multitouch.
To access the Windows Store and to download and run apps, you need an active Internet connection and a screen resolution of at least 1024 x 768, and a Microsoft account.
To snap apps, you need a screen resolution of at least 1366 x 768.
Internet access (ISP fees might apply)
Some features such as touch and Client Hyper-V may require advanced or Windows 8 certified hardware

The Windows To Go feature requires advanced hardware. To learn more about USB drives certified for Windows To Go, please visit www.microsoft.com/WindowsToGo.