Windows 8 works great on the same hardware that powers Windows 7:
• 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:
• 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.
• To snap apps, you need a screen resolution of at least 1366 x 768.
From Windows 8 FAQ