Windows 7 system requirements

If you want to run Windows 7 on your PC, here's what it takes:

• 1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor
• 1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
• 16 GB available hard disk space (32-bit) or 20 GB (64-bit)
• DirectX 9 graphics device with WDDM 1.0 or higher driver

Additional requirements to use certain features:

• Internet access (fees may apply)
• Depending on resolution, video playback may require additional memory and advanced graphics hardware
• Some games and programs might require a graphics card compatible with DirectX 10 or higher for optimal performance
• For some Windows Media Center functionality a TV tuner and additional hardware may be required
• Windows Touch and Tablet PCs require specific hardware
• HomeGroup requires a network and PCs running Windows 7
• DVD/CD authoring requires a compatible optical drive
• BitLocker requires Trusted Platform Module (TPM) 1.2
• BitLocker To Go requires a USB flash drive
• Windows XP Mode requires an additional 1 GB of RAM and an additional 15 GB of available hard disk space.
• Music and sound require audio output

Product functionality and graphics may vary based on your system configuration. Some features may require advanced or additional hardware.

PCs with multi-core processors:
Windows 7 was designed to work with today's multi-core processors. All 32-bit versions of Windows 7 can support up to 32 processor cores, while 64‑bit versions can support up to 256 processor cores.

PCs with multiple processors (CPUs):
Commercial servers, workstations, and other high-end PCs may have more than one physical processor. Windows 7 Professional, Enterprise, and Ultimate allow for two physical processors, providing the best performance on these computers. Windows 7 Starter, Home Basic, and Home Premium will recognize only one physical processor. 

source:http://windows.microsoft.com/en-us/windows7/products/system-requirements