Check otu the updated Civilization 5 PC System Requirements from developer Firaxis:
Civilization 5 PC System Minimum Requirements
Operating System: Windows? XP SP3/ Windows Vista SP2/ Windows 7
Processor: Dual Core CPU
Memory: 2GB RAM
Hard Disk Space: 8 GB Free
DVD-ROM Drive: Required for disc-based installation
Video: 256 MB ATI HD2600 XT or better, 256 MB nVidia 7900 GS or better, or Core i3 or better integrated graphics
Sound: DirectX 9.0c-compatible sound card
DirectX: DirectX version 9.0c
Civilization 5 PC Recommended System Requirements after the jump.
Civ 5 Recommended Specs
Operating System: Windows Vista SP2/ Windows 7
Processor: 1.8 GHz Quad Core CPU
Memory: 4 GB RAM
Hard Disk Space: 8 GB Free
DVD-ROM Drive: Required for disc-based installation
Video: 512 MB ATI 4800 series or better, 512 MB nVidia 9800 series or better
Sound: DirectX 9.0c-compatible sound card
DirectX: DirectX? version 11
