Recommended:

OS: Windows Vista SP2 or Windows 7 SP1 or Windows 8 (both 32/64bit versions)
Processor: Intel Core i5 2400S @ 2.5 GHz or better or AMD Phenom II x4 940 @ 3.0 GHz
Memory: 4 GB RAM
Graphics: Nvidia GeForce GTX 470 or AMD Radeon HD 5850 (1024MB VRAM with Shader Model 5.0) or better
Storage: 30 GB available space
Sound Card: DirectX Compatible Sound Card with latest drivers
Additional Notes: Supported video cards at the time of release: Nvidia GeForce GTX 260 or better and GeForce GTX 400, GTX 500, GTX 600 and GTX 700 series. AMD Radeon HD4870 or better and Radeon HD5000, HD6000 and HD7000 series. Note: Latest GeForce drivers tested: 327.23 for all series. Latest Radeon drivers tested: 13.1 for Radeon HD4000, 13.4 for Radeon HD5000, HD6000 and HD7000 series on Vista and 13.9 for Radeon HD5000, HD6000 and HD7000 series on Win7 and Win8. Laptop versions of these cards may work but are NOT officially supported.

Assassin's creed