Assassin's Creed Unity PC requires 6GB of RAM, GTX 680
 

Ubisoft has posted the hardware requirements for the PC version of Assassin's Creed Unity, and they're a doozy. In addition to 50GB of free storage space and a 64-bit version of Windows 7 SP1 or later, the minimum requirements call for:

Yep, that's six gigs of RAM and a high-end Kepler GPU at minimum . ...

http://techreport.com/news/27261/***...of-ram-gtx-680