We already know that Watch Dogs has some rather lofty system requirements for the PC version of the game. Earlier today, Jonathan Morin, the Creative Director for Watch Dogs, shared some more specific details on how the game will run on less than optimal hardware.
According to Morin, dual-cores CPUs will not be able to run Watch_Dogs (so it will be interesting to see how our simulated dual-core system will behave).

Not only that, but the game may not even boot if PC gamers are not equipped with 6GB of RAM. When a fan asked Morin whether the game would run on his PC system that was equipped with 4GB of RAM, Morin replied and said that he should climb it up to 6GB.

Alright, so you will need at least 6GB of memory. What else?

Here are the CPU's listed based on Intel's PassMark test. To have at least 9,000 on that scale, it looks like you will need at least a higher end i7 and above.