cublas64_50_35.dll and cudart64_50_35.dll ?

I created a new project and copied over some code from another project (all in W7 64 using VS 2010).

As far as I could tell I set all the project configurations the same, but when I ran some code which used cublas_v2 it ran 20% slower than it did in other project.

After some looking around I saw that the cublas64_50_35.dll and the cudart64_50_35.dll were not in the new project folder. So I copied and pasted and manually (through visual studio) included them in project.

Then the speed got back to that of the other project, but I am still unclear what happened and why?

What are the roles of these specific .dll(s) and how does one make sure they are being used? I am assuming it has to do with either the configuration of the VC++ directories or the linker (Additional Dependencies).