What is the best method of reducing lag when recording?

I have repeatedly tried to record PC gameplay but I keep on getting lag not only on the videos but on the games I play too. I have tried using different recorders like Camtasia Recorder, Dxtory and Bandicam but the results do not change that much. I am running Windows 8.1 on my Pc and it has a 4 GB RAM, AMD A8 CPU, Generic PnP graphics (1600×900@60Hz) and 698 GB in storage space left. What could be the issue? How can I solve it?
