Computer Science-Gate for Electronics Communication student.

Hi guys, I would be obtaining BE. in EXTC in this year.
Right from the time I have began to program, I started to develop a liking for computer science.
Hence I decided to get my major in CS.

However I lack the formal background of Discrete Maths, Theory of Computation, Operating Systems, Computer Architecture.
I can manage things little bit with Datastructures and Algorithms as I have self studied them for some time now.

I want to appear for GATE-CS 2013 and so I think I have time in my hands to get my basics correctly done.

Thus I want to know in which order should I proceed, which subjects first.