Gate exam consists of 3 portion: Technical, Mathematical engineering, Aptitude.
Exam is divided in 3 slots.1st slot is for technicality examinations. 2nd and 3rd slots are common where you will have to choose one portion while another portion are compulsory.
This year exam is conducted by IIT Roorkee. It also published revised syllabus for exam. You can surely take help from this.
Syllabus is available on the site: ” http://gate.iitr.ernet.in/wp-content/uploads/2016/07/Syllabi_GATE2017.pdf ”
Have a look on syllabus.
All the best.