A person with a valid GATE score more than 700 get call for interview and rank under 2k in most of the IITs in CS candidates can apply to some other departments too, but that depends on the course being offered by the institute and the individuals interest.

Sometimes rank below this are also get call for interview in new ones but several factors such as the cutoff ranks for different institutes, the number of seats available, and the competition in the particular year changes cutoff every year.