GATE

Hello,
Yes, if you want to get admission in IIT's or IISC, then you don't have to appear in GATE exam. You can also get admission through IIT JAM entrance test. Candidates who want to pursue post-graduation or dual degree courses from IITs and IISC, they have to clear an entrance exam.
IIT JAM is to take admission in M.Sc/Ph.D and other post graduate exams.
By qualifying JAM test, candidates can apply for:
1. M. Sc (2 years).
2. Joint M.Sc - Ph.D.
3. M.Sc. - Ph.D dual degree.
4. M.Sc - M.Tech.
5. Post bachelor degree courses at different IITs.
6. Integrated Ph.D courses at IISC.
You can check the below mentioned link to prepare for IIT JAM:
https://scoop.eduncle.com/iit-jam-exam-solved-question-papers-free-download
I hope it helps.

The Graduate Aptitude Test in Engineering (GATE) is an all-India examination that primarily tests the comprehensive understanding of various undergraduate subjects in engineering and science. Generally you will be appearing for GATE examination in your basic degree. For example, mechanical engineers appear for GATE in mechanical engineering.
The GATE examination consists of a single paper of 3-hour duration that contains 65 questions carrying a maximum of 100 marks. The question paper will consist of both multiple choice questions (MCQ) and numerical answer type (NAT) questions. The examination for all the papers is carried out in an online Computer Based Test (CBT) mode where the candidates will be shown the questions in a random sequence on a computer screen.