Earlier at least half of the IITs had interviews for M.Tech. Now most are having direct admits.
For actual cutoff range please see the respective tab at bottom: http://www.gatecse.in/cut-off-for-masters-admissions/
IISc. Offers direct admit for ME (same as M.Tech. elsewhere) in CSA, SSA, and DESE departments. CSA is Computer Science department, SSA is a joint one of CSA and EE depts and DESE is more on electronic side (embedded). Then there is M.Tech. in SERC which is the super computing department and works on many system side subjects. This has interview. Also, all these departments take interviews for MSc. (same as MS elsewhere).
IITB: M.Tech TA is the normal 2 year M.Tech. and is direct admit. There is also M.Tech. 3 years which has interview. This can be considered like MS elsewhere.
IITD, IITK: Offers direct admit for select few students (who have high CGPA and GATE score) and for others interview is there.
IITKgp, IITG, IITM, IITH: Direct admits for M.Tech. interviews for MS.
More information including interview experience you can get from http://lr.gatecse.in.
For interviews there might be a screening round where GATE level questions are asked. Sometimes it is more on aptitude side and last year some had plenty of geometry questions also. But areas deep into CN, CO etc. are usually not asked and maths, algorithm, operating system etc. are more important.
Now, for interviews your profile has a huge impact. I say about research interviews only as for M.Tech, it is usually for namesake.
- Say if you are a university topper (a university topper in PG has research admit granted due to INSPIRE scholarship) or with high CGPA, NTSE or similar scholarship winner, some other achievements etc. you have a clear advantage.
- Another criteria is research publication- if you have published a work somewhere, it shows that you have research interest- even if work is not great, and professors value it. So, if you are a final year student get your project published- it is not very difficult.
- Be smart in some areas. For GATE one need not be smart in any areas and just basic level knowledge is enough. But for demonstrating research interest one need to show real knowledge - mostly outside text book. This is easy for someone who work in a related area on company- say like those working in Intel and CO area, Cisco and Network area etc. Otherwise one can read the recent publications of the professors of the IITs you are going and get an idea of their work. Reading papers might not be easy but it would help.
- Selecting area of interest: This is quite tricky because unless experienced you can't really know your strength as GATE is a very basic level exam. In GATE you are studying like 15 subjects say at 5% depth and now you are going to take 1-2 among them and going to study at 50-80% depth. So, you shouldn't decide this based on your scoring in GATE or B.Tech. For example, in research in DBMS one mostly works on query optimization and not SQL queries as in B.Tech. In Compilers also one works on code optimizations and mostly not on parsing. Most people select algorithms and data structure- but these are mostly theoretical area and recommended only for those who want to be in academia. System side like OS, Compilers, CO etc can get you job in Intel, MS, Google, Nvidia etc. and Intelligence side like Machine Learning can get you jobs in ecommerce giants like Amazon as well as Google, MS, FB etc. Those who are good at GATE questions in CO, OS can safely take system side. Those who are good in probability can take Intelligence area.
If your profile is normal, I'm no way saying that you cannot be selected- many people do. My only point is that if you add something extra you do have a better chance. A good performance in interview gives selection most of the time.