I am not an IIT graduate and I presume that most likely it will be like the other engineering colleges only. It mainly differs from the position offered in the company coming for recruitment.
For my college all the Core(MECH,EE,CIVIL) followed the same pattern of recruitment with little changes in them. it goes like written test (APTI+TECH+BASIC ENGLISH) -> GD -> EXTEMPORE -> TECHNICAL INTERVIEW(Includes case study cracking technically) -> HR INTERVIEW.
I have attended drive for a software company which is a service based it concentrated mainly on quick wits and fluency in English. Although they had a similar process, the start was with not written exam its with a telephonic interview in the campus only.
thats it !!