[A2A] There may be some mistakes in my answer. Please feel free to correct me. IIT-JEE in the 1990’s consisted of three subjective paper, one for each subject. Then, sometime in the late 90’s, they introduced an objective section in the same three papers, so that they would first only correct the objective section and then shortlist people based on the results of the objective section and then correct the subjective part of the shortlisted people.
In 2000, they introduced a screening exam in JEE called JEE Screening, where there would be a single objective exam of three hours containing all three subjects and then based on that they would shortlist around 20,000 candidates for JEE Mains. JEE Mains consisted of three subjective exam for each of the three subjects of two hours each. Then, the final JEE rank was decided solely on the marks of JEE Mains exam. This is the pattern on which I gave my JEE in 2003.
I don’t know how the pattern has evolved from then on. One observation on the recent system: I don’t how they came up with nomenclature, JEE Mains and JEE Advanced. It seems a little funny to me that the main JEE exam is not called JEE Mains, but JEE Advanced.
But, I feel that the quality of questions on the JEE paper saw a considerable dip from 1990s to 2003 when I gave the exam. It was much easier in my time. I guess they did this to reduce the influence of coachings, but unfortunately, coachings were on a rise then and are on an even bigger rise now.