Hi everyone, I'm Debanjan Das. I got air 1196 (score 676, category:General) in Gate CS 2024. I got shortlisted to appear for the IIT Madras MS written test, interview offered by the Computer Science Department.
The following is the detailed description of my written exam as well as interview experience for Theoritical Computer Science and Computer Systems panel.
Shortlisting Criteria:-
Received mail on 17/4/24, intimating abt the test and the panels available.Total 235 students were shorlisted for the exam.
Panels:-
Test Experience(6th May):-
First the candidates were asked to sit in the Aryabhatta hall where the Head of the Department, Prof K Nandivada gave a presentation about the MS,PhD program, ( https://drive.google.com/drive/folders/1Qsg2372njMMdYIzyKPB3pNnwOrGX6-it?usp=drive_link ), the Test was conducted in the IIT Madras Labs(mine was in LAB 1 DCF main), on the IITM-Moodle platform on 6th may from 10:00-12:00.
Paper pattern:-
There were 30 questions(+2,-0.5), out of which we are supposed to answer any 20 questions, the lab TAs and the concerned professor ( Proff KM Sivalingam)told evaluation will be done on all the questions a student attempt, if someone attempts extra questions and make mistakes , then the negatives will be counted in the total marks obtained(i.e if someone attempts 25 q and make 20 crct then also negative marks of those 5 wrongly attempted questions will impact the total marks).
Questions:-
https://docs.google.com/document/d/1AMzr4uHe5V44Al1g6yPHlNg60VZ5kCauWtPFdFx9k6E/edit?usp=sharing
credits @Psy Duck's interview experience ( https://gateoverflow.in/blog/15846/iit-madras-ms-2024-interview-experience)
On 13:30 the shorlist was out, 44 students were shortlisted for the interviews ( https://drive.google.com/file/d/1NIK2w1cI-l_SPhgqcEMd5WVAijXFwiMK/view?usp=drive_link ), I made it to the interviews!!
This was followed by filling a form(name, college sem wise marks,panels to chose etc), document verification.Then it was announced that PhD and MS panel B,A interviews will be conducted that day only. Originally my aim was to only appear for panel B(systems), but needed some time to prepare so to avoid the panel B interview, I also selected panel A and went to appear for panel A interview(this was the first interview of my life! and i kinda messed up though)
Panel A(Theoritical computer science) interview experience(6th May ~17:00 hrs):-
Professors in the Interview Panel:-
3 female proffs (Proff. Meghna Nasre(MN), Proff. Akansha Agarwal (AA), Proff. Shweta Agarwal(SA) ) 3 male proffs of which I only know name of Proff Nishad Kothari
-It started with a lighter note, SA mam while going through my college grades asked in ur clg “E” means excellent probably right, cuz here E means fail, so i thought how can we interview this guy 😅
-then she asked why u wannna pursue ms-told abt my interest in defense technologies
MN :- " So,you have chosen algorithms , so assume there are millions of numbers, can you find the kth minimum among this "
→ I (thinking and explaining loudly), yes this can be reduced to find k th min from n elements , then i started explaining how i can make a heap and that kth minimum will be in atmax in kth level, then and there..
SA countered :-"what do you mean by level"
→then i drew a binary tree on the white board and explained the level term, she then told me to continue...here once i told something is minimum( i cannot recall the exact context)
SA mam countered “what do u mean by minimum”,
→I answered maybe some number like 100, something which is less in comparison to big number(n^n),then
AA :-" how can u compare with n^n, " then one of the other male proff countered "what if n=2, then n^n is 4 only "
SA :-" u should know these things, these are in standard textbooks only...."
→ i told if n tends to infinity then in asymptotic scale , it is big number, yet couldn’t comeup with defination of small number
now, coming back to the actual qstn, i told k th min can be in utmost kth level,we can do extract min ops to find it.
SA:-"How you so sure that the kth minimum will be in at max in the kth level"
-->I turned to the board to draw a heap and explain it
MN:-"Fine what is the TC then"
→ NOW idk how, but I made BLUNDER, i told i can do atmax 2^k extract minimum ops to find k th min in a heap !!!
The prev sir told: " u can do only in k extract minimum operations right " I realised my mistake;(,
MN:-"write the TC of this "
i wrote n+klgn which was crct
they were almost going to end the interview, but yet
MN mam asked " have u prepared any other subjects"
-->yes Mam, Data structures
MN : " what have u studied abt graphs,"
--->i told all like traversal,spanning trees...
MN: "u know djikstra algorithm right?, how can i find shortest path on a graph without using djikstra "
-->Yes we can use bfs,
MN:“gd, now what if i have some edge weights of cost 1 and some of 2,can i maybe use bfs anyway, u may tweak the graph in some sort”,
I FORGOT TO GRAB THIS HINT, ans was yeah just add dummy nodes(already learnt this from Sachin Mittal sir in his algorithms course) for edges with cost 2 and done, instead i blabbered abt how this can fail , that dummy node thought did came, but i thought will tell it later and forgot it in that heat of moment”, seeing me struggling
MN mam decreased the level of question even further, " assume all edge weights cost 1, only one edge cost 2, u cannot modify bfs, and now use it to find shortest path”, here probably they gave option to modify the graph else it was not possible to do it, but i failed again, told some counter eg, but yeah it was not correct, anyway then they were done with the interview.
Though the 1st interview of my life did not went well, basically i froze when all the professors were looking at me and I could not even think properly, yet I thought the silver lining is, now there will be less pressure on my systems interview which was scheduled on 8th May 9am.
Panel B( Computing Systems) interview experience(8th May ~9:30 am):-
Professors in the Interview Panel:- All were male professors ,Prof K Nandivada (HOD), Prof. Kartik Nagar(KN), Prof. Rupesh Nasre(RN), 2 more professors whose name i don't know.
First KN sir told abt general pattern of the interview(programming then subject)
KN:-"write structure of a node of linked list on the board"
-->wrote it
KN:-"Now find a value inside a linked list, or return null if not present"
--> i wrote the code, Mine initial code was buggy, i didn’t wrote with correct logic, like i wrongly added *head, which would result in runtime error,also i missed some part , so it would not work if list is empty, neither would it work if the value is not present,
KN:-"This code will give compilation error, runtime error, try to correct it"
--> modified the braces, other mistakes
KN:-"Yeah, now it is fine, so in the corner of the board the subject names are written which subject will you pick"
--->I will choose operating system.
---HOD sir asked all qstns from here---
q1)What is a process?
->executable program,
he exclaimed "what!!!"
-->sry sir my bad, it is a program in execution (point to note:-never make ur own definition!!)
q2)what is a thread?
->a lightweight process
q3)what is a “light weight”, how do u define lightweight, i mean in what parameter r u telling the process is lightweight?
->Sir, threads do not have their own address space, rather they have their own stack , so context switch is less costly in terms of time
q4)What is the difference between PCB and TCB?
-->Fumbled for this question, then told i thnk there is no state information(running,ready,..)for the threads
HOD sir:-"no no, thread also have those states..
-->i tried again, "then sir i think there should not have any current working directory(cwd) info inside the thread, cuz we are already having PID, so cwd of thread should be same as cwd of the process.."
q5)ok, regarding that context switch concept i have 1 question , assume uniprocessor system where a process p1 is executing now p2 wanna execute how will it happen?
->i really thought he is just asking how context switch happens, i already read abt it in details for xv6 and also Sachin Mittal sir taught it quite well in the OS introductory lecs, (but alas the actual qstn he meant was far from this)
so i told "sir interrupt will be raised then p1 will save it’s stack content…"
Hod sir countered "who will raise the interrupt?
->Sir, OS will raise it,
HOD sir:-how can the OS interrupt, it is a uniprocessor system only?
->i fumbled, i told "OS is the manager,won’t it runs always
HOD Sir(smiling):-"how can it be , it’s only uniprocessor na how OS program will run?"
-->…now i couldn’t answer, i got stuck, then for hint
HOD sir told "your interrupt thinking is crct, but there is much more to this"
..seeing i kinda got stuck,
RN:-U wanna drink some water
--->no sir, i'm fine
So Hod sir asked,
q6)what process scheduling algos have u studied
->i told fcfs, sjf,srtf,RR
q7)ok tell what happens in RR?
->told a fixed time quanta is there, after which there is Context Switch,
q8)well why will a process which let’s say computing nth prime give up CPU on it’s own, like what will ensure that
->i told that it is timer interrupt
q9)what type of intpt is it?
->made mistake!! and told it is software interrupt(i thought timer is clock which i see on screen, which is software hence software interrupt )<<----WRONG
***Then they were done with the interview
KN sir told u can rub the board and leave, while i was rubbing the board
RN:-"keep rubbing the board and try to answer this question, when we restart the pc the clock gets setup with same date and time, how is it happen"
->i told they gets synchronised somehow
HOD sir:- "but there is no internet on, how does it happen"
--> i couldn’t ans
RN :-"Well the answer of this and that prev unattempted qstn are having same concept think abt it, thank you"
And the interview was over
Actual answer:-
In computer, there is a real time clock(RTC) WHICH HELPS in this
And also timer int is HARDWARE inpt, which i didnot know(rather mugged up and forgot)
Overall experience:-
I thought my systems interview went decent. HOD sir is very chill and always tried to lighten the tensed situation. Also whenever you can't answer they decrease the level of the question further, gives hint. Also, they expect the candidates to write proper indented code with correct syntax, but anyway they asked basic coding questions only.Though at the end I was not selected for the MS program still I really cherished the experience. It was my first time visiting any IIT, interacting with the professors there and it was a memorable experience there.Ending the answer with couple of snaps i took of IIT Madras.
Theory panel interview room:-
Systems panel interview room:-
