My DRDO interview was scheduled on 28th August, 2018 at Recruitment and Assessment Centre(RAC). I had to reach there before 9 AM. I had problems reaching there as address mentioned on call letter was RAC, Timarpur. Some post on google mentioned the distance between New Delhi Metro Station and Timarpur as 3KM. I came outside New Delhi Metro station only to find that Timarpur was about 10 kms away. I faced problems in finding auto for that place. I was able to reach RAC just a few minutes before the scheduled time(9AM). For future candidates the best way to reach Timarpur is Vishwavidyalaya Metro Station.
I went inside to find only two candidates and that too from some other branch. After some time we were asked to sign on attendance register and provided with a pass(mine was 007). We were asked to deposit our phones at the reception counter. From the attendance register I found that only one candidate attended the interview on 27th August. Most of the absentees were people who had been selected at IOCL and even the single attendee was IOCL selected candidate(but temp unfit). The attendance register also mentioned the room number where I was to be interviewed. There was a waiting room outside that room where we were asked to verify our documents. The process took only 5 minutes. After that I was asked to sit and wait for the call. I was called for interview after 5 minutes.
I went inside to find only 5 interviewers. I greeted them and they asked me to sit. From left to right let’s call them A,B,C,D,E. C first asked about my college. As I was replying he was looking at my certificates and then he said you have read operations research and Compiler design. I said yes and then he asked if he can ask something from Operations research. I told him that I don’t remember anything from that subject. Then he ask if he can ask from Compiler design and I had to say yes(Compiler is the subject that I never touched after appearing for GATE and hence I didn’t remember much. But I had to say yes cause I had already said no to the first subject that they asked for). Then they asked if I remember DBMS and OS. I said yes and now the first question came from E
- What is real time system?
I told her the definition of hard real time system(a big mistake).
- Give two examples of real time system from daily life?
Again thinking about hard real time systems. After 2–3 seconds E started telling me example of railway reservation system as an example of (soft) real time example. As I was thinking about hard real time system I wanted to interrupt her and say that I don’t agree. But she didn’t notice that and only stopped after her full explanation. However D noticed that maybe I was not in agreement and as soon as E finished D asked me “Do you agree with her ?”. I said no and D started smiling and then asked me to explain what is the reason. I gave the reason but E countered my reasons. Both E and I were correct in their places. But the problem was that I was telling about hard real time system ans E’s example was a soft real time system. After E counter reasoning I started my counter reasoning and used the term latency. E stopped me and asked
I told her the proper definition.
- Difference between waiting time and latency?
I had told the definition of waiting time when E interrupted and provided this scenario:
- Imagine you have gone to a restaurant and you have given your order to the waiter. What is the waiting time and latency in this case?
I said that the time interval between arrival at the restaurant and arrival of waiter is waiting time. The time interval between taking order and order arrival is the latency. E agreed with me. Now C asked
- What is Gaussian elimination?
I felt that I know this but I was not able to recall anything. Finally I asked C to provide me a hint and he said matrix and I told him that Gaussian elimination is used to find the rank of a matrix. C didn’t agree and I was taken aback. Now he gave me a pen and asked me to write something on paper. He asked me to write an equation Ax=b. Now he asked me how to solve this. I told him that this is a system of linear equations and we can solve it using determinant of A and then also some other determinants(by replacing columns of A with b). He didn’t agree and again I was taken aback. Then he gave me the dimensions of A and asked to find the dimensions of x and b. I did and then he asked again how to solve these equations. Now I remembered another use of Gaussian elimination and I told him about Gaussian elimination and then he asked me the steps. I told him that I don’t remember clearly but told him about conversion to triangular matrices and then using the values among diagonals. E said OK. Now E asked
- What are the significant programs that you have written till date?
I have done 5–6 projects but I told her about my B tech project. Then they asked me various things related to the project and I was able to answer satisfactorily. After all this, E asked
- Given two programs how do you check which is better?
I told about time and space complexity. E asked to explain about how time complexity is a measure and I gave her a proper example. Now came the part which ruined my interview. C started asking questions from compiler design.
I told the full form Yet another compiler compiler. But C started smiling and said compiler compiler does not make any sense. I knew what YACC does but was not fully confident about this. So I stayed mum. Now C asked
- Top down vs Bottom up parsing
I told him that Bottom up parsers are more powerful than top down parsers and he looked surprised. He asked me how can you say this and I replied about LR and LL parsers. Then he asked me where did you read that Bottom up parsers are more powerful than top down parsers. I told him the name of the book Aho and Ullman. Then he asked me to prove that bottom up parsers are more powerful than top down parsers and I said I don’t know. Then he asked explaining that he was asking me bottom up vs top down parsers in general but you have given me examples of LL and LR which don’t cover all cases. C was too much enthusiastic about compiler design. If possible he would have asked me everything from compiler. I told him politely that I haven’t studied this subject in depth. Still he asked questions about syntax checking and three address code. I told him whatever I knew. Whatever interviews I have given till date this was the first time that I felt so much uncomfortable. At one point my throat went dry and I was not able to articulate my words properly. Water bottle was there on the table but since it was closer to C I preferred not to take it. When C was done with all his compiler-giri B asked me
I gave the first definition and B looked surprised. Then I gave another definition. Finally satisfied. He then asked
- Write a program for bubble sort in python
Did
- Time complexity of this program
Told him
- How are functions written in python
Told him about indentation.
- Draw the graph of n^2, n and logn?
Did
- Point of intersection of n and logn?
Unable to find any such point. Now A asked
Explained.
- What are TCP/IP layers and difference between OSI and TCP?
Explained.
- Different types of RAM and ROM.
I explained everything. Now D asked
- What technology is used in hard disk?
Told him about metal oxide.
- What technology is used in memory cards?
Told him that it is the same as EEPROM with some minor differences. But he wanted to know the basic technology. I first told IC and then transistor. Now C asked
- What is von neumann architecture?
Explained.
- What is von neumann bottleneck?
Explained but they were not convinced. E asked
- Difference between error and bug?
I didn’t know.
- What is segmentation fault?
Explained.
Some more questions were asked but I have forgotten them. In last they asked my opinion on whether I am ready to work as a Scientist. Then D told me that your college ended in June and this is August. What were you doing for the last 2 months. I told them I am doing M tech at IIT Bombay. He looked shocked(Best part of Interview). After this I was asked to leave.
I have not prepared for this interview. But didn’t expect it to be that bad. I was not able to build any sort of momentum throughout the interview. And the main problem was that they asked from compiler design(I don’t like this subject).
