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My ISRO interview was scheduled on 30th July 2018. I had joined IIT Bombay just two weeks before. Studies have started(even though not in full momentum). This interview meant a lot to me. So I prepared daily for 1–2 hours for the interview. I submitted the weekly assignments on friday and left for Delhi by train on the same night.

I reached the interview centre and found out that my number was in the end of interview list. I became worried as I had my flight at 9PM. I told them about this and they told me that they were rearrange my number. My interview began at about 4:30 in the evening. I went inside the interview room and found 9 interviewers(1 in the middle, 4 on each side). They first asked me about my favourite subjects and I replied Data structures, Networks and OS. Then the following questions were asked:

  • What were the algorithms that you used in your project
  • Explain the working of Random Forest?
  • Is Database a system or Application program( No where related to my favorite subjects)

I answered the first two questions satisfactorily but for the 3rd questions I replied application program and the interviewer(let’s call him X) looked disappointed. He immediately asked the interviewer beside him(Y) to ask the next questions. Y asked 3–4 questions from OS( which I don’ remember now). I answered them. He was satisfied and then he asked X to ask the next questions.

  • What is a tree?
  • Difference between a tree and Forest?
  • If u are given 7 nodes how many trees and forest are there?
  • What is BIOS?
  • What is firmware?
  • What is VLAN?

I explained the first 4 comfortably. For firmware he accepted the definition but not satisfied much. For the last question I told him the full form. Then I said I don’t about its working but I told him whatever I can guess from its name(It was a good guess). He started laughing from my explanation. Then he again asked Y to ask questions. Y again asked some questions from operating system like

  • How deadlocks can occur
  • How can you prevent them
  • What is a semaphore and its operations
  • What is priority inversion
  • Context switching

I answered all these questions satisfactorily. Then another interview who was sitting to the left of head started asking questions

  • What is mutation testing?

didn’t know

  • What is regression testing?


  • write code to find gcd of two numbers using Euclidean algorithm?

I had forgotten this algorithm. So I went to the whiteboard and stood there for 2 seconds and then wrote the algorithm. Then I looked towards the interviewers and they said OK

  • Now Y asked in the code that you have written which among a,b,r is the gcd?

Big problem. I knew that r is not the gcd but confused between a and b. I just stood there for 2–3 seconds and then I gave an interesting explanation. My code was


I told them that this loop is going to stop when r becomes equal to 0. Now suppose that the loop stops in the nth iteration then in the (n-1)th iteration the value stored in b would be the value of r(which means 0). Now since gcd of two numbers cannot be 0 therefore r and b are eliminated and hence a is the gcd.

At this point for the first time X and Y both were smiling. Now the head started asking questions from Computer architecture

  • What is programmed I/O?
  • What is interrupt I/O?
  • why interrupt I/O is better than programmed I/O?
  • what is daisy chaining?

I answered all of them. After I have gave the definition of daisy chaining they wanted me to tell more about it. I didn’t remember any. At this point X helped me and then I told them about priorities in daisy chaining. At this point again I felt positiveness in the interview room. There were two ladies sitting in among them and both were silent upto this point. The first one asked

  • what is optimum page size and how do you decide where a page size is good or bad?


  • What is the difference between for loop and while loop( I mean they were asking which is more powerful)?

I said no difference.

  • Then why these two are provided. why not only one?

I told that even though both are equally powerful sometimes the condition can be more naturally expressed by while and sometimes by for.

  • X asked me to go to the whiteboard write the program that I have already written but using for loop

I did that and all were satisfied. Now the 2nd lady asked something about memory management. I asked thrice to repeat the question or explain it more but I was unable to interpret what she was asking. In the end I gave a half hearted answer. Then she asked

  • How is multiplication done in computers?

I told her Booth Algorithm. Then I was told that the interview was over.

Some tips for ISRO interview:

  • I felt that they check the breadth of knowledge and not depth
  • You can use Hindi as well as English during the interview. I initially started in English but got stuck at some point and asked them if I could use Hindi. They said of course. Now during the later part of interview for a few questions they asked me to explain in English. I felt that they were trying to test me and then I gave the answers in English
  • Don’t worry if your interview starts badly. Mine started in a bad way but it ended on high note.
  • Even if you don’t know the exact answer to the question don’t just say I don’t know. Instead tell them you don’t know completely but you have some idea(if you really do) and then try to explain that idea. Happened to me in that VLAN question. However if you don’t have the slightest idea then just plainly say that you don’t know
  • Your presence of mind can help you a lot.

Interview result: Rank 2 in the merit list

81.38 scored out of 100.

Best of luck to future candidates.

Thank you.

posted Aug 31, 2018 in Interview Experience by
edited Sep 13, 2018 by | 1,251 views


Congratulations Acheiver! Your interview grasped more breadth than mine which makes your success more beautiful.

Surprised to find out that we were interviewed the same day :p
congratulations to both of [email protected] @mamta...really great work.
congrats bro, can u tell how much marks u scored in 10th plus two and graduation. Just wanted to know whether there is any waitage..
Did you not notice the tallest guy present there? That was me.
@Kishan, How many marks you got in the interview ? Please share if you don't mind...
My marks were 81.38 out of 100
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