Interview Date - 12th May on Teams
Duration - 25 mins
Panelists - Madhukar Kumar, Subodh Sharma, Smruti Ranjan, Sandeep Sen.

Before the interview started they asked me what Im comfortable with and I said Systems.

  • What is Virtual Memory and why we need it?

  • Does every process require Virtual address?

Yes, explained about the security issue if we give them physical address directly. We need to provide them virtual address else we will face issue of isolation and end up accessing other process memory.

  • Who does the translation?

MMU, part of the hardware fused on-chip(CPU).
I forgot to mention about page-table walker.

  • Where is OS/Kernel involved in the above?

In case of page-faults/cache miss or external interrupts.

  • Do we need memory translation for every instruction?

Depends on TLB if we are using and also physical cache.

  • TLB? Explain miss and hit along with physical cache?

TLB + Caches + Pages

  • What is an ideal page size?

Took a random scenario and they asked for total pt overhead used pen/paper, took MM - 8 GB, Process - 8GB, PS = 4KB, explained the translation, also gave them a rough estimate of PTE and final total PT overhead

  • Does every process need a PT?


  • Do we need to flush the PT out of MM every time a new process comes in

Sc1 : If we have sufficient space in MM to accomadate the new process along with its PT then no need.
Sc2 : If MM does’nt have sufficient space then we need to swap out.
Though TLB always needs to be flushed everytime a new process is scheduled

  • Suggest another method where we can reduce PT overhead

segmentation : explained the concept of base and limit, and substantially reduce the overhead.

I missed on explaining the concept of Huge Pages which is used in Linux(THP), also we can use Inverted Page table too.

  • Quick-Sort - Give one line formal statement

I was not sure what were they expecting kind of like how will you sell QS to me, Eg. Merge sort will sort any input in O(nlogn), similarly give me a formal statement

  • How will you sort an input of Strings

I said heap sort. How will comparison happen - Lexicographically.

Few thoughts

IIT D usually always asks about Mathematics(Linear Algeabra & Probability) along with Data Structures and Algorithms. In my case the interview was more inclined towards Systems, but if someone is targeting IITD please be prepared on the above along with Logic and proofs. Whatever answer you provide they will ask you to either prove if its mathematical else why/why not?

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