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CS Fundamentals

~8 min

In short

Core CS questions come up in many software interviews, campus rounds included. The exact mix depends on the company and the role, and no company publishes its question list, so this section does not claim one. It gives you a checklist of questions an interviewer can reasonably ask, short notes on the key ideas, and one practice task per subject. Answer the checklist out loud. Reading the answers is not the same thing as being able to give them.

The four subjects

Subject Page What it covers
Operating systems 01-os.md Processes, threads, scheduling, synchronisation, deadlock, memory
DBMS and SQL 02-dbms-sql.md Keys, normalisation, indexes, joins, transactions, isolation, practice queries
Computer networks 03-networks.md TCP and UDP, HTTP, DNS, TLS, what happens when you type a URL
OOP and design basics 04-oop-and-design-basics.md Four pillars, SOLID basics, a parking lot design exercise

How to use these pages

  1. Read the key ideas once, then close the page.
  2. Answer each checklist question aloud, in your own words, without notes. Time yourself. A useful target for a first attempt is under two minutes per question (author's guidance, not a standard).
  3. Mark the questions you stumbled on. Revisit only those, the next day.
  4. Do the task in the Try this section for each subject.

Keep one notes file with a line per question you got wrong. Read it before each practice session.

Go deeper

When a key idea is new to you, read the matching core subjects page first, then come back here:

What the interviewer is checking

Across all four subjects, the same three things come up. Interviewers want to know whether you can define a term in one sentence, whether you can say why it exists, and whether you can give a small example. A good answer to "what is a deadlock?" names the cause, the four conditions, and one way to avoid it. A memorised definition with no reason behind it usually leads to a follow-up that exposes the gap.

Expect follow-ups such as "why", "what if", and "how would you test that". Practise answering them, not only the first question.

Suggested order

If you have one week, do the subjects in the order that matches your weakest area. If you are unsure, start with DBMS and SQL, because SQL is the most hands-on and the queries give you immediate feedback. Then move to operating systems, networks and OOP. Spend the last sessions on the questions you marked during practice, not on re-reading whole pages.

Whatever order you choose, keep the time short and frequent. Twenty focused minutes a day on answering aloud will usually do more than one long reading session. (Author's guidance.)

Honest limits

Nothing on these pages can tell you which questions you will be asked, and knowing them does not ensure an offer. Treat the checklists as a way to find gaps, not as a list of answers to memorise.

Try this

Pick one checklist question from each of the four subjects. Answer each aloud for 90 seconds, record yourself on your phone, and listen back. Write down the one point where you went quiet or used a vague word like "something like".

Sources