The core-subject rounds common in campus hiring and still used to probe depth in experienced interviews.
11 published across 6 topics.
CS fundamentals59 short answers on one page, for revising rather than studying.Processes and threads, scheduling, virtual memory and paging, synchronisation, and deadlock handling.
A context switch saves the running thread's registers and program counter, lets the kernel scheduler choose another runnable thread, and restores that thread's state; the dominant cost is usually the cache and TLB pollution afterwards rather than the save and restore itself.
Virtual memory gives each process a private address space that the MMU translates to physical frames, so processes are isolated and memory is committed lazily. A missing page traps to the kernel, which either maps a frame cheaply or reads from disk - a difference of five orders of magnitude.
The layered model, TCP versus UDP, congestion control, routing, and what happens when you load a URL.
TCP guarantees an ordered byte stream and pays for it with head-of-line blocking and retransmissions that arrive too late to be useful. UDP is right when a late packet is worthless, when you need multicast, or when you intend to build your own reliability with different trade-offs.
The browser checks its caches, resolves the hostname through browser, OS and resolver caches, opens a TCP connection, completes a TLS handshake, sends the request, then parses the streamed response. QUIC fuses transport and crypto setup into one round trip and stops one lost packet stalling every stream.
Relational algebra, functional dependencies, normal forms, and concurrency-control theory.
Normalisation removes redundancy so a fact is stored once; 3NF is reached when every non-key column depends on the key and nothing but the key. You denormalise knowingly, to buy read performance with write complexity. ACID guarantees far less than candidates assume, particularly its C.
A schedule is serialisable when its effect matches running the same transactions one after another in some order, which is the criterion isolation is defined against. Two-phase locking achieves it by forbidding a transaction from acquiring any lock after releasing one, and the price is deadlock.
Abstraction and the classical definitions, plus the terminology questions asked verbatim in screens.
Encapsulation, inheritance, polymorphism and abstraction are worth stating as consequences rather than definitions - what each one buys you and what it costs. Abstraction decides what a type means to its caller; encapsulation protects how that meaning is upheld.
The compiler cannot know, so it emits an indirect call through a per-class table of function pointers that the object carries a reference to. The lookup itself is a couple of memory accesses; the real cost is the optimisations the compiler cannot perform when the target is not known until run time.
Compilation phases, interpretation versus JIT, memory layout, and garbage-collection theory.
Source is tokenised, parsed, checked, lowered to an intermediate representation, optimised and emitted - either ahead of time to machine code or to bytecode executed by a runtime. A JIT compiles hot bytecode at run time using profiles, which is why managed programs get faster after warm-up.
OWASP categories, cryptography basics, hashing versus encryption, and secure-by-default habits.
A certificate binds a public key to a domain name and is signed by a chain ending at a root already in your device's trust store. It proves that whoever holds the matching private key controlled that name at issuance - nothing about the operator's honesty - and revoking it early barely works.
Encryption is reversible, so a key compromise exposes every password at once; hashing has no key to steal. A password hash additionally has to be deliberately slow and memory-hard, because the attacker's advantage is throughput and a general-purpose hash like SHA-256 lets them try billions of candidates per second.