CS Fundamentals Interview Questions: OOP, OS and Networks

Encapsulation (hiding data inside objects), abstraction (showing only what is needed), inheritance (reusing a parent's behaviour) and polymorphism (one interface, many forms). Give a small example of each.

A process is a running program with its own memory. Threads live inside a process and share its memory, which makes them lighter but needs care to avoid clashes.

Two or more processes each hold a resource and wait for another's, so none can continue. It needs mutual exclusion, hold and wait, no pre-emption and circular wait. Break one of these, for example by always taking locks in the same order.

A technique that lets a program use more memory than the computer physically has by moving unused pages between RAM and disk. It also isolates programs from each other.

TCP is reliable, ordered and connection-based, used for web pages and email. UDP is faster with no delivery guarantee, used for video calls and games.

Physical, data link, network, transport, session, presentation and application. Be ready to place familiar things on them, such as IP on the network layer and HTTP on the application layer.

A way for programs to talk over HTTP using URLs for things and methods such as GET, POST, PUT and DELETE for actions. Each request carries all it needs, and data is often sent as JSON.

A compiler translates the whole program to machine code before it runs. An interpreter reads and runs it line by line. Many languages, such as Java and Python, use a mix.

The stack holds function calls and local variables and is fast and automatically managed. The heap holds objects that live longer and is managed by the programmer or a garbage collector.

Git tracks changes to code. Merge joins two branches and keeps both histories, while rebase replays your commits on top of another branch for a straight history. Do not rebase shared branches.

SQL databases store data in tables with a fixed structure and relations. NoSQL databases, such as document or key-value stores, are more flexible and scale across machines easily. Choose by the data and the queries.

Authentication checks who you are, for example with a password. Authorisation decides what you are allowed to do once you are known.