Core CS & Web Fundamentals

For most high-level backend engineering, the underlying transport layers and operating system mechanics are heavily abstracted. However, when performance degrades, memory leaks occur, or you are designing low-latency distributed systems, understanding how computers actually communicate and manage hardware resources becomes critical.

Top-tier companies frequently test these fundamentals to ensure candidates understand what happens "under the hood."

Networking & Web

• The OSI Model: The 7 layers of network abstraction (from wires to APIs).
• TCP vs UDP (Layer 4): Reliable handshakes vs. reckless speed.
• Routing (DNS & BGP): How domains are resolved and packets are routed globally.
• HTTP vs HTTPS (TLS): Deep dive into the TLS handshake and asymmetric encryption.
• Web Security (OWASP): Mitigating XSS, CSRF, SQLi, and understanding CORS.

Operating Systems & Code Execution

• Code Execution: Compilers, Interpreters, and JIT (Just-In-Time) compilation.
• Memory Management: Virtual memory, paging, and preventing thrashing.
• CPU Scheduling: How the OS decides which process runs next.
• File Systems & I/O: Inodes, journaling, and disk performance.

"There is no cloud, it's just someone else's computer. And that computer runs an OS connected to a router."