Computer Fundamentals and Operating Systems
Core concepts
A candidate must be fluent in number systems and conversion (binary, octal, decimal, hexadecimal), two's complement representation of signed integers, character encodings (ASCII, Unicode/UTF-8), and the layered structure of a computer: CPU (ALU, control unit, registers), memory hierarchy (registers, cache, RAM, secondary storage), and I/O. Understand stored-program execution: fetch-decode-execute, instruction cycle, addressing modes, and the distinction between RISC and CISC.
On the operating-system side, master process states and scheduling (FCFS, SJF, round robin, priority), context switching, threads versus processes, deadlock conditions and avoidance (Banker's algorithm), memory management (paging, segmentation, virtual memory, thrashing), file systems, and disk scheduling. Know the difference between internal and external fragmentation.
Traps to watch
- Confusing logical (virtual) addresses with physical addresses; page size is fixed, segment size is not.
- Mixing up throughput and turnaround time in scheduling questions.
- Assuming 1 KB always equals 1000 bytes; in exams it is usually 1024 unless stated.
- Forgetting that deadlock requires all four Coffman conditions simultaneously.
Worked example
Convert decimal 45 to binary: divide by 2 repeatedly, reading remainders upward gives 101101. Two's complement of 8-bit +5 (00000101) is 11111011 for -5. Rule of thumb: in an n-bit two's complement system, the range is -2^(n-1) to 2^(n-1)-1, so 8 bits give -128 to 127.