Computer Science (NEB Grade 12)
This domain covers the full NEB Grade 12 Computer Science syllabus: number systems and Boolean logic, computer architecture, data communication and networking, database management, C and object-oriented programming, web technology, software process models, and recent trends. Questions mix short definitions, "difference between" tables, trace-the-output code, and numerical conversions, so exact terminology earns marks.
Core rules
- Number systems: binary, octal, decimal and hexadecimal conversions; 1's and 2's complement; signed range for n bits is −2^(n−1) to 2^(n−1)−1.
- Boolean algebra: De Morgan's laws, canonical SOP/POS forms, Karnaugh-map groups in powers of two.
- Architecture: fetch–decode–execute cycle, registers (PC, IR, MAR, MBR), cache vs main memory vs secondary storage, RISC vs CISC.
- Networking: OSI seven layers and the TCP/IP model, device-to-layer mapping (hub L1, switch L2, router L3), IPv4 classes, basic subnetting.
- DBMS: candidate, primary and foreign keys; entity and referential integrity; 1NF to 3NF; SQL DDL vs DML.
- Programming: C data types, arrays, pointers, functions, file handling; OOP encapsulation, inheritance, polymorphism and abstraction.
Worked example
Represent −5 in 8-bit two's complement and add +3. +5 = 00000101; invert → 11111010; add 1 → 11111011, which is −5. +3 = 00000011. Sum: 11111011 + 00000011 = 11111110. The leading bit is 1, so invert and add 1 to read the magnitude: 00000001 + 1 = 00000010 = 2, giving −2. There is no carry conflict into the sign bit, so no overflow occurs.
Traps
- Writing −5 as 10000101 (sign-magnitude) when two's complement is required.
- Claiming a switch routes between different networks; it forwards frames by MAC address inside a LAN.
- Confusing a candidate key with the primary key, or allowing NULL in a primary key.
- Ignoring integer division and array index bounds in C trace questions.
- Listing OSI layers out of order or mixing TCP/IP application-layer protocols into transport.