Computer Fundamentals & Digital Logic - Complete Guide
Last Updated: August 19, 2026 | Marks Weightage: ~10 Marks | BPSC CS Teacher
A comprehensive guide covering all important topics of Computer Fundamentals and Digital Logic for the BPSC Computer Science Teacher exam.
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1. Generations of Computers
| Generation | Technology | Features | Example |
|---|---|---|---|
| 1st (1940-56) | Vacuum Tubes | Large, slow, costly, magnetic drums | ENIAC, UNIVAC |
| 2nd (1956-63) | Transistors | Smaller, faster, reliable, magnetic cores | IBM 1401 |
| 3rd (1964-71) | Integrated Circuits (ICs) | Small, efficient, multiprogramming | IBM 360 |
| 4th (1971-80) | Microprocessors | Personal computers, GUIs | Intel 4004, Apple II |
| 5th (1980-present) | ULSI, AI | Parallel processing, AI, ML | Modern PCs, Smartphones |
💡 Exam Tip: Questions often ask about technology used in each generation and the year ranges.
2. Basic Computer Organization
🧠 CPU (Central Processing Unit)
- ALU: Performs arithmetic (+, -, *, /) and logical (AND, OR, NOT) operations
- Control Unit (CU): Fetches, decodes, and executes instructions
- Registers: Small, fast memory inside CPU (Accumulator, Program Counter, Stack Pointer)
💾 Memory & I/O
- Primary Memory: RAM (Volatile), ROM (Non-volatile)
- Secondary Memory: HDD, SSD, Pen Drive, CD/DVD
- Cache Memory: High-speed memory between CPU and RAM
- I/O Devices: Keyboard, Mouse, Monitor, Printer
3. Memory Units & Hierarchy
📊 Memory Units
- Bit: 0 or 1
- Byte: 8 bits
- KB (Kilobyte): 1024 Bytes
- MB (Megabyte): 1024 KB
- GB (Gigabyte): 1024 MB
- TB (Terabyte): 1024 GB
- PB (Petabyte): 1024 TB
📌 Memory Hierarchy: Registers → Cache → RAM → Secondary Storage (HDD/SSD)
4. Number Systems
🔢 Systems
- Binary: Base 2 (0,1) - Used in computers
- Octal: Base 8 (0-7)
- Decimal: Base 10 (0-9) - Human-friendly
- Hexadecimal: Base 16 (0-9, A-F)
🔄 Conversions
- Binary to Decimal: Multiply each bit by 2^n
- Decimal to Binary: Divide by 2 repeatedly
- Binary to Hexadecimal: Group 4 bits
- Hexadecimal to Binary: Expand each hex digit
Example: (1011)₂ = 1×2³ + 0×2² + 1×2¹ + 1×2⁰ = 8 + 0 + 2 + 1 = (11)₁₀
5. Encoding Schemes
- ASCII: 7-bit encoding, 128 characters (A-Z, a-z, 0-9, symbols)
- Extended ASCII: 8-bit, 256 characters
- Unicode: 16/32-bit, supports all world languages (UTF-8, UTF-16)
- ISCII: Indian Script Code for Information Interchange
6. Boolean Algebra
📝 Basic Laws
- Identity Law: A + 0 = A, A · 1 = A
- Null Law: A + 1 = 1, A · 0 = 0
- Idempotent Law: A + A = A, A · A = A
- Complement Law: A + A' = 1, A · A' = 0
📝 Important Theorems
- De Morgan's Law: (A+B)' = A'·B' and (A·B)' = A' + B'
- Associative Law: A+(B+C) = (A+B)+C
- Distributive Law: A·(B+C) = A·B + A·C
7. Logic Gates
AND
Output 1 only when all inputs are 1
Symbol: · or ∧
OR
Output 1 when any input is 1
Symbol: + or ∨
NOT
Inverts the input
Symbol: ' or ¬
NAND
AND followed by NOT
Universal Gate
NOR
OR followed by NOT
Universal Gate
XOR
Output 1 when inputs differ
Symbol: ⊕
XNOR
Output 1 when inputs are same
Symbol: ⊙
💡 Exam Tip: NAND and NOR are called Universal Gates because any logic gate can be built using them.
8. Karnaugh Maps (K-Maps)
K-Map is a method to simplify Boolean expressions visually.
- 2-Variable K-Map: 4 cells
- 3-Variable K-Map: 8 cells
- 4-Variable K-Map: 16 cells
- Grouping: Group 1s in powers of 2 (1, 2, 4, 8)
📌 Steps: Fill K-Map → Group adjacent 1s → Write simplified expression
9. Logic Circuits
➕ Half Adder
- Adds 2 bits (A + B)
- Outputs: Sum (S), Carry (C)
- S = A ⊕ B, C = A · B
Example: 1 + 1 = 0 (Sum), 1 (Carry)
➕ Full Adder
- Adds 3 bits (A + B + Cin)
- Outputs: Sum (S), Carry (Cout)
- Built using 2 Half Adders + OR gate
🔄 Multiplexer
- Selects one input from many
- 2:1 MUX: 2 inputs, 1 select line
- 4:1 MUX: 4 inputs, 2 select lines
🔀 Decoder
- Converts encoded input to decoded output
- 2:4 Decoder: 2 inputs, 4 outputs
- 3:8 Decoder: 3 inputs, 8 outputs
10. Frequently Asked Questions
❓ What are the 5 generations of computers?
1st: Vacuum Tubes, 2nd: Transistors, 3rd: ICs, 4th: Microprocessors, 5th: ULSI/AI
❓ What is De Morgan's Law?
(A+B)' = A'·B' and (A·B)' = A' + B'
❓ What are Universal Gates?
NAND and NOR are Universal Gates.
❓ What is the difference between ASCII and Unicode?
ASCII supports 128 characters (English), Unicode supports all world languages.
