Computer Organization Lab Manual: 100 Practical Viva
Questions and Answers with Detailed Rationales Across
10 Experiments
Experiment 1: Number Systems and Number Conversions
Questions 1–10 | Binary, decimal, octal, hexadecimal, and arithmetic
Q1. What is a number system?
Answer: A number system is a method of representing numbers using a set of symbols and rules.
Rationale: Different number systems use different bases. For example, decimal uses base 10,
while binary uses base 2.
Q2. What is the base or radix of the binary number system?
Answer: The base is 2.
Rationale: Binary uses only two digits, 0 and 1, which correspond to the two basic logical states
used in digital circuits.
Q3. Convert \((1011)_2\) to decimal.
Answer: \((1011)_2 = (11)_{10}\).
Rationale:
\[ 1(2^3)+0(2^2)+1(2^1)+1(2^0) =8+0+2+1=11 \]
Q4. Convert decimal 25 to binary.
Answer: \((25)_{10}=(11001)_2\).
Rationale: Express 25 as powers of two: \(16+8+1=25\). Therefore, the binary digits are 11001.
Q5. What is the base of the hexadecimal number system?
Answer: Base 16.
Rationale: Hexadecimal uses digits 0–9 and letters A–F, where A represents 10 and F represents
15.
,Q6. Convert \((2F)_{16}\) to decimal.
Answer: \((2F)_{16}=(47)_{10}\).
Rationale:
\[ 2(16^1)+15(16^0)=32+15=47 \]
Q7. What is the binary equivalent of hexadecimal A?
Answer: \(1010_2\).
Rationale: Hexadecimal A represents decimal 10, which is 1010 in four-bit binary.
Q8. Perform the binary addition \(101_2+011_2\).
Answer: \(1000_2\).
Rationale: Binary 101 represents 5, and 011 represents 3. Their sum is 8, which is 1000 in
binary.
Q9. What is a bit?
Answer: A bit is the smallest unit of digital information and can have a value of 0 or 1.
Rationale: Bits represent binary information processed and stored by digital computer systems.
Q10. Why is hexadecimal commonly used in computer organization?
Answer: It provides a compact representation of binary values.
Rationale: One hexadecimal digit represents exactly four binary bits, making long binary
sequences easier to read and write.
Experiment 2: Logic Gates and Truth Tables
Questions 11–20 | AND, OR, NOT, NAND, NOR, XOR, and XNOR
Q11. What is a logic gate?
Answer: A logic gate is a digital circuit that performs a Boolean operation on one or more inputs.
Rationale: Logic gates are the fundamental building blocks of digital systems, including
processors, registers, and arithmetic circuits.
Q12. What is the output of an AND gate when both inputs are 1?
, Answer: 1.
Rationale: An AND gate outputs 1 only when all its inputs are 1.
Q13. What is the output of an OR gate when both inputs are 0?
Answer: 0.
Rationale: An OR gate outputs 1 if at least one input is 1; otherwise, it outputs 0.
Q14. What does a NOT gate do?
Answer: It inverts the input.
Rationale: If the input is 0, the output is 1. If the input is 1, the output is 0.
Q15. Why is a NAND gate called a universal gate?
Answer: Because any Boolean function can be implemented using NAND gates alone.
Rationale: NAND gates can be combined to construct NOT, AND, OR, and more complex logic
circuits.
Q16. What is the output of a NOR gate when inputs are A = 0 and B = 0?
Answer: 1.
Rationale: A NOR gate is the complement of an OR gate. Since \(0+0=0\), the NOR output is 1.
Q17. What is the output of an XOR gate when A = 1 and B = 1?
Answer: 0.
Rationale: XOR outputs 1 only when its inputs differ. Equal inputs produce 0.
Q18. What is the difference between XOR and XNOR?
Answer: XOR outputs 1 when inputs differ, while XNOR outputs 1 when inputs are equal.
Rationale: XNOR is the logical complement of XOR and is useful in equality comparison
circuits.
Q19. Write the Boolean expression for a two-input AND gate.
Answer: \(Y=A\cdot B\).
Questions and Answers with Detailed Rationales Across
10 Experiments
Experiment 1: Number Systems and Number Conversions
Questions 1–10 | Binary, decimal, octal, hexadecimal, and arithmetic
Q1. What is a number system?
Answer: A number system is a method of representing numbers using a set of symbols and rules.
Rationale: Different number systems use different bases. For example, decimal uses base 10,
while binary uses base 2.
Q2. What is the base or radix of the binary number system?
Answer: The base is 2.
Rationale: Binary uses only two digits, 0 and 1, which correspond to the two basic logical states
used in digital circuits.
Q3. Convert \((1011)_2\) to decimal.
Answer: \((1011)_2 = (11)_{10}\).
Rationale:
\[ 1(2^3)+0(2^2)+1(2^1)+1(2^0) =8+0+2+1=11 \]
Q4. Convert decimal 25 to binary.
Answer: \((25)_{10}=(11001)_2\).
Rationale: Express 25 as powers of two: \(16+8+1=25\). Therefore, the binary digits are 11001.
Q5. What is the base of the hexadecimal number system?
Answer: Base 16.
Rationale: Hexadecimal uses digits 0–9 and letters A–F, where A represents 10 and F represents
15.
,Q6. Convert \((2F)_{16}\) to decimal.
Answer: \((2F)_{16}=(47)_{10}\).
Rationale:
\[ 2(16^1)+15(16^0)=32+15=47 \]
Q7. What is the binary equivalent of hexadecimal A?
Answer: \(1010_2\).
Rationale: Hexadecimal A represents decimal 10, which is 1010 in four-bit binary.
Q8. Perform the binary addition \(101_2+011_2\).
Answer: \(1000_2\).
Rationale: Binary 101 represents 5, and 011 represents 3. Their sum is 8, which is 1000 in
binary.
Q9. What is a bit?
Answer: A bit is the smallest unit of digital information and can have a value of 0 or 1.
Rationale: Bits represent binary information processed and stored by digital computer systems.
Q10. Why is hexadecimal commonly used in computer organization?
Answer: It provides a compact representation of binary values.
Rationale: One hexadecimal digit represents exactly four binary bits, making long binary
sequences easier to read and write.
Experiment 2: Logic Gates and Truth Tables
Questions 11–20 | AND, OR, NOT, NAND, NOR, XOR, and XNOR
Q11. What is a logic gate?
Answer: A logic gate is a digital circuit that performs a Boolean operation on one or more inputs.
Rationale: Logic gates are the fundamental building blocks of digital systems, including
processors, registers, and arithmetic circuits.
Q12. What is the output of an AND gate when both inputs are 1?
, Answer: 1.
Rationale: An AND gate outputs 1 only when all its inputs are 1.
Q13. What is the output of an OR gate when both inputs are 0?
Answer: 0.
Rationale: An OR gate outputs 1 if at least one input is 1; otherwise, it outputs 0.
Q14. What does a NOT gate do?
Answer: It inverts the input.
Rationale: If the input is 0, the output is 1. If the input is 1, the output is 0.
Q15. Why is a NAND gate called a universal gate?
Answer: Because any Boolean function can be implemented using NAND gates alone.
Rationale: NAND gates can be combined to construct NOT, AND, OR, and more complex logic
circuits.
Q16. What is the output of a NOR gate when inputs are A = 0 and B = 0?
Answer: 1.
Rationale: A NOR gate is the complement of an OR gate. Since \(0+0=0\), the NOR output is 1.
Q17. What is the output of an XOR gate when A = 1 and B = 1?
Answer: 0.
Rationale: XOR outputs 1 only when its inputs differ. Equal inputs produce 0.
Q18. What is the difference between XOR and XNOR?
Answer: XOR outputs 1 when inputs differ, while XNOR outputs 1 when inputs are equal.
Rationale: XNOR is the logical complement of XOR and is useful in equality comparison
circuits.
Q19. Write the Boolean expression for a two-input AND gate.
Answer: \(Y=A\cdot B\).
