76. Joining both inputs of a NAND gate together makes a:
- OR gate
- NOT gate
- buffer
- AND gate
Answer: B) NOT gate
Explanation: (A·A)' = A', so a NAND with both inputs tied is an inverter. SLO CS-11-A-01
MCQs / Computer Science / Unit 1: Computer Systems
Unit 1: Computer Systems MCQs — Computer Science (page 4)
100 multiple-choice questions on Unit 1: Computer Systems from Computer Science, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.
77. Which signal can take only a limited number of discrete values?
- Analog
- Sound wave
- Digital
- Sine wave
Answer: C) Digital
Explanation: Digital signals use discrete levels (0 and 1); analog signals are continuous. SLO CS-11-A-01
78. The simplified form of F = AB + AB' is:
- A
- AB
- 1
- B
Answer: A) A
Explanation: F = A(B + B') = A · 1 = A. SLO CS-11-A-01
79. Which expression represents a NAND gate?
- A + B
- (A + B)'
- (AB)'
- A'B'
Answer: C) (AB)'
Explanation: NAND is NOT-AND: (AB)'. By De Morgan it also equals A' + B'. SLO CS-11-A-01
80. Which gates are called universal gates?
- XOR and XNOR
- NAND and NOR
- NOT and AND
- AND and OR
Answer: B) NAND and NOR
Explanation: Any logic function can be built using only NAND gates or only NOR gates. SLO CS-11-A-01
81. How many rows does the truth table of a 3-input logic expression have?
- 6
- 3
- 8
- 9
Answer: C) 8
Explanation: With n inputs there are 2^n combinations: 2^3 = 8 rows. SLO CS-11-A-01
82. Injecting a malicious script into a web page so that it runs in other users' browsers is:
- brute force
- a firewall rule
- cross-site scripting (XSS)
- DDoS
Answer: C) cross-site scripting (XSS)
Explanation: XSS injects scripts through unvalidated input. SLO CS-11-A-04
83. Which topology is the most reliable because it offers multiple paths between nodes?
- Star
- Ring
- Mesh
- Bus
Answer: C) Mesh
Explanation: Mesh has redundant links, so data can take another path if one fails. SLO CS-11-A-03
84. The main weakness of symmetric encryption is:
- it is too slow
- it cannot encrypt text
- the secret key must be shared safely
- it uses two keys
Answer: C) the secret key must be shared safely
Explanation: Both sides need the same key, so key distribution is the problem. SLO CS-11-A-04
85. The dual of A + 0 = A is:
- A · 0 = 0
- A · 1 = A
- A + 1 = 1
- A' + 0 = A'
Answer: B) A · 1 = A
Explanation: Duality swaps AND with OR and 0 with 1, keeping the variables: A · 1 = A. SLO CS-11-A-01
86. Malware that encrypts your files and demands payment is:
- spyware
- a worm
- ransomware
- adware
Answer: C) ransomware
Explanation: Ransomware holds files to ransom. SLO CS-11-A-04
87. Which SDLC phase produces the Software Requirements Specification (SRS)?
- Coding
- Requirement analysis
- Planning
- Maintenance
Answer: B) Requirement analysis
Explanation: Requirements gathered from users are documented in the SRS during analysis. SLO CS-11-A-02
88. Which identity is correct?
- A · A' = 1
- A + 1 = 1
- A · 1 = 1
- A + A' = 0
Answer: B) A + 1 = 1
Explanation: Null law: anything OR 1 is 1. A + A' = 1, A·A' = 0 and A·1 = A. SLO CS-11-A-01
89. Which type of encryption uses a public key and a private key?
- Caesar
- Symmetric
- Hashing
- Asymmetric
Answer: D) Asymmetric
Explanation: Asymmetric (public-key) encryption uses a key pair. SLO CS-11-A-04
90. Using a password and an OTP sent to your phone is an example of:
- hashing
- encryption
- two-factor authentication
- authorization
Answer: C) two-factor authentication
Explanation: Two different factors – something you know and something you have. SLO CS-11-A-04
91. In Waterfall, a change in requirements discovered during testing is:
- cheap to make
- expensive, because earlier phases must be redone
- impossible
- handled in the next sprint
Answer: B) expensive, because earlier phases must be redone
Explanation: Waterfall phases are sequential, so going back is costly. SLO CS-11-A-02
92. Making the software work on a new version of the operating system is which type of maintenance?
- Corrective
- Adaptive
- Preventive
- Perfective
Answer: B) Adaptive
Explanation: Adaptive maintenance adapts software to a changed environment. SLO CS-11-A-02
93. Which statement about hashing is TRUE?
- It can be reversed with a key
- It is one-way and gives a fixed-length output
- It needs a public key
- It is used only for large videos
Answer: B) It is one-way and gives a fixed-length output
Explanation: A hash cannot be reversed and always has the same length (e.g. SHA-256 = 256 bits). SLO CS-11-A-04
94. A cloud service that adds servers automatically when traffic increases shows:
- token passing
- redundancy only
- duality
- elasticity (auto-scaling)
Answer: D) elasticity (auto-scaling)
Explanation: Auto-scaling (elasticity) is how cloud computing provides scalability. SLO CS-11-A-03
95. "Five nines" availability (99.999%) allows about how much downtime per year?
- 5 seconds
- 52 minutes
- 5 minutes
- 5 hours
Answer: C) 5 minutes
Explanation: 0.001% of 525 600 minutes ≈ 5.26 minutes. SLO CS-11-A-03
96. F = XYZ + XY'Z + X'Z simplifies to:
- X + Z
- X
- Z
- XZ
Answer: C) Z
Explanation: XZ(Y + Y') + X'Z = XZ + X'Z = Z(X + X') = Z. SLO CS-11-A-01
97. A K-map group of four cells in a 3-variable map leaves how many variables in its term?
- 1
- 2
- 4
- 3
Answer: A) 1
Explanation: Each doubling of a group removes one variable: 3 − 2 = 1 variable remains. SLO CS-11-A-01
98. Which model is most suitable for a project whose requirements are fixed and well understood, such as building construction?
- Prototyping
- Waterfall
- Agile
- Scrum
Answer: B) Waterfall
Explanation: Waterfall works best when requirements are stable and the phases are sequential. SLO CS-11-A-02
99. A bank wants to run the new and old systems together until the new one is proven. This changeover is:
- direct
- parallel
- phased
- pilot
Answer: B) parallel
Explanation: Parallel running is safest for critical data but most expensive. SLO CS-11-A-02
100. In which testing does the tester NOT know the internal code?
- Black-box testing
- Unit testing by the programmer
- White-box testing
- Code review
Answer: A) Black-box testing
Explanation: Black-box testing checks inputs and outputs against the specification only. SLO CS-11-A-02
Previous Page 4 of 4
Practise Unit 1: Computer Systems MCQs
More Computer Science chapters
- Introduction and History of Computers MCQs
- Introduction to Mobile Applications and Platforms MCQs
- Unit 2: Computational Thinking and Algorithms MCQs
- Types of Computers and Basic Operations MCQs
- HTML5 for Mobiles MCQs
- Unit 3: Programming Fundamentals MCQs
- Input and Output Devices MCQs
- Android OS: Architecture, Framework and Application Development MCQs
- Unit 4: Data and Analysis MCQs
- Storage Units and Memory MCQs
- iOS: Architecture and Framework MCQs
- Unit 5: Application of Computer Science MCQs