MCQs / Computer Science / Unit 1: Computer Systems

Unit 1: Computer Systems MCQs — Computer Science (page 2)

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.

26. Simplify F = AB + AoverlineB.

  1. A
  2. A + B
  3. AB
  4. B

Answer: A) A

Explanation: F = A(B + overlineB) = A 1 = A. SLO CS-11-A-01 · Application

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27. A server was up for 8,750 hours and down for 10 hours in a year. Its availability is closest to:

  1. 87.5%
  2. 98.9%
  3. 99.1%
  4. 99.89%

Answer: D) 99.89%

Explanation: Availability = dfrac uptime uptime + downtime 100 = dfrac87508760 100 approx 99.89%. SLO CS-11-A-03 · Application

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28. For a two-input NAND gate, which input combination gives output 0?

  1. A = 1, B = 0
  2. A = 0, B = 1
  3. A = 0, B = 0
  4. A = 1, B = 1

Answer: D) A = 1, B = 1

Explanation: NAND = NOT(AND). AND is 1 only for 11, so NAND is 0 only for 11. SLO CS-11-A-01 · Understanding

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29. Adding more servers to share the load of a website is called:

  1. Vertical scaling (scaling up)
  2. Horizontal scaling (scaling out)
  3. Load shedding
  4. Downscaling

Answer: B) Horizontal scaling (scaling out)

Explanation: Horizontal scaling adds machines; vertical scaling adds power (CPU/RAM) to one machine. SLO CS-11-A-03 · Understanding

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30. Using a Caesar cipher with a shift of 3, the plaintext CAB becomes:

  1. ZXY
  2. DBC
  3. FED
  4. FDE

Answer: D) FDE

Explanation: Shift each letter 3 places forward: C→F, A→D, B→E. SLO CS-11-A-04 · Application

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31. A topology with a hierarchy of star networks connected to a root node is called:

  1. Point-to-point
  2. Ring
  3. Bus
  4. Tree

Answer: D) Tree

Explanation: Tree (hierarchical) topology connects groups of star networks to a backbone/root. SLO CS-11-A-03 · Knowledge

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32. In which SDLC phase are the users' requirements gathered and documented?

  1. Coding
  2. Analysis (requirements)
  3. Maintenance
  4. Testing

Answer: B) Analysis (requirements)

Explanation: The analysis phase studies the problem and records what the system must do. SLO CS-11-A-02 · Knowledge

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33. Hashing is mainly used to store passwords because:

  1. It makes the password longer
  2. It compresses the password to save space
  3. It can be reversed with a public key
  4. It is one-way — the original password cannot easily be recovered from the hash

Answer: D) It is one-way — the original password cannot easily be recovered from the hash

Explanation: Systems store the hash; at login they hash the typed password and compare. SLO CS-11-A-04 · Knowledge

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34. The output of a two-input XOR gate is 1 when:

  1. The inputs are different
  2. Both inputs are 0
  3. At least one input is 1
  4. Both inputs are 1

Answer: A) The inputs are different

Explanation: XOR (exclusive OR) is 1 for inputs 01 and 10, and 0 when the inputs are equal. SLO CS-11-A-01 · Knowledge

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35. An attacker injects a malicious script into a web page that runs in other users' browsers. This is:

  1. Cross-site scripting (XSS)
  2. DDoS
  3. Phishing
  4. Brute-force attack

Answer: A) Cross-site scripting (XSS)

Explanation: XSS exploits websites that display user input without sanitising it. SLO CS-11-A-04 · Understanding

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36. UML (Unified Modeling Language) is mainly used during which SDLC phase?

  1. Testing
  2. Maintenance
  3. Design
  4. Deployment

Answer: C) Design

Explanation: UML diagrams (use case, class, sequence) describe the design of a system before coding. SLO CS-11-A-02 · Knowledge

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37. Which access method is used in a ring topology?

  1. CSMA/CD
  2. Token passing
  3. Broadcasting to a hub
  4. Polling by a server only

Answer: B) Token passing

Explanation: A token circulates around the ring; only the node holding the token may transmit. Ethernet/bus networks use CSMA/CD. SLO CS-11-A-03 · Knowledge

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38. Which test checks how a system behaves when the number of users grows towards its limit?

  1. White box testing
  2. Syntax checking
  3. Load testing
  4. Unit testing

Answer: C) Load testing

Explanation: Load/stress testing prepares a system for scale and reliability. SLO CS-11-A-03 · Understanding

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39. An error in a program that produces incorrect results is called a:

  1. Compiler
  2. Prototype
  3. Bug
  4. Patch

Answer: C) Bug

Explanation: A bug is a defect; finding and removing it is debugging. SLO CS-11-A-02 · Knowledge

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40. Simplify F = A + AB (absorption law).

  1. A + B
  2. B
  3. AB
  4. A

Answer: D) A

Explanation: A + AB = A(1 + B) = A 1 = A. SLO CS-11-A-01 · Application

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41. How many cells does a Karnaugh map for 3 variables have?

  1. 8
  2. 6
  3. 16
  4. 9

Answer: A) 8

Explanation: A K-map has one cell per minterm: 2^3 = 8 cells (a 2 × 4 grid). SLO CS-11-A-01 · Knowledge

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42. A DDoS attack tries to:

  1. Encrypt files and demand a ransom
  2. Steal passwords by watching keystrokes
  3. Guess passwords one by one
  4. Make a service unavailable by flooding it with traffic from many computers

Answer: D) Make a service unavailable by flooding it with traffic from many computers

Explanation: Distributed Denial of Service overwhelms a server with requests from many (often hijacked) machines. SLO CS-11-A-04 · Knowledge

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43. In encryption, the readable original message is called:

  1. Key
  2. Ciphertext
  3. Hash
  4. Plaintext

Answer: D) Plaintext

Explanation: Encryption turns plaintext into ciphertext; decryption reverses it. SLO CS-11-A-04 · Knowledge

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44. For F = A'B'C' + A'BC' + AB'C' + AB'C + ABC' + ABC, the K-map gives:

  1. A + B
  2. A'C
  3. A + C'
  4. AC'

Answer: C) A + C'

Explanation: Group the A = 1 row (A) and the four C = 0 cells including the wrap-around (C'): F = A + C'. SLO CS-11-A-01

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45. Ensuring every branch of an if–else statement executes at least once is part of:

  1. acceptance testing
  2. white-box testing
  3. black-box testing
  4. load testing

Answer: B) white-box testing

Explanation: White-box testing is based on the internal structure of the code. SLO CS-11-A-02

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46. Deciding what a logged-in user is allowed to access is:

  1. phishing
  2. authentication
  3. encryption
  4. authorization

Answer: D) authorization

Explanation: Authentication proves identity; authorization grants permissions. SLO CS-11-A-04

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47. An email pretending to be from your bank asking you to "verify your password" is:

  1. phishing
  2. a firewall
  3. a DDoS attack
  4. XSS

Answer: A) phishing

Explanation: Phishing tricks users into revealing sensitive information. SLO CS-11-A-04

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48. A car alarm sounds when the engine is ON and the seat belt is NOT fastened. Which gate combines the two conditions?

  1. OR
  2. NOR
  3. AND
  4. XNOR

Answer: C) AND

Explanation: Both conditions must be true at the same time, which is AND (with a NOT on the belt signal). SLO CS-11-A-01

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49. Self-replicating malware that spreads over networks without attaching to files is a:

  1. worm
  2. cookie
  3. trojan
  4. virus

Answer: A) worm

Explanation: Worms spread by themselves; viruses need a host file. SLO CS-11-A-04

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50. Which gate is called an "equality detector"?

  1. NAND
  2. XOR
  3. OR
  4. XNOR

Answer: D) XNOR

Explanation: XNOR outputs 1 when both inputs are equal. SLO CS-11-A-01

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