MCQs / Computer Science / Unit 1: Computer Systems

Unit 1: Computer Systems MCQs — Computer Science

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.

1. Which Boolean identity is correct?

  1. A overlineA = 1
  2. A + A = 2A
  3. A 1 = 1
  4. A + overlineA = 1

Answer: D) A + overlineA = 1

Explanation: Complement law: A + overlineA = 1 and A overlineA = 0. Also A + A = A and A 1 = A. SLO CS-11-A-01 · Knowledge

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2. 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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3. 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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4. A 3-variable K-map has 1s in all four cells where A = 1 (and 0s elsewhere). The simplified expression is:

  1. A
  2. ABC
  3. AoverlineB
  4. A + B + C

Answer: A) A

Explanation: A group of four adjacent cells removes two variables. Only A stays constant (= 1) across the group, so F = A. SLO CS-11-A-01 · Application

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5. In a Karnaugh map, cells next to each other differ in:

  1. Exactly two variables
  2. All variables
  3. No variables
  4. Exactly one variable

Answer: D) Exactly one variable

Explanation: K-map rows and columns follow Gray code (00, 01, 11, 10), so neighbouring cells differ in only one bit. That is what allows grouping. SLO CS-11-A-01 · Knowledge

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6. 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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7. 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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8. Which task is an example of black box testing?

  1. Testing each branch of an if-statement using the code
  2. Reading the source code to check every loop
  3. Measuring how a function runs internally
  4. Entering login details and checking whether the dashboard opens

Answer: D) Entering login details and checking whether the dashboard opens

Explanation: Black box testing checks inputs and outputs without looking at the code. White box testing uses knowledge of the internal code. SLO CS-11-A-02 · Understanding

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9. 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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10. Using a password and a code sent to your phone to log in is called:

  1. Firewall filtering
  2. Hashing
  3. Single sign-off
  4. Two-factor authentication (2FA)

Answer: D) Two-factor authentication (2FA)

Explanation: 2FA combines something you know with something you have. SLO CS-11-A-04 · Knowledge

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11. A hospital's proposed software will cost more than its budget and expected benefits. Which feasibility concern is this?

  1. Technical feasibility
  2. Economic feasibility
  3. Legal feasibility
  4. Operational feasibility

Answer: B) Economic feasibility

Explanation: Economic feasibility compares costs with benefits. SLO CS-11-A-02 · Understanding

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12. 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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13. How many cables are needed to connect 6 computers in a fully connected mesh topology?

  1. 6
  2. 12
  3. 30
  4. 15

Answer: D) 15

Explanation: Links = dfracn(n-1)2 = dfrac6 52 = 15. SLO CS-11-A-03 · Application

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14. Which statement best describes the difference between analog and digital signals?

  1. Digital signals vary continuously; analog signals have only two values
  2. Analog signals vary continuously; digital signals take only discrete values (e.g. 0 and 1)
  3. Both carry only binary values but at different voltages
  4. Analog signals are always faster than digital signals

Answer: B) Analog signals vary continuously; digital signals take only discrete values (e.g. 0 and 1)

Explanation: An analog signal can take any value in a range (like a sound wave). A digital signal has a limited set of levels — in computers just 0 and 1. SLO CS-11-A-01 · Knowledge

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15. 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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16. By the principle of duality, the dual of A + 0 = A is:

  1. A + 1 = 1
  2. overlineA + 0 = overlineA
  3. A 0 = 0
  4. A 1 = A

Answer: D) A 1 = A

Explanation: To form the dual, swap + with and 0 with 1 (variables stay unchanged): A + 0 = A ;to; A 1 = A. SLO CS-11-A-01 · Understanding

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17. Which topology offers the highest reliability because data has many alternative paths?

  1. Bus
  2. Star
  3. Mesh
  4. Ring

Answer: C) Mesh

Explanation: In a mesh, each node has several links, so one failure doesn't break communication. SLO CS-11-A-03 · Understanding

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18. What is the main disadvantage of a star topology?

  1. One broken cable stops the whole network
  2. If the central hub fails, the whole network stops
  3. Data travels in one direction only
  4. It needs the most cable of all topologies

Answer: B) If the central hub fails, the whole network stops

Explanation: The hub/switch is a single point of failure, though one broken cable affects only one computer. SLO CS-11-A-03 · Understanding

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19. Which of the following is used to prevent unauthorized access to a network?

  1. Spyware
  2. Firewall
  3. Worm
  4. Virus

Answer: B) Firewall

Explanation: A firewall filters incoming and outgoing traffic according to security rules. The others are malware. SLO CS-11-A-04 · Knowledge

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20. 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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21. Two switches are connected in series with a bulb. The bulb glows only when both switches are ON. This circuit behaves like which gate?

  1. NOT
  2. OR
  3. AND
  4. XOR

Answer: C) AND

Explanation: Series switches: current flows only if A and B are closed. Parallel switches behave like OR. SLO CS-11-A-01 · Understanding

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22. Using De Morgan's theorem, overlineA + B equals:

  1. overlineA + overlineB
  2. overlineA B
  3. A B
  4. overlineA overlineB

Answer: D) overlineA overlineB

Explanation: De Morgan: overlineA + B = overlineA,overlineB and overlineA B = overlineA + overlineB — “break the bar, change the sign”. SLO CS-11-A-01 · Application

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23. How many rows does the truth table of a Boolean expression with 3 inputs have?

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

Answer: C) 8

Explanation: Each input has 2 values, so 2^3 = 8 combinations. SLO CS-11-A-01 · Knowledge

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24. 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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25. 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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